Tag Archives: gravity

Degrees of Friction

In the last Project we found that rough surfaces cause more friction between objects. There are several degrees of friction to explore. Force is often measured in Newtons which is mass in kg times distance in m divided by time in seconds squared.

You might have noticed I am not doing a lot of math but knowing what the units are can be important when you do.

materials for project

Question: How does friction vary?

Materials:

Spring scale

Note: If you do not have a sensitive spring scale, you can use a thick rubber band. You will not be able to measure the friction but you can see what it does. Get a thick rubber band so the loop is about 5 cm long. Use a paperclip to make a hook on one end.

Wood block

Screw eye

Sandpaper

Smooth board

Procedure:

Put the screw eye in one end of the wood block

Attach the spring scale to the eye

Lift the block and get the measurement force in Newtons

block hanging from spring scale

Gravity is the force pulling the block down creating weight in grams or force in Newtons.

Place the block of wood on one end of the board

Watch the measurements on the scale as you very slowly pull on the block

Check the measurement on the scale as you pull the block down the board

starting and moving a block shows degrees of friction

There is friction even between the plain board and the plain block. It takes more force to start the block moving than to keep it moving across the board.

Repeat this two or three times observing what the scale does as you apply force on the block

Prop up the end of the board 10 cm and repeat your measurements

Move the prop to the other end of the board 10 cm and repeat your measurements

Remove the prop

pulling the sandpapered block up the ramp

Can you draw the force vectors for this? The hand is pulling upward. The sandpaper is pulling back. Gravity is pulling downward which splits for both down straight and down the ramp.

Tape sandpaper on the bottom of the block

Watch the measurements as you very slowly pull on the block then pull it down the board

Prop up the end of the board 10 cm and repeat your measurements

Move the prop to the other end of the board and repeat your measurements

Remove the prop

Tape sandpaper on the board

Watch the measurements as you very slowly pull on the block then pull it down the board

Prop up the end of the board 10 cm and repeat your measurements

Move the prop to the other end of the board and repeat your measurements

Note:

If you use the rubber band, watch how it stretches as you slowly pull on the block then pull the block along the board. Describe what the rubber band does.

Observations:

Force to lift the block

Greatest force before the block moves

pulling block down the ramp

Going down the ramp gravity helps pull the block down so less force is needed to move the block and keep it moving.

Plain block, plain board

No prop

Top prop

Bottom prop

Sandpaper block, plain board

No prop

Top prop

Bottom prop

Sandpaper block and board

No prop

Top prop

Bottom prop

Force to pull the block

Plain block, plain board

No prop

Top prop

Bottom prop

Sandpaper block, plain board No prop

Top prop

Bottom prop

Sandpaper block and board

No prop

Top prop

Bottom prop

Conclusions:

Did you need the same amount of force to start the block moving as you needed to keep it moving?

Why do you think this is the case?

Was the amount of force needed to pull the block the same as the force to lift the block?

Why do you think this is the case?

sandpaper on block and board going up ramp

Sandpaper on both the block and the board causes more friction between them so it takes more force to move the block. Going up the ramp, gravity pulls the block down so even more force is needed.

Did you use the same force to pull the block down the board, along the board and up the board?

Why do think this is the case?

Tires use friction to keep a car on the road and moving down the road. How does ice on the road change things?

Does a car engine work harder to make a car go up a hill or down a hill? why do you think so?

 

What I Found Out:

I forgot my screw eye. I took a long piece of tape and made a loop with it. This worked fine as the block had a small mass.

My wood block had a mass of 49 g on the spring scale. This was the same as .49 Newtons.

The smooth block didn’t move until the scale read .14 N. It was really hard to get a good reading as the scale went up then suddenly dropped as the block moved. It only took .09 N to pull the block across the board. There were two degrees of friction: one to start the block moving and one to keep it moving.

sandpapered block pulled across board

Sandpaper is rough. Putting sandpaper on the block means more force is needed to move the block.

When I propped up one end of the board 10 cm and placed the block at the top, the block almost moved by itself. Only .06 N started the block moving and the scale dropped to less than 0 N to keep it moving down the ramp.

Pulling the block up the ramp was much different. This took .22 N to start the block moving and .18 N to keep it moving.

Putting sandpaper on the block made it much harder to move the block. On the level it took .48 N to move and .4 N to keep moving. Going down the ramp was easier with only .3 N to move the block and .1 N to keep it moving. Going up the ramp took. 56 N to move the block and .3 N to keep it moving.

Having sandpaper on both the block and the board was even more difficult. Now it took .52 N to start the block moving on the flat board and .48 N to keep it moving. Sliding down the board took .32 N to start the block moving and .18 N to keep it moving. Going up the ramp took .7 N to start the block moving and .36 N to keep it moving.

pulling block up ramp

Pulling the plain block up the board takes more force than when the board was flat or the block was going down the ramp. It takes more force to start the block moving than to keep it moving. Different forces cause different degrees of friction.

