Teaching Guidance for 14-16
Galileo was interested in predicting how bodies move. He allowed an object to roll down and up a curved track, and showed that it rose to roughly the height from which it was released, regardless of the shape of the track.
Galileo recognized that, unfortunately, the experiment was marred by the effects of friction.
Experiment: Demonstrate Galileo's rolling ball
Scientists seek to demonstrate phenomena clearly. They try to eliminate any undesired external influences (in this case, friction), in order to show an underlying principle.
Galileo went on to use a pendulum to demonstrate the same phenomenon. He believed that this would be even less affected by friction.
Experiment: Set up a simple pendulum
Demonstrate how it swings.
Experiment: Demonstrate Galileo's pin and pendulum
In fact, the idea of the conservation of energy was far in the future when Galileo described and explained his experiment. Instead, he talked in terms of momento and impeto. These terms correspond (more or less) to what is now called momentum.
Later, Newton also used the idea of momentum, which he regarded as the fundamental property of a moving object. The idea of kinetic energy was not established until the mid-19th century, 200 years after Galileo's death.
Ideas like that of energy, which scientists today take for granted, are not self-evident. Both momentum and kinetic energy were identified when people realized that they were conserved quantities in certain situations.
We are grateful to David Sang, author of this Case Study.