 In Galileo's doomed experiment at the Leaning Tower, it turns out he was right all along. Different masses should indeed fall at the same rate, or have the same acceleration, in the absence of air resistance. The spectators completely misunderstood the true reason why the feather fell slower, which was because of air resistance and not because it had a smaller mass. Scenes at the church and at the Leaning Tower. Mention is made of Aristotle's law of nature. What is it and why is it incorrect? Can you think of any better laws? I'll give you a clue. One character in the film can't stop going on about them. Aristotle's law of nature says that heavy objects fall faster than light ones. Although our everyday experience seems to suggest this, in fact careful experiments easily disprove it. So Aristotle's law is a bad law or not a true law of nature at all. Newton's laws however are better because they explain many different things. Can be tested and make successful predictions. But on earth they're not common sense. Things just don't keep moving in a straight line at constant speed without a source of power. But Galileo have been better off rolling the balls down a slope, as Alfonso suggested. The balls would be moving slower, so surely it would be easier to see what was happening. What are the pros and cons about doing it this way? Think about what's actually happening when the ball is rolling instead of free falling. Have a go yourself to find out. Using rolling balls will slow down the motion, so it should be easier to time. I'll be using a ruler to start them off together. How about that Amy? When the balls roll down the slope, some of the energy of the ball that would normally make it accelerate fast is being used to make it rotate. So the effect is the ball rolls slower, or more precisely it accelerates slower. If we were to use say a can of drink and a can of solid food, we might even bear to tell the difference between the two. But overall we can conclude that this experiment definitely shows that Galileo was right. Different masses roll down the slope at the same rate. To improve on Galileo's experiments of dropping weights with all modern day technology at our disposal, how could we actually measure acceleration, rather than just showing that different balls of different mass reach the ground at the same time? Today we could use electronic timing to improve upon matters in Galileo's time, or perhaps a very high-speed video camera. However, for this demonstration, we're actually going to use something a little different. We call this machine Sparky because with the aid of a power source over here and a metal ball, we're going to be able to create sparks between this wire and a length of special paper. These sparks will be made 50 times a second. Now that means to say that when we examine the paper trail after the ball has landed, every spark will have been separated by a time of one-fiftieth of a second, and by making measurements with a ruler we can determine the acceleration of the ball. Okay, let's give it a go. First start the sparks, press the button. How about that then? What would have been the results if Galileo had dropped his weights under feather on the moon? There are two differences, Amy. They both fall together on the moon because they have the same acceleration. That's because there's no air resistance, but they are both much slower than on earth because of the lower gravity. A very similar experiment has actually been carried out and filmed on the moon by the Apollo 15 astronauts. They used a hammer and a feather. Well, in my left hand I have a feather, in my right hand a hammer, and I guess one of the reasons we got here today was because of a gentleman named Galileo a long time ago who made a rather significant discovery about falling objects in gravity fields. And we thought that where would be a better place to confirm his findings and on the moon? And so we thought we'd try it here for you. The feather happens to be appropriately a falcon feather for our falcon. And I'll drop the two of them here and hopefully they'll hit the ground at the same time. How about that? Well, we knew that Mr. Galileo was correct in his findings.