Physics can be one of the hardest sciences to learn. Although the math scares off some students, others just get stuck in the fact that so many laws of physics are not observable on Earth. We learn the law of inertia, which states that objects in motion stay in motion. But, when we roll a ball, it does not stay in motion. Rather it stops, sometimes sooner rather than later. We learn that gravity operates on all objects with the same force, regardless of weight, yet we see that a piece of paper will flutter to the floor much more slowly than a pencil. So, physics, what gives?
Of course, further study of physics will tell you that friction causes the ball to stop rolling and that air resistance keeps the paper from diving to the ground, despite gravity's best efforts. And, the explanations make sense, but they are still hard for a beginning physics student to process.
That's why it's so fun to see that Galileo's (likely apocryphal) experiments, dropping feathers and cannonballs off of the Leaning Tower of Pisa, were recreated hundreds of years later on the Moon - an environment that, as a vaccuum, eliminates those pesky air resistence problems. The astronauts on 1971's Apollo 15 mission dropped a feather and a hammer on the Moon to test the theory that Galileo developed in 1589: do items of different masses drop at the same rate? They do.
Learn more about Galileo here:
And, for a more kid friendly version, read our nest Idongetit Science Tale -- which take place, you guessed it, on the Leaning Tower of Pisa!