Every time it took more force to start the block moving than it did to keep it moving. It was as though the block and board resisted the motion as long as possible then suddenly couldn’t hold still any longer. The block shot forward, jerked and then moved steadily.

I think friction held the block in place. Once enough force was applied, this friction was overcome. Then less friction was working on the block as it moved. The block also had momentum because it was moving and that helped overcome the friction.

When I held the block up, gravity pulled it down .49 N. Gravity always pulls down. When the block is resting on the flat board, gravity keeps it on the board so only the force to overcome gravity is needed to move the block. The sandpaper added enough friction so the force needed was as much as gravity or more with both pieces covered with sandpaper.

When the block was going down the ramp, gravity helped pull the block down. this is why it took less force to pull the block down a ramp than on a flat surface. Pulling the block up the ramp added gravity to the friction so more force was needed.

Ice is very smooth and slippery. Road pavement is rough. There is less friction on a smooth surface like ice so a car can slide instead of staying on the road.

It takes more force to go up a hill than down a hill because gravity pulls the car down the hill. The engine will work harder to go up the hill.

Friction changes for many reasons. It is a force that resists movement of an object. This project show many degrees of friction. Take a look for where these show up.

Physics 15 Projectile Motion

There’s straight line motion. Our balls and cars have shown us a little about it.

There’s pendulum motion. Nuts on strings showed us about this.

There’s circular motion. We used a nut on a string to find out a little about it.

There’s harmonic motion. A Slinky and springs showed us a little about this.

One last type of motion is projectile motion.

What happens if you throw a ball straight up?

If you don’t dodge, it will come straight down and hit you. Why?

If you throw a ball across a room, it curves down to the floor. Why?

 

Question: How does projectile motion work?

Materials:

Ball

Stopwatch

Paper

Pencil

Procedure:

Toss the ball up from your hand

tossing a ball diagram

The ball leaves the hand, goes up then comes back down into the hand.

Observe how the ball goes up and down

Catch it when it returns to your hand

If you have a friend to help, have your friend gently toss the ball across a space

Observe how the ball moves

thrown ball diagram

Throwing a ball or other projectile gives it an arch shaped path.

Play catch outside with your friend

Start with gentle tosses and gradually throw the ball harder

Observe how the motion of the ball changes as you throw it harder

Get your stopwatch ready. Stand ready to throw your ball straight up.

Start the stopwatch and throw your ball straight up as hard as you can [It helps to have a friend help with this.]

Stop the stopwatch when the ball hits the ground

Repeat this only if you did not get the stopwatch stopped on time

Observations:

Draw your ball going up and down one time

Describe how your ball goes up and down

Draw your ball going across a space

Describe the motion of your ball

Describe how the motion of your ball changes as the throws get harder

Time for your ball to go up and down:

Conclusions:

What makes your ball go up?

Newton’s First Law of Motion says an object in motion will continue that motion unless acted on by another force. What force keeps your ball from going up forever?

Why do you think the projectile motion of your ball changes as you change how you throw it?

vectors for a thrown ball

Throwing a ball is more like the projectile motion people think of because the ball goes over a distance. At the beginning most of the force pushes the ball up, some goes sideways and gravity pulls down. At the top of the arch there is no more force pushing the ball up but it still has force pushing it sideways and gravity pulls it down. When the ball lands, only gravity is still pulling on the ball.

Draw your ball going across a space. Show your ball at the beginning, middle and end of the toss.

Add vectors to show how the forces are acting on your ball at each point to change how it moves.

How does projectile motion work?

Why can’t you use an average time for throwing your ball straight up?

Analysis:

How high did you throw your ball?

Your ball spent half its time going up and half its time coming down. Divide your time in half.

What provided the force to make the ball go up?

vectors for tossing a ball

When the ball first leaves the hand, most of the force is pushing the ball upward with gravity pulling against it. At the top of the loop, gravity and upward force cancel each other out and the ball stops. Then gravity pulls harder than the upward force so the ball falls back down into your hand. This is projectile motion.

What provided the force to make the ball come down?

Remember the formula from the last Project was a = d/t2

This time we know the acceleration is 9.8 m/s2 and the time and want to know the distance. We can rearrange the formula to be d = at2

Calculate how high you threw the ball.

 

What I Found Out

First I found out this Project is much easier with two people and I am only one so pictures were not possible. So I did drawings on my computer.

Tossing a ball up and down in one hand isn’t hard. The ball went up out of my hand then stopped and fell back down into my hand.

Playing catch can be fun. When the ball is tossed easily, it arches up then down into the other person’s hands. As the ball is tossed harder, the arch flattens out until it is almost a straight line.

