Galileo Inclined Plane Experiment

Student Instructions

Drop a few balls and see how they speed up as they fall further and further. Now let some balls roll down the ramp and note how their speed changes as they get further down the ramp. Why do you think Galileo used the ramp to measure the rate instead of dropping objects? Why do you think rolling balls down a inclined plane tells us something about how objects fall?

1. Measuring the Rate of Acceleration, Method 1: In this method you will measure the distance traveled by the ball by marking the position of the ball at equal intervals as measured by a pendulum. Can you think of any other way of measuring equal intervals. Galileo used his heartbeat and a water clock, as well as a pendulum?

Setup:

1.Prop the inclined plane up by just a few books or pieces of wood. You want the ball to roll slow enough to measure, but fast enough so that it starts and rolls freely.

2. Position 4 or 5 people along the ramp with markers and have one person watch a pendulum. The person at the pendulum will call out start at the beginning of a swing and then call out 1, 2, 3 etc. as each subsequent complete swing of the pendulum is completed. The ball will be started when the timer says start and then each time a number is called out a student will mark the position the ball was in when they heard the number.

3. You can then use the string to measure the distance between the marks. Use the first distance as the unit with the string and see how many units long each of the other distances is. If you want, calculate how many multiples of this unit each of the other distances are. Then figure out the total distance traveled at each point (add up all the distances up to each marker):

Time	1(start to marker 1)	2 (marker 1 to 2)	3	4	5	6
Trial 1 Distance	1 (use this as unit)
Trial 2 Distance	1 (use this as unit)
Multiples of unit	1
Total distance	1

2. Measuring the Rate of Acceleration, Method 2: In this method people will call out as the ball passes them and you will try to arrange the people so they call out in a regular pattern with equal periods of time between them. Galileo knew from his music studies that human can recognize deviations from a pattern up 1/64^th of a second.

1. In this method 5 or 6 people will start by position themselves at equal intervals along the ramp holding their finger as a marker near the ramp to mark the equal intervals. The ball will be released and each person will call out as the ball passes their finger. What is the pattern of the calls when you are spaced equally?
2. Now try spacing yourselves to make the pattern of your calling out more regular. You may have to experiment a little or you may be able to figure it out by thinking about it. Once you arrange yourselves so that the calling out is perfectly regular, making equal intervals, have each person mark where their finger is and measure as in the previous trial.

Time	1(start to marker 1)	2 (marker 1 to 2)	3	4	5	6
Trial 1 Distance	1 (use this as unit)
Trial 2 Distance	1 (use this as unit)
Multiples of unit	1
Total distance	1

Do your two methods give the same results? If not, can you figure out which might be more accurate.

Galileo found that the distance varied with the square of the time? Did you get this result? If not, does this prove Galileo wrong? Why do you think your result might differ from his? How could you prove him wrong in an experiment of this type? How could you prove him right?

3. Different Weight balls. Galileo did not use this experiment to prove that heavy objects fall at the same rate as light objects See if you can figure out why.

Roll two balls of different weights down the ramp at the same time? Which is faster? Try some different combinations? Do your results prove that heavy objects fall faster? Air resistance isn’t as much a factor on the ramp. What other explanations can you think of for the results? Under what conditions can you imagine heavy and light balls rolling down at the same rate?