Physics 13 Acceleration and Speed

All forms of motion involve either speed or acceleration. What is the difference?

Speed in physics is how far something moves in a given time.

Acceleration in physics is a change in speed or direction or both.

Straight line motion is an easy way to look at both acceleration and speed.

This Project is easier with two people.

Project materials

Question: What is the difference between speed and acceleration?

Materials:

Stopwatch

Meter stick

Ball

Short ramp 1 to 1.5 m long

Long ramp 4 to 5 m long

Tape

Marker

Procedure:

Make the two ramps [Plastic car track will work, if you have it. Mark the long ramp with masking tape.]

I used stiff cardboard because it is smooth, easy to get and easy to work with. My piece was over a meter square. I cut long strips of cardboard about 15 cm wide.

folding the ramp pieces

My cardboard was thick and stiff making folding difficult. The fold does need to be fairly straight. Fold up one end so the ends are the same then start folding. Start the fold at the other end the same way then move each fold up toward the middle of the piece.

One piece was folded in half lengthwise for the short ramp.

overlapping the long ramp pieces

Each piece for the long ramp overlapped the other by 10 to 15 cm to add strength to the joint. Each overlap had to have the same top and bottom overlap so the ball would always run from the top piece to the bottom piece to minimize friction.

Several pieces were taped together to form the long ramp. First fold each piece in half lengthwise. Each piece must overlap 10 cm or so. The top piece always overlaps the next piece. The folds must be in the same place at each overlap. Tape each one top and bottom.

outside taping on long ramp

Because the long ramp would tend to sag down, I put extra duct tape over the joint to strengthen it.

Mark across the long ramp 20 cm from the end. Make a second mark 1 m from the first mark.

taping the inside of the ramp

In putting the duct tape on the inside of the ramp, I put it in the fold first then smoothed it upwards.

Make another mark 20 cm from the second mark. The next mark is 1 m from the third mark.

marking the meter areas on the long ramp

I numbered each marked meter on the long ramp with the top one being one. Each meter did span one of the taped areas but duct tape is smooth and few if any wrinkles were in the area the ball ran down minimizing friction and allowing the ball to run freely down the ramp.

Go down another 20 cm and make another set of marks 1 m apart.

Set up the short ramp so the top is 50 cm off the floor. The floor must be smooth, not carpeted.

setting up the short ramp

Masking tape holds the ramp in place. Tape keeps the ramp straight so the ball will go straight. The meter stick was moved after this as the ball hit it instead of going by.

Set the meter stick on the floor 10 cm from the end of the ramp so the ball will go past it

Get ready with the stopwatch

Let the ball go down the ramp and time how long it takes the ball to go the 1 m  past the meter stick

Do this three times

Move the meter stick so the end is 1 m from the end of the ramp

Time how long it takes the ball to go past the meter stick at least three times

Move the meter stick so the end is 2 m from the end of the ramp

Time how fast the ball goes past the meter stick at least three times

Set the long ramp up so the top end is 50 cm off the floor [If the ramp sags anywhere along its length, prop it up.]

setting up the long ramp

The long ramp was not quite straight. Only one prop was under it so the bottom sagged too much. It tried to tip over and required additional taping to the floor.

Get the stopwatch ready

Time how fast the ball goes the first meter at least three times

Time how fast the ball goes the second meter at least three times

Time how fast the ball goes the third meter at least three times

Place the meter stick on the floor 10 cm from the end of the ramp

Time how fast the ball goes this meter at least three times

Observations:

Short ramp-

1st meter:

2nd meter:

3rd meter:

Long ramp-

1st meter:

2nd meter:

3rd meter:

Floor meter:

Analysis:

Calculate the average time for each set of times for the short and the long ramps.

Draw a graph of time and which meter was run for the short ramp

Draw a line through the times

Add the times for the long ramp to the graph

Draw a line through the times

graph of times

The times from the short ramp for the different meter placements were very similar. They did gradually increase but all stayed between .3 sec and .38 sec giving a fairly straight line on the graph. This indicates we were measuring speed. The times from the long ramp changed a lot for the different meter sections giving a steeply curved line on the graph indication we were measuring acceleration.

Conclusions:

Does the speed of the ball seem to change for the short ramp? Why do you think so?

ball and short ramp

The ball sped down the short ramp and past the meter stick almost faster than I could start and stop the stopwatch.

Does the speed of the ball seem to change for the long ramp? Why do you think so?

Are you measuring speed or acceleration for the ball and short ramp? Why do you think so?

Are you measuring speed or acceleration for the ball and long ramp? Why do you think so?

If you could time the ball for the top and bottom halves of the short ramp, would the times be the same? Why do you think so? Is the ball accelerating on the short ramp?

Does the length of the ramp matter to the final speed of the ball? Why do you think so?

What could cause the ball to slow slightly from the short ramp?

 

What I Found Out:

I missed having Aiah to help with this Project. Two people working on it makes this much easier.

The short ramp was quick and easy to make and set up. My ball passed the first meter in .34 sec, .38 sec and .28 sec for an average of .33 sec. The ball ran the second meter in .41 sec, .25 sec, .31 sec and .28 sec. for an average of .31 sec. This was the hardest meter for me to time. The times for the third meter were .40 sec, .31 sec and .37 sec for an average of .36 sec.

The three average times for the short ramp were very similar. The speed does not seem to change for the distances from the ramp. This would be a measure of speed as the ball travels at about the same rate in the same direction.

The long ramp was harder to assemble. Duct tape holds it but I had to use a lot of it to keep the pieces from pulling apart. The prop under the ramp keeping it from sagging helped hold it together too.

ball on long ramp

The ball ran much slower down the long ramp making it easier to take a picture but the ball went faster for each meter and was going at the same speed when it got to the bottom as it had from the short ramp.

The first meter was the hardest to time for the long ramp. My times were .97 sec, .94 sec and .90 sec for an average of .94 sec. The times for the second meter were .59 sec, .56 sec and .50 sec for an average of .55 sec. The third meter times were .47 sec, .40 sec and .46 sec with an average of .44 sec. When I timed the meter on the floor, the times were .31 sec, .41 sec, .44 sec, .34 sec and .41 sec with an average of .38 sec.

While the ball is going down the long ramp, it goes faster each lower meter. The time it takes for the meters gets shorter so it must be going faster. This would be a measure of acceleration because the ball’s speed is increasing or changing.

If I could time the ball going down the short ramp, the ball would go faster on the bottom half of the ramp than on the top half. I think this because the ball has no speed when I first let it go and it is going very fast when it gets to the bottom. The ball’s speed is changing as it goes down the ramp so it is accelerating.

When I compare the average speeds of the ball for the first meter covered on the floor for the two ramps, they are similar. Even though the ball went much farther to get down the long ramp than on the short ramp, it accelerated the same amount. The length of the ramp does not matter.

What does matter is friction. This gradually slows the ball down as it rolls across the floor.