 Greetings and welcome to the Introduction to Astronomy. In this week's Misconception in Astronomy, we are going to look at the idea that heavy objects fall faster than lighter objects and see why this is generally not true. So let's look at what we know about gravity and these types of objects. So first of all our quick answer is, do they fall faster? No. Under gravity, all objects will fall at the exact same rate. So it doesn't matter if you have a very large object here and a very small object, and let's say that this is a large mass, let's say this is 10 times the mass of the smaller one. They would still fall and strike the ground at exactly the same time. So if this took, say, 5 seconds to hit the ground, then guess what? This one is going to hit the ground in 5 seconds as well. It does not matter what their mass is. Now why is this often a misconception? We know that if we drop a rock in a piece of paper, they're not going to fall at the same rate. That the rock is going to hit the ground first. But it's not because of its mass. It is because of our atmosphere. Lighter objects will have a larger air resistance. So there is an additional force acting in addition to gravity. We don't just have gravity acting here. We have also the air resistance. And the air resistance will work stronger on a lighter object and stronger on an object that is more spread out. Now you can do this experiment yourself. If you take, say, a book and a piece of paper and drop them at the same time from the same height, you will see that they do not hit the ground at the same time. Take that same piece of paper and crumple it up and drop them again from the same height and you will see that they do strike the ground at the same time. It is not that the mass is different because you did not change the mass of the paper by crumpling it. All you did was change its shape and make it less subject to air resistance, making it fall at the closer to the rate that it should. So for example, and one of the famous examples would be Galileo when he supposedly did the experiment from the Leaning Tower of Pisa and dropping a wood ball and a iron ball from the same point and letting them both fall and finding that, yes, they strike the ground down here at exactly the same time. Now what would there have been a slight difference? Yes, the lighter ball would have felt more air resistance and would not have fallen as quickly, but you would not have the significant difference that you would expect under the physics that held at the time. So we found that, yes, under gravity all objects fall at the same rate. So how can we test this? Well here on earth we could do it in a vacuum chamber and see how objects fall, but we can also do this experiment on the moon. And this was done by the Apollo 15 astronauts and we can go ahead here and watch the clip showing when they dropped a hammer and feather at the same time on the surface of our moon. 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 than 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? Now you notice there that yes they hit at the same time, also note how slowly they fell. Not only do they fall at the same rate but they fall slower on the moon than they would on earth because the moon has a lower gravity. So let's go ahead and finish up with our summary here and what we've looked at is that all objects in a gravitational field will fall at exactly the same rate so every object will fall at exactly that same rate. Air resistance in the atmosphere can slow down the lighter objects, however as we saw in the video clip on the moon a hammer and feather will fall at the same rate on the moon in the absence of the air resistance of an atmosphere. So that concludes this lecture on heavy objects and light objects falling. We'll be back again next week for another misconception in astronomy. So until then, have a great day everyone and I will see you in class.