# Physics 6 Meet the Inclined Plane

You are going to visit a friend and run up to the porch. How are you going to get onto the porch? You can jump up or you can walk up the steps.

Jumping up may be more fun. Walking up takes less effort. Those stairs are one kind of inclined plane.

Hailyann Workman’s help was greatly appreciated on this project. She seemed to think this was fun to do.

Question: How does an inclined plane work?

Materials:

3 Boards or pieces of stiff cardboard 10 cm wide and 0.5 m, 1 m and 1.5 m long

3 Bricks or 3 books about 5 cm thick

Spring scales

Meter stick

Block with loop

Procedure:

Set up the pile of books

Measure the height of the pile of books

Stand the block next to the pile of books

Use a spring scale to lift the block onto the books recording the force in grams

Remove the block

Measure the length of the boards

A short ramp is steep. Since work is force times distance, the longer distance makes the amount of work much higher.

Lean the short board on the pile of books to form an inclined plane or ramp

Set the block just on the edge of the board

Use the spring scale to pull the block up onto the books recording the force needed

Repeat this for each of the other boards

Observations:

Height of book pile:

Length of short board:

Length of medium board:

Length of long board:

Force needed:

To lift the block

Short board

Medium board

Long board

Analysis:

Calculate the work needed to get the blocks onto the books by multiplying the force on the scale times the height of the books. This is W = Fd or Work = Force times distance.

Using a simple machine is supposed to reduce the force needed to get the same amount of work done. Now that we know how much total work is needed, we can calculate the force needed for each of the inclined planes by rearranging the formula so W/d = F or work divided by distance equals force.

Calculate the force needed for each inclined plane.

Go back to the Procedure to complete the Project

Conclusions:

Compare the force you measured for each inclined plane with the force you calculated.

Compare the force needed for each ramp with the force needed for the others and to the force needed to lift the blocks.

A longer ramp has less of a slope making it easier to pull the blocks up.

What happens to the distance you must pull the block to use less force?

Would it be better to lift or use a ramp for a lightweight object? Why do you think so?

Would it be better to lift or use a ramp for a heavyweight object? Why do you think so?

What is the advantage of using a ramp?

What I Found Out:

This week I found Hailyann Workman to help me do this project. She is five and in kindergarten. She thought pulling the blocks up a ramp fun to do.

My stack of books was 15 cm tall. The scale registered 200 g lifting the blocks up. The work done was 3000 g-cm.

The short ramp was 44.5 cm long. The scale showed 150 g needed to pull the blocks up the ramp. I calculated 67.4 g-cm.

Next the blocks went up a 74 cm ramp using 100 g of force. I calculated needing 40.5 g-cm.

Remember finding out about friction last week? My long ramp was rough making lots of friction. Covering the ramp with paper made it smooth.

The long ramp was 109 cm and rough. It was hard to pull the blocks up so I taped paper onto the ramp to make it smooth. The blocks pulled up easily with 70 g of force needed. My calculated amount was 27.5 g-cm.

My measured forces were much higher than my calculated forces. Perhaps I misread the scale. My block was smooth but not slick. My ramps were not slick so there was friction.

The needed force did decrease as the ramp got longer. The medium ramp took half the force of lifting the blocks.

The distance increases as the force needed decreases.

A lightweight object can be lifted up to move it the shortest distance. A heavyweight object should be moved up a ramp. This takes more distance but requires less force and is easier on you than lifting something heavy.

A ramp is a way to decrease the force needed to move an object even though it increases the distance needed to move it.

# Physics 4 Exploring Work in Physics

Picture yourself helping to push a car. You shove. You turn around and push with your back. The car doesn’t move. Did you do any work?

According to your muscles you did a lot. According to the physics definition you did none.

In physics work is defined as moving something over a distance. Since the car did not move, you did no work. In physics this is written as: W = FD or work equals force times distance.

Question: How much work do you do?

Materials:

Spring scales [My set of 3 has a sensitive scale, a medium scale and a harder scale.]

Several blocks of different masses

Note: Another solution is to have stackable blocks.

Ruler

Procedure:

Each block will need a small loop to hook the spring scale to. An easy way to make such a loop for lighter blocks is to take a length of masking tape, attach one end to the block, crimp a length of the tape and attach the other end beside or over the other end on the block.

The masking tape loop will only work for pulling light objects. It does a good job for that and is easy to make.

Place a block on a smooth table top

Set the ruler so you can see how far you will move the block

Hook a spring scale to the block

It is important to pull steadily on the spring scale but reading the force can be difficult. Be sure to read it when the blocks are moving along.

Pull the block steadily for 30 cm

Observe the amount of force on the scale in grams

Note: If the scale barely moves, try a scale with a more sensitive scale on it.

Repeat this for each block or additional block

Observations:

Record the distance and force for each block

My wood scrap blocks were mostly flat pieces making them easy to stack for pulling.

Analysis:

Multiply the grams times the distance in centimeters for each block to get the work done for each block.

Conclusions:

Which block has the most mass? Why do you think so? [You can check this by massing the blocks.]

Do you do more work moving a block with less mass or more mass?

Each block added to the stack increased the amount of force needed to pull the stack.