Throwing or tossing a ball uses force from my hand. Gravity is always pulling down on the ball.

diagram of a ball thrown hard

Throwing a ball harder means it is going faster so gravity doesn’t slow it down as fast flattening the curve the ball makes.

The ball must go fast enough to overcome gravity. The harder I throw the ball, the faster it goes and the longer before gravity slows it down enough to make it fall.

In projectile motion the ball starts off with lots of force pushing it upwards. Gravity pulls a little of that force at a time slowing the ball down. At the top of the arch gravity is equal to the force making the ball go forward. Then gravity is greater making the ball fall down.

When a ball goes straight up, gravity pulls down until the ball stops and starts to fall down. Even if I try very hard, I won’t throw the ball with the same force every time so I must time each throw separately.

When I tossed my ball up, it took 1.94 sec to hit the ground. Half the time is .97 sec. Squaring the time gives .88 s2. Multiplying that by 9.8 m/s2 tells me I threw the ball 8.6 m or about 28 feet up.

Physics 14 Gravitational Acceleration

As we’ve seen and used, gravity pulls things down to the ground. It causes what physicists call uniform acceleration. This means the object accelerates the same amount each second or unit of time.

Another way of saying this is that the object going speed in meters/second [m/s] per second moving [1/s] or acceleration [a] is m/s2.

In another Project we found gravitational acceleration is the same for large or small masses. Air can slow the object down due to friction. Remember the paper airplanes and the fan?

In this Project we will try to measure gravitational acceleration in two ways. This will require doing some math. Both ways require the stopwatch start when the ball is released so the ball starts from rest or velocity equal to zero.

materials for the project: ramp, ball, meter stick, stopwatch

Question: What is the value of gravitational acceleration?

Materials:

Ramp

Ball

Meter stick

Stopwatch

Procedure:

This is the hardest way. You drop the ball while timing how long it falls. The farther it falls, the easier it is to start and stop the stopwatch as the ball hits the ground. You must know exactly how far in meters the ball falls.

holding ball ready to drop it

The ball must be held at the tape mark each time before it is dropped.

Mark the height you will drop the ball from.

Measure the distance from the floor to the mark in meters

Stand with the ball in one hand and the stopwatch in the other hand or have a friend help

Start the stopwatch at the same time you drop the ball

Stop the stopwatch when the ball hits the floor

Do this at least three times

ramp on chair

The ramp was taped to the chair.

If you remember other Projects, running the ball down the ramp makes it take longer to get to the ground. This makes timing the ball easier. You must know exactly how far the ball rolls down the ramp to the ground.

Set up your ramp

I used a ramp two meters long propped and taped to a chair.

Mark your starting line on the ramp

Measure the distance from your mark to the floor in meters

Hold the ball in one hand at the starting line and the stopwatch in your other hand or have a friend help

Let the ball go at the same time you start the stopwatch

Stop the stopwatch when the ball reaches the floor

Do this at least three times

Observations:

Time for the ball to fall:

1st:

2nd:

3rd:

Time for the ball to go down the ramp

1st:

2nd:

3rd:

Analysis:

Find the average time for the ball to fall

Find the average time for the ball to go down the ramp

[Remember you add up all the times then divide by the number of times to find the average.]

To calculate the gravitational acceleration we will use the formula: a = v/t = d/t/t

The a is acceleration.

The v is the velocity of the ball when it hits the floor. You don’t know the velocity but velocity is distance divided by time and you do know these.

The d is the distance the ball travels in meters.

The t is the time in seconds.

Calculate the acceleration by dividing the distance in meters by the time in seconds then the quotient by the time in seconds again to get the acceleration for one second.

ball speeding down ramp

The ramp was steep so the ball sped down it quickly making timing difficult.

Use the same formula and the distance down the ramp and time for the ramp to calculate the acceleration down the ramp.

Conclusions:

Why is measuring the distance so important?

Why is measuring the time accurately so important?

Why do you use an average time?

Would it be better to have more times to use to get your average time? Why do you think so?

Why should the acceleration you calculate for the two methods of timing be about the same?

Were your two times the same? Why do you think this was the case?

The gravitational acceleration is thought to be 9.8 m/s2. Were your calculated accelerations close to this? Why do you think this was the case?

 

What I Found Out

This project seems so easy to do. I measured my ramp carefully so it was 2 m long. It was set up with a steep slope.

When I tried to time the ball going down the ramp, I had problems. It was easy to start the ball and the stopwatch at the same time. It wasn’t so easy to stop the stopwatch when the ball got to the floor.

Dropping the ball was even harder. Again it was easy to start the ball and the stopwatch at the same time. I’m positive the ball bounced before I got the stopwatch stopped.

