Galileo's Tower of Pisa Experiment

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Air Temperature 20° C, 1 atm pressure
Luciano Troilo, created with GeoGebra


Check the following two hypotheses:

  1.  Aristotle: An object falls with a speed proportionate to its weight that is, the heavier the object, the faster it falls.

  2. Galileo: The rate of fall caused by gravity is the same for all objects.



Fix the diameter of the ball and measure the time of fall for various values of the mass. For example, mass from 10g to 10 kg
Fix the mass of the ball and measure the time of fall by changing the values of the diameter. For example, D: 10cm to 100cm


Transfer the experimental data to an Excel spreadsheet and analyse the results.

Click here to download and see =>Example xls file

What can you infer from these experiments? (Refer to THEORY section)


Check Galileo's Law of Falling Bodies

The distance traveled by a falling body is directly proportional to the square of the time it takes to fall.
Measure the falling time each 10 meters. Repeat the measurements 3 times.

Use an Excel spreadsheet to analyse the results.
Click here to download and see =>Example xls file





Experiment with these balls/objects

Ball/Object Diameter (cm) Mass (kg)
billiard ball 6.12 0,210
Metal ball 7.5 0.720
biglia di vetro 1.6 0.003
pallina di piombo 0.2 3e-5
palla di piombo 22 35.4
palla di legno (pino) 22 1.25
Soccer ball 22 0.430
basket ball 24.8 0.570
beach ball 27 0.180
balloon 22 0.01


In the period before Galileo, scientists thought that force causes speed, as claimed by Aristotle. Galileo showed that force causes acceleration. On the basis of the law of parabolic fall, Galileo reached the conclusion that bodies fall on the surface of the earth at a constant acceleration, and that the force of gravity which causes all bodies to move downward is a constant force. In other words, a constant force does not lead to constant speed but to constant acceleration. Galileo's claim that force causes acceleration is inseparable from his claim that bodies do not require a cause to continue their movement. This latter claim states that a body in motion will continue its motion so long as no factor disturbs that motion. This principle is called the principle of inertia.

The law of parabolic fall was an innovation in that it claimed that the speed of a body will continue to increase endlessly. Contrary to the claims of the natural philosophers of his period, Galileo claimed that a body will not attain a certain speed which will remain constant but will continue accelerating until it comes into contact with the ground.
This claim is of course true so long as one ignores air resistance, which can be very significant for certain bodies and at high speeds.

it is important to remember that Galileo's law of fall claims that bodies fall at a constant acceleration, i.e., that their speed increases by equal increments within equal time periods, and that the distance traveled by them in equal time periods is not equal.
For example: A falling ball, in the second second of its fall, will travel a distance three times as great as the distance it traveled during the first second; in the third second it will travel a distance five times that of the first second; in the fourth second it will travel a distance seven times that of the first second.




UNDER CONSTRUCTION ( please insert here some problems and/or exercises


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