The case of falling bodies project

B) Teaching with Experiments

This is an experiment with everyday materials that is based on an experiment described in Galileo’s work.

In order to perform the experiment we need the following materials:

A) Six empty plastic bottles of water or any other refreshment with a size able to contain 1.5 – 2 litres of liquid cut at their upper part in order to form plastic tubes that have the same height.

B) Water , olive oil and alcohol (about four liters of each liquid).

C) Two table tennis balls that are filled with tinny metal shots in order to weight 36,5 gr and 47 gr. We make a hole at each ball and through the hole we put tiny metal shots inside the ball and we weight the ball on a platform scale till we get the above weights and then we close the hole with glue and let it dry.

Now we are ready to perform the following experiment:

We fill two of our plastic tubes with water, two of the plastic tubes with olive oil and two of them with alcohol. We put the light ball under the water in the first tube and the heavy ball under the water in the second tube and we let them drop in the water simultaneously and from the same height. The heavier ball reaches the bottom first. We see it happen and we also hear the sound of the hit on the bottom of each ball.

Then we put the light ball under the olive oil in the third tube and the heavy ball under the olive oil in the fourth tube and we let them drop simultaneously and from the same height. The heavier ball reaches the bottom first. We see it happen and we also hear the sound of the hit on the bottom of each ball. But the time between the two hits is much sorter than previously when both balls fell in water.

Then we put the light ball under the alcohol in the fifth tube and the heavy ball under the alcohol in the sixth tube and we let them drop again simultaneously and from the same height. The heavier ball reaches the bottom first. But right after the light ball also reaches the bottom. The time between the two hits is even shorter this time.

Then we let the ball fall from the same height in the air and the two balls reach the ground at the same time.

This experiment offers the opportunity to discuss about the effect of the medium on the way various weights fall. In everyday life we see items of different weights when let fall from the same weight to reach the ground not at the same time but first the heavier ones hit the ground. If there weren’t the medium (the air, the atmosphere) and the fall was taking place in vacuum all bodies let fall from the same height would touch the ground at the same time. Galileo thought of an experiment that would make people aware of the effect of the medium. This experiment with everyday materials is based on Galileo’s work. In our experiment we focus on the time interval between the hits on the bottom of the bottle-tubes of two balls with different weights. The lighter the medium the shorter this time interval is and in the air the two balls hit the ground simultaneously.