This is definitely a project requiring two people to do it well.

The formula required two measurements. One was the distance the ball went. Since this distance is divided by the square of the time, a little mistake in measuring the distance can make a big difference in the answer.

The time is squared or multiplied by itself. Any mistake in the time becomes very big.

I measured the time four times each way the ball went. The times were very similar for going down the ramp with a span of only .03 sec between the lowest and highest times.

The times for dropping the ball had a range of .1 sec between the lowest and highest time. The range of the squares would be .19 sec2 to .29 sec2. That much difference would make a big change in the acceleration I calculated.

dropping the ball

My ball dropped 1.5 m faster than I could start and stop the stopwatch. This made getting good times difficult.

Using an average time smoothed out these extremes to give me a better time for my calculations.

The procedure said to use three time measurements. I chose to use four because my measurements were so different. If the three measurements had been more similar, I would have used only three.

I think the number of measurements you use depends on how similar they are.

When I calculated my accelerations I got 1.5 m/s2 for dropping the ball and 1.3 m/s2 for the ramp. Since the pull of gravity was the same for both methods, the acceleration should be about the same.

My calculated acceleration was very different from the accepted gravitational acceleration of 9.8 m/s2, not even close. I am not sure why my values were so different.

One possibility is the time. It was very hard for me to get a good time even though my values were similar.

What I would like to do is repeat this project with someone to help me. I would make two other changes.

First I would lower the angle of the ramp so the ball would go down a little slower making timing it easier.

Second I would lengthen the distance to at least two meters dropping the ball. This would give a little more time to stop the stopwatch before the ball bounced.

Physics 9 Acceleration

Speed is the distance something goes in a certain amount of time. The speed stays the same. Except we know things go faster or slower and change direction. This is acceleration.
When Albert Einstein developed his Theory of Relativity, he made an assumption about gravity. He said it was a form of acceleration.
If gravity is a form of acceleration, it will make an object’s speed change over time.
Galileo worked with gravity too. He rolled balls down a ramp and found out something interesting about their final speeds.

setting up the acceleration project

I used the same set up I used for measuring speed. the ball ramp was taped to the chair with the meter stick on the floor.

Question: How does gravity change a ball’s speed?
Materials:
Ball ramp
Ball
Meter stick
Stop watch
Procedure:
Mark a place on the ramp to start rolling the ball
Measure the distance the ball will roll and divide it by four
Measure one fourth the distance and put a mark

marks on ball ramp

Each place on the ramp must be clearly marked. Will the ball go twice as fast from the top mark as from the half way mark?

Measure one half the distance and put a mark
Measure three fourths the distance and put a mark
Set up your ramp with the top mark0.5 m high
Set up the meter stick on the floor beside where the ball will roll with the beginning 10 cm from the end of the ramp
Write down how you think the ball’s speeds will compare for the four different starting points [Will the ball go half as fast when started half way down the ramp?]
Do at least three trials starting the ball from each mark.
You will start the stop watch when the ball reaches the beginning of the meter stick and stop it when the ball is at the end of the meter stick.
Observations:
Write down the four distances on the ramp:
Highest 1:
2:
3:
4:
How will the speed of the ball compare for each starting point?
Times for 1:
1:
2:
3:
Average
Times for 2:
1:
2:
3:
Average:
Times for 3:
1:
2:
3:
Average
Times for 4:
1:
2:
3:
Average

releasing ball on ramp

Aiya Taylor helped me with this project by letting go of the balls on the ramp. Help is important for these projects.

Analysis:
Calculate the average time for each starting point by adding up the times for the trials and dividing by the number of trials.
Draw a graph of speed and height. (Use 1/4, 1/2, 3/4 and 1 for the height.)
Conclusions:
Are you measuring final speed or acceleration? Why do you think so?
Is this measurement a good way to judge acceleration? Why do you think so?
Speed is constant so the line on your graph would be straight. Is your line straight?
Galileo decided gravity added acceleration at meters per second (speed) per second. This gives a curved line on a graph. Is your line curved?
Does your graph show speed or acceleration?

What I Found Out:
My ball had an average time of 44 seconds for the top mark. The time decreased to 39 seconds for the 3/4 mark. The time increased to 47 seconds for the 1/2 mark. The 1/4 mark had a time of 93 seconds.
It was hard to get good times for each trial run. But the time was definitely increasing as the height decreased. I think the 3/4 mark average was not accurate.
Because the ball was running on the level floor when I measured the time, I was measuring final speed not acceleration. The final speed was produced by the acceleration on the ramp so it was a good way to compare how much acceleration the ball gained at each height.
My graph was not a straight line so it showed acceleration.

