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.

**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

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

**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.