Galileo’s Gravity Lab

There is an apocryphal story of Galileo dropping cannon balls of unequal mass from the leaning tower of Pisa, in PisaItaly. According to the story the crowdwas astonished that the balls hit the ground at the same time. Although the story may not be true, Galileo did scientifically measure the rate of objects of different mass falling to Earth and found they all accelerate at the same rate! This finding went against 2000 years of teaching by the Greek scholar Aristotle who said that heavier (more massive) objects hit the ground first. It is surprising that it took so long for someone to actually test and scientifically refute Aristotle’s erroneous claim about heavy objects and gravity, and that is why Aristotle’s myth still persists in the minds of many today!

In this lab you will approximate what Galileo did to test Aristotle’s claim that objects of variable mass fall to earth at different rates. Galileo did not simply drop objects of varying mass and measure when they hit the ground. Instead he rolled balls of varying mass down a track and measured how long it took to reach the end of the track.

Which ball will hit the table first if you roll a golf ball and a ping pong ball down a track? Write your hypothesis below:

Place one end of your track on top of one book. First roll the golf ball 3 times down the track and then the ping pong ball 3 times down the track. Time how long it takes the balls to hit the table. Record your times below and average your times for each ball.

Time for Golf Ball in seconds / Time for Ping Pong Ball in seconds
Average Time for Golf Ball = / Average Time for Ping Pong Ball =

Galileo polished his tracks to reduce friction and elevated is tracks to different heights. Prop another book under your track so it is two books high and repeat your experiment.

Time for Golf Ball in seconds / Time for Ping Pong Ball in seconds
Average Time for Golf Ball = / Average Time for Ping Pong Ball =

Was your hypothesis correct?

Explain your conclusion based on your data.

What force was Galileo trying to reduce by polishing his tracks?

Now find the force of gravityon each ball in Newtons. In fact that force of gravity on each ball is the weight of each ball in Newtons. Weight is measured in Newtons! Weight in Newtonsis the measure of the force of acceleration due togravity(on Earth acceleration is 9.8m/s2) on an objects mass.

The weight of each ball is its mass in kg times the acceleration due to gravity

Here is the equation again: Weight in Newtons (N) = kg x 9.8m/s2

Show your work below by plugging in your values into the equation.

Weight of golf ball______Weight of ping pong ball ______

The acceleration rate that an object experiences on Earth (9.8 m/s2) is directly proportional to the mass of the Earth. The Moon has 1/6 the mass of the Earth and therefore accelerates objects only 1/6 as much as it does on Earth. What would be the weight of the golf ball and the ping pong ball on the Moon? Show your work below!

Weight of golf ball on Moon______

Weight of ping pong ball on Moon______