Physics 5 Gravity and Galileo

Even though Sir Isaac Newton is famous for his Laws of Motion, Galileo studied how gravity affected motion long before Newton did. He didn’t have a good clock or watch with a second hand or any idea about a stopwatch. He used his pulse or a water clock that has a bowl of water with a tiny hole so the water drips out at a steady rate.

Galileo did the best he could with the equipment he had and did write down laws of motion very similar to those later written down by Newton. He was the first scientist to test some ideas people had believed for years and never thought to test.

Like Galileo we will be using the force of gravity for several Projects. We have used it for the Projects we’ve already done. So we will take a closer look at gravity and some ways it works and things that affect it.

This Project works much better with two people doing it.

balls and ramp needed for this Project

Question: What are two things Galileo discovered about gravity?

Materials:

2 balls alike in substance, size and weight

2 balls alike in size [Use solid balls] but different in weight [at least double]

Grooved ramp at least a meter long

Procedure:

Look over the two balls alike in size but different in weight

Mass the two balls

You will drop the two balls from the same height at the same time

Predict which option will be true and why you think so:

1) The heavy ball will fall faster

2) Both balls will fall at the same speed

3) The lighter ball will fall faster

One person drop the balls from the same height at the same time while the other person watches to see which option is true.

dropping the balls

Dropping two balls at the same time is harder than it sounds. Using one hand to hold and release both balls worked the best for me.

Try dropping the balls from different heights

Like Galileo we will be timing how fast a ball or car moves when pulled by gravity

Look over the two balls alike in size, substance and weight

When you use a stopwatch, you click it on when the ball or car begins to move and click it off when a certain distance is covered.

Drop one of the balls from a meter high

Could you click a stopwatch on and off in that time?

Set up the grooved ramp so one end is one meter high

ready to release balls

I got a large piece of cardboard and folded it double to make a stiff ramp. It had to be taped to keep the folded parts together.

One ball will run down the ramp while the other drops the same height to the floor

Predict which option will be true and why you think so:

1) The ball dropping straight to the floor will drop fastest

2) Both balls will fall to the floor at the same time

3) The ball going down the ramp will get to the floor first

One person holds a ball at the end of the ramp and one over the floor at the same height

That person lets the balls go at the same time while the other person watches to see which option is true

Observations:

Describe the two balls:

Mass of Ball 1:

Mass of Ball 2:

Write down your prediction and reason for choosing it

Describe what happens when the two balls are dropped:

falling balls

A heavy and a light ball fall together. Gravity pulls on both the same.

Explain why you can or can’t use a stopwatch to time how fast the ball drops:

Describe the two balls:

Write down your prediction and reason for choosing it

Describe what happens when one ball drops straight down and the other goes down a ramp:

Conclusions:

What forces are acting on the two balls as they fall when you drop them?

Which force is the most important? Why do you think this?

Does mass seem to matter to this force? Why do you think so?

What forces are acting on the two balls, one dropped and one on the ramp?

Ball dropping and ramp

The ball going straight down got to the floor long before the ball rolling down the cardboard ramp even though gravity was the force pulling on both.

Which force seems to matter the most? Why do you think so?

Does distance traveled seem to matter to this force? Why do you think so?

What do you think would happen if the ramp were more level? Try it and find out.

Why do you think this is the case?

What do you think would happen if the ramp were steeper? Try it and find out.

Why do you think this is the case?

Do you think it is possible to use a stopwatch to time a ball going down a ramp? Why do you think this?

 

What I Found Out

I had to use a ping pong type of ball for my light ball and a rubber ball for the heavy one. It seems easy to think the heavier ball will fall faster because it is heavier. I can’t really predict this because I know what will happen.

When the balls dropped, both dropped straight to the floor. They hit the floor at almost the same time. I found I had to have both balls in one hand to be sure they dropped at the same time.

Gravity was pulling the balls down. Air was pushing up on the balls like it did the sheet of paper but the balls were too small and heavy for the air to push hard enough to slow them down.

Gravity doesn’t seem to care about mass as the balls hit the ground at the same time. It pulls the balls down very fast, faster than I could start and stop a stopwatch.

When I set up my ramp, I thought the two balls would hit the floor at the same time even though one ball had to travel much farther. Gravity was pulling the same on both so they should fall at the same speed.

Thinking it over now I can see the ball going down the ramp would have to get to the floor after the ball dropped straight to the ground. This is what happened. Changing the slope of the ramp made the ball take more time on lesser slopes and shorter times on steeper ramps.

Gravity does pull the same on the two balls but the distance does matter. Since a ball travels down a ramp more slowly than being dropped, I think I could time it with a stop watch.

 

Physics 4 Vectors

Forces hold things in place and make them move. Some of the forces we can see. Others we know are there but can’t see. We need a way to show all of these forces. That is what vectors do.

Question: How do vectors show forces?