If you pulled a block 15 cm, would you do more or less work? Why do you think this?

What I Found Out:

I used some scrap wood pieces for blocks so they came in various sizes and shapes. The biggest one was the one I chose to put the loop on. the others were piled on top of it one by one to increase the mass pulled by the spring scale.

The first block took 6 g to pull it the 30 cm. This made the work done 180 g-cm.

Two blocks took 40 g to pull the same distance. Now the work done was 1200 g-cm.

Three blocks took 49 g to pull. Now the work done was 1470 g-cm.

Four blocks took 52 g of effort making the work done 1560 g-cm.

Five blocks took 75 g of force making the work done 2250 g-cm.

Six blocks took 85 g of force making the work done 2550 g-cm.

Seven blocks took 90 g of force making the work done 2700 g-cm.

The last block was added to the stack. The pile was pulled for the 30 cm so work was done.

The more blocks on the pile, the more force it took to pull the pile across the table. That makes me think a heavier block will take more force than a lighter one.

Looking at the increases in effort, the first block took 6 g but the second took an additional 34 g so the second block must have more mass than the first one.

The third block increased the force 9 g and the fourth a mere 3 g. These are lighter than the second block.

The fifth block increased the force needed 23 g. The sixth added 10 g and the last one 5 g. The second block was the biggest block with the fifth block next.

Pulling the first block 30 cm required work of 180 g-cm. If I had pulled the block only 15 cm, it would be 6 g times 15 cm or 90 g-cm. It takes less work to move half the distance.

# Physics 7 Motion and Vectors

For the Projects we’ve done so far we’ve accepted that the paper, the car, the balls and the jar moved. What is motion?

Look up motion in the dictionary. What does it say?

My dictionary says motion isthe act of changing place or moving.

We used vectors earlier to show the direction of a force. Vectors can also help us show where and how far something is moving.

Another concept in physics is displacement. This is how far something moves from its original position. This is not the same as the distance something moves.

Question: How can vectors show how something moves?

Materials:

Sheets of Grid paper [quarter inch is fine]

Pencil

Procedure:

Draw a line across a sheet of grid paper about ten squares from the top

The line is a street

Make a little mark across this line every second square

These marks show blocks

Draw a little house at the middle mark on the line

On a map east goes to the right, west to the left, north up and south down.

Trip 1:

You leave the little house and walk three blocks east to the market

Above the line you can make a fancy house and market. Below the line is room for the vectors. The first one goes from the house east to the market. It has an arrow on the tip pointing the direction you walked.

To show this draw a line from the mark in front of the house three blocks east or and put a little arrow at the end of the line.

Now you walk three blocks west back to the little house

You now walk back home so the vector arrow goes from the market to your house. The arrow is now on the end at your house as you walked that way.

Draw another line from the market to the little house and put a little arrow on the end

Conclusions:

How far did you walk?

This is distance. Your total distance is 3 blocks east plus 3 blocks west or 6 blocks.

Notice on your graph the arrows are equal and opposite. The vectors say you did not go anywhere.

Displacement is how far something moves away from where it started. In this case the displacement is 0 because you started and ended at the same place.

Trip 2:

Draw another line about ten squares below the first line and put a little mark in the middle

The long green line is the street running east and west with a mark showing your house in the middle. You can draw houses above the line if you wish.

This time each square is a block

You go to a friend’s house five blocks west of your house

The first vector is you going five blocks west so the line goes five squares to the left.

Draw this vector

The two of you decide to go to another friend’s house seven blocks east of where you are

Going seven blocks east means going past your house plus another two blocks and the vector shows this.

Draw this vector

Later you and your first friend go to your homes for dinner

You go only a short distance and your friend keeps going so two vectors are needed. I labeled them with a y for you and an f for friend so i would know which was which.

Draw these vectors

Conclusions:

Trip 2:

What distance did you walk?

What distance did your first friend walk?

What distance did your second friend walk?

What is your first friend’s total displacement?

Observations:

Mark your home in the center

Walk the five blocks west to your friend’s house

[Hint: This may be easier if you use more than one color for the vectors such as one to you alone, one for you and your first friend, one for the three of you and one for your two friends.]

The two of you walk seven blocks east to your other friend’s house

The three of you go five blocks east to a park for the afternoon

The three of you go to your house for supper

Your two friends go back to your first friend’s house for the night

Conclusions

What distance did you go?

What distance did your first friend go?

What was your first friend’s displacement?

What distance did your second friend go?

What was your second friend’s displacement?

What I found Out:

I used four different colors and labeled the vectors to keep track of them. Another way would be to do three graphs, one for each person. That method would make it easier to see how far and where each person went.

I walked 5 blocks W + 7 blocks E + 5 blocks E + 7 blocks W or 24 blocks. My displacement was 0 because I started and ended at home.

My first friend walked 7 blocks E + 5 blocks E + 7 blocks W + 5 blocks W or 24 blocks.  My first friend’s displacement is 0 because of starting and ending at home.

My second friend walked 5 blocks E + 7 blocks W + 5 blocks W or 17 blocks. My second friend’s displacement is 7 blocks because of starting at home and ending at my first friend’s house.