 We're going to be looking at collisions where the objects stick together during the collision. Now I'll demonstrate the collisions and get some data and later you'll use that data in order to determine whether momentum and kinetic energy are conserved in these collisions. We're using the same setup as in the past, a low friction track. The track has been leveled so that the gliders don't have a tendency to drift one way or the other. They move along it with fairly low friction, but they will slow down a little bit. So it's not completely frictionless. On each glider there's a post-it note which is taped there. And the purpose of the post-it note is to trigger the photogate timer as it passes through. And that's how we measure the velocities of the carts. And you may have noticed it was a little bit difficult to pull these apart. The reason they stick is because there's Velcro on the front of them. I don't know if you can see it, but there's a piece of Velcro on each side and the opposite kind on each side of this one. And so they will stick. So for each collision one cart is going to be stationary to begin with. I'm going to make it this cart right here. So it'll sit right there just in front of one photogate and this cart just to the outside of the other photogate. The reason I chose the position like this is almost immediately after the collision occurs this post-it note will pass through the photogate. So if there is any slowing down of the cart's due to friction it's not going to have time to slow down very much after that collision. So that minimizes the error due to friction. And for the same reason this photogate is close to the other one so that almost immediately after this post-it note passes completely through it collides with the other cart. In fact I can probably move that just a little bit closer. So that will minimize the error due to friction and we should get better data. So I'll begin by zeroing both of the photogates and position this and give this a push. And let's see what the photogates read. This one is .158 seconds and this one is .077 seconds. Alright well now what I'm going to do is put different amounts of mass in the carts and get some more data. So I'll take one of these bars. Now each bar