Materials:

Paper

Pencil

Ruler

Procedure:

Open your Journal and write Project 4

Remember Project 1 where the block sits on the table

Draw a table with legs sitting on the floor

drawing of table

Your drawing doesn’t need to be fancy. A simple set of boxes will work like this will work fine.

Draw the block sitting on the table

Gravity pulls down on the block so draw an arrow pointing down from the block

gravity arrow in block

Gravity pulls down on the block so it sits on the table. The vector arrow points down.

Note: Gravity always points toward the center of the Earth which is usually down

If only gravity was pulling on the block, it would fall to the ground so some force is pushing back on the block. The table is pushing back so draw another arrow next to the other arrow but pointing up.

table vector arrow is added

The table pushes back against the block just as hard as gravity pulls it down so a vector arrow the same size pointing up is added to the block.

How long should this arrow be? Vectors show speed and direction. We are not measuring speed but only showing direction in this Project.

Gravity pulls down. If the arrow pointing up is longer showing greater force, there would be more force pointing up than down. The block would float up off the table. It didn’t so the arrow isn’t longer than the gravity arrow.

If the arrow is shorter than the gravity arrow, the force of gravity would be greater than that of the table. The block would pull through the table and fall to the floor. It didn’t so the arrow isn’t shorter.

The arrows must be the same length as the forces are equal and opposite to each other.

gravity vector arrows put in table legs

Since the table is not floating away, gravity is pulling down on the legs so a vector arrow pointing down is put in each leg.

Since the table isn’t floating away, gravity must be pulling down on it too. Draw vector arrows for gravity to hold each table leg on the floor.

floor vector arrows added

The floor pushes up against the table legs just as hard as gravity pulls down on the legs so the arrows are the same length as those vectors but pointing up.

Since the table isn’t sinking into the floor, the floor is pushing back against the table legs. Draw those vector arrows.

push vector arrow added

A vector arrow showing the push on the block is added aimed at the block which was the direction of the force.

Next remember what happened when you pushed on the block. Your finger was a force acting on the block. Draw a vector arrow for that force.

Did the block move? Which way did it move? Since the block moved, there was no force pushing back against your finger so there will be no arrow.

all vector arrows drawn

Every pair of force vectors have the arrows equal and opposite except for the last pair. The pushing force arrow must be longer than the block resistance force arrow for the block to move.

Now wait a minute! When I pushed against my block of wood, the end of my finger flattened so the block did push back. But the block moved so the force the block pushed against my finger was much less than the push my finger gave the block. I will draw a little arrow from the block toward my finger.

paper airplane

Paper airplanes are fun to fly. They fly and fall because of forces pushing and pulling on them. Those forces can be drawn as vectors.

Now let’s draw vectors for a paper airplane:

Draw the airplane flying

What force made the airplane fly?

You threw it so you exerted a force on it. Draw that arrow pushing the back of the airplane.

thrust vector on airplane

Throwing a paper airplane pushes it forward so the vector arrow pushes against the tail end.

Is gravity acting on the airplane? Gravity acts on everything on Earth so draw an arrow pointing down for gravity.

air vector on airplane

Like the sheet of paper, air pushes up on the wings of the paper airplane so the vector arrow points up toward the wing.

What is pushing up on the wings to keep the airplane up? Air pushes up.

Does the air keep the airplane up all the time? It didn’t keep mine up. So there is an arrow for the air pushing the wings up but it is less than the gravity.

gravity vector arrow on airplane

The paper airplane doesn’t fly forever so gravity pulls down on it which the vector arrow shows.

Where would the arrow for the fan pushing the airplane go? Draw it in.

Notice that this arrow is with the one from you throwing the airplane so the two add up.

air pushing airplane forward

When the air from the fan pushes the paper airplane, the vector arrow pushes against the airplane’s tail adding to the thrust vector from you throwing it.

Where would the arrow go for when the fan pushed against the airplane? For my airplane it would be the same length as the one for throwing the airplane because I did see it stop my airplane once.

air vector against airplane

When the air from the fan blows against the paper airplane, the vector arrow must point toward the airplane.

This last set of drawings shows one way vectors help a physicist understand the forces acting on an object. When forces act together, they add up. When forces act against each other, they cancel each other out.

 

Another way vectors show how forces work is shown with the car going down the ramp.

Draw the ramp with a car on it.

The car is racing down the ramp so the vector arrow goes down the ramp. Or does it?

car on ramp

The car is moving down the ramp so the vector arrow points down the ramp but is this correct?

Gravity is pulling the car down but gravity pulls straight down. So there should be an arrow pointing down from the car.

gravity arrow on car

Gravity pulls down on the car so a vector arrow points down from the car.

