Alright, I'm going to use these frictionless carts to show you three experiments. Before we get started, I just want to demonstrate that if I let go of the cart, because it has a string and it has this mass hanging here over the frictionless pulley, that the cart does accelerate. Now for the next demonstration, I want to take two carts that are identical and then pull on them with different amounts of force. So let me set that up. Alright, so the cart further away from you is going to have three times as much force pulling on it. So let's look to see if they accelerate the same, even though this one has three times as much force. Clearly, the cart in the back that had more force exerted on it horizontally, had a greater acceleration. Now, going to switch so that they have the same force acting on them. But one of the carts has more mass. So the cart further away from you has more mass, but both carts are being pulled with the same force all force. So let's see if they accelerate the same now. They both did accelerate, both carts accelerated, but they did not have the same acceleration. And finally, the third trial, I'm going to take this cart here, which has less mass. I'm going to pull on it with a small force and then this cart back here has more mass, and I'm going to pull on it with a bigger force. We'll see what happens. So they have the same acceleration in that case. Now, doesn't mean that that would always happen. There's lots of different ways I could do this. I could repeat that one, do a variation. So the same generic things are true. This one still has more mass and more force, but that one that I showed you, this is just a special case where you have just the right amount of force and mass so that they accelerate the same.