Galileo performed a famous experiment where he dropped two objects of different mass from the top of the Leaning Tower of Pisa and he showed that they hit the ground at the same time. And this demonstrated that the acceleration due to gravity is independent of the mass of an object. But he didn’t just do that experiment; he also showed this in a more laboratory condition by rolling objects down a slope.

So we’re going to try and reproduce that kind of laboratory experiment and show that if I have two cars here, if I roll these two cars down this slope, that it takes the same time to reach the bottom of the slope. And we have somebody here to catch the cars when they get to the bottom so that there’s no dangerous collisions.

Okay, so now I’m going to start off with a car without any weights on it. So this is the light one. So when I release this…

[sound of car rolling down]

Okay, now I have the same kind of car, different colour, but with four masses on it. In fact I have a kilogram on it. So there’s a substantial difference in the mass of the two cars. So I’m going to release it and we’ll see how long it takes to reach the bottom. So, three, two, one…

[sound of car rolling down]

Okay, so that shows that there’s not a dependence on the mass of the car, because this one weighs a lot, lot more than the other one.