But the car moved down the ramp. So there is another arrow from the tip of the gravity arrow to the ramp spot where the car will be after a certain amount of time.

all force vector arrows on car

The gravity arrow and the forward arrow meet at the vector arrow on the ramp’s point as the two add up to that vector.

In this case vectors show the movement of the car is made up of two different vectors, one pulling down and one pulling across.

 

About Vectors

Vectors usually show both direction and acceleration. They are a way to see how forces add and subtract from each other so you can tell where an object will go when several forces push or pull on it at the same time.

For now the accelerating force we will work with will be gravity. The next Project will look at some ways gravity pulls objects down.

Physics 3 First Law of Motion

Perhaps you have noticed especially in Project 1 that something sitting on a table or anywhere does not move unless some force makes it move. That can be a contact force like a push or a pull. It can be a non contact force like gravity, magnetism or electricity.

A man named Sir Isaac Newton wrote this down as his First law of Motion:

An object at rest remains at rest as long as no net force acts on it. An object moving with constant velocity continues to move with the same speed and in the same direction as long as no net force acts on it.

materials to do the Project

Question: How does Newton’s First Law of Motion work?

Materials:

Small car

Meter long smooth board 15 cm wide or car track

Wood block 1 cm x 1 cm x 15 cm (The height should be the height of the car hood.)

Tape

Several thick books

Ruler

Penny and nickel

Procedure:

Open your journal and write the name of the project. Copy the table.

Journal page

Keeping a Journal of all of the Projects makes it easy to look up previous Projects.

Tape the small wood block across one end of the long board

block on board

The block is attached at the end of the board. Why is the block only as high as the car hood? Would a higher block change your results?

Draw a line across the other end of the board 1 1/2 times the length of the car from the end

starting line on board

The starting line is drawn across the board. Why is drawing the line important? Would starting the car at a slightly different place each time change the results?

Put books under the other end of the long board so the line is 10 cm off the floor [I put the line across the edge of the book so it was always in the same place.]

car on 10 cm high ramp

The car rolled down the ramp at 10 cm high then bounced off the block to a stop.

Set your car at the line and let it run down the ramp several times (If your car does not go straight down the ramp, get another car that does go straight down the ramp.)

Balance a penny on the roof of your car, set it at the line and let it go down the ramp

Measure from the block to where the penny lands and record it in the table

measuring to the penny from the 10 cm high ramp

The penny flew around 12 cm from the car on the 10 cm high ramp.

(If the coin rolls off, don’t count that trial run but do another until the coin lands flat.)

Repeat this with the penny two more times

Repeat this with the nickel three times

Raise the line to 15 cm off the floor

Repeat with the penny three times

Repeat with the nickel three times

Raise the line to 20 cm off the floor

Repeat with the penny three times

Repeat with the nickel three times

Observations:

Describe what happens when the car alone goes down the ramp

table 1

10 cm

Describe what happens when the penny is on the car when it goes down the ramp

Describe what happens when the nickel is on the car when it goes down the ramp

15 cm

Describe what happens when the penny is on the car when it goes down the ramp

car on 15 cm high ramp

The car went faster down the ramp, hit the block at the end and bounced back then went to the block and stopped.

Describe what happens when the nickel is on the car when it goes down the ramp

20 cm

Describe what happens when the penny is on the car when it goes down the ramp

Describe what happens when the nickel is on the car when it goes down the ramp

Analysis:

An average is found by adding the different values (the 3 distances) then dividing by the number of values (3)

Find the average distance the penny goes for each board height

measuring to the penny for the 15 cm high ramp

The distance to the penny doubled when the ramp was raised up to 15 cm.

Record the averages in the table

Find the average distance the nickel goes for each board height

Record the averages in the table

Draw a line graph of average distance against board height for the penny and nickel

Conclusions:

What force makes the car roll down the ramp?

car on 20 cm high ramp

The little car really roared down the ramp when it was raised to 20 cm high. It hit the block hard bouncing off the ramp and onto the table.

What force stops the car?

Why don’t the penny and nickel stop with the car?

measuring the penny distance for 20 cm

The penny went over 30 cm all three times when the ramp was raised to 20 cm. It rolled across the table several times too so I had to redo the runs.

Why do the penny and nickel travel differently for the same distance?

Why don’t the penny and nickel travel the same distance all three times?

What stops the penny and nickel?

What do you think would happen if you raised the ramp another 5 cm? Try it and find out.

How does Newton’s First law of Motion apply to your results?

 

What I found Out

Each time I raised the ramp, the car went faster. The coins went farther for each higher ramp. Gravity pulled the car down the ramp.

When the car went down the first ramp by itself, it rolled faster as it went down. When it hit the block on the end, it bounced back and rolled off the ramp.

The penny sat on the car hood. When the car hit the block, the penny flew out onto the table. The nickel went a few centimeters farther than the penny did.

When the ramp was raised to 15 cm, the car went faster and hit the block harder, bouncing back more. Once it bounced all the way off the ramp. The penny and the nickel went farther too. The nickel still went farter than the penny.

The car went even faster when the ramp was raised to 20 cm. The penny and nickel went farther than my ruler could measure so I had to move the ruler and add the extra.

The block stops the car with a push against it. The penny and nickel are above the block so no force acts on them and they keep going.

The nickel is heavier than the penny so it goes farther than the penny. Even though I tried to start the car at the same place each time, it wasn’t exactly the same so the car ran down the ramp a little differently so the coin flew off differently.

The penny and nickel fall to the table top. Gravity makes things fall so gravity must be what stops the coins from going any further.

I couldn’t raise the ramp higher this time. My car was very flat and the coins slid off the hood. I did use a higher ramp once before. The penny and nickel went into the table top in a short distance because the car was pointed down into the table top.

Newton’s First Law of Motion says an object at rest stays at rest and an object in motion stays in motion at the same speed and direction unless acted on by another force. The car and coin were pulled down by gravity. Gravity made them go faster the longer they went down the ramp.

At the end of the ramp the force of the block stopped the car. No force acted on the coins so they kept going until gravity pulled them down to the table.

 

 

Physics 1 What Is a Force

Be sure to start a Physics Journal to keep track of all your physics projects. Sometimes one Project will ask you to take another look at a Project you did earlier. A Journal makes this easy to do.

Physics journal

A physics journal doesn’t have to be fancy, just full of paper to write on. That way all or your observations are in one place, easy to find.

Physics can be very hard with lots of difficult math. But some parts of physics are much easier. Those are the ones we will be doing this year.

Physics tries to explain forces. What is a force? The easiest definition of a force is: A force is a push or a pull.

Since physics is about forces, we will start with some simple forces and how they work.

Physics Project 1 materials

Question: What is a force?

Materials:

2 Small blocks of wood

Ball

Scale

Procedure:

Open your Physics Journal and write the Project number

Physics Journal entry

In my Physics Journal I put only the Project number and question. then I list the observations, analysis and conclusions. If I did not have the materials and procedure on the computer, i would put those in my Journal too.

Set a block of wood on a table then leave the room

wood block on table

Left setting on a table a wood block sits there not moving.

Come back in the room and look at the block of wood

Did the block of wood move?

Push on the block of wood with a finger

Does the block of wood move?

pushing the block

Pushing on the wood block caused the block to move in the direction of the push.

Pull the block of wood using a finger

Does the block of wood move?

Hold the ball in your hand

Does the ball stay in your hand?

Drop the ball

What does the ball do?

Place one block of wood on the scale

Weighing Block 2

Block 2 has a weight of 57.57 g. It wavered between 57.56 g and 57.57 g but finally settled on 57.56 g.

Place the second block of wood on the scale

Put both blocks of wood on the scale

 

Observations:

Did the block of wood move?

What happens when you push the block of wood?

What happens when you pull the block of wood?

What does the ball do in your hand?

What does the ball do when you drop it?

How much does one block of wood weigh?

Weighing Block 1

Block 1 had a weight of 32.13 g.

How much does the second block of wood weigh?

How much do both blocks of wood weigh?

 

Analysis:

Add up the masses of the two blocks of wood

weighing both blocks

Together the wood blocks have a weight of 89.69 g.

Conclusions:

What makes the block of wood move?

Why doesn’t the block of wood float off the table?

Why does the ball sit in your hand?

ball in hand

A ball sits in the hand as long as it is held there.

Why does the ball drop when you let it go?

A contact force is a force you apply directly to an object. A non-contact force is a force applied to an object without touching it. Which of the forces applied to the block of wood and the ball were contact forces and which were non-contact forces? Explain why you think this.

Compare the masses of the two blocks on the scale and the two masses you added up. Do masses combine? Why do you think so.

Weight is a measurement of the pull of gravity. Do you think forces combine? Why do you think so?

 

What I Found Out

My block of wood didn’t move by itself. It did move when I pushed or pulled it. Pushing or pulling the block makes it move. It sits on the table because of gravity.

pulling the block

Pulling on the wood block caused the block to move across the table in the direction it was pulled in.

The ball sat in my hand because I was holding it until I dropped it. Then it fell down to the table. Gravity pulled the ball to the table.

dropped ball

This was not a bouncy ball. It fell to the table with a thud when I let go of it.

Pushing and pulling the block of wood were contact forces because I had to touch the block to make it move. Gravity is a non-contact force because it works without touching the block or the ball.

The total mass of the two blocks was 89.69g and the added mass of the two blocks was 89.69g which is the same so I think masses can be combined or added together. Gravity creates weight and is a force so I think forces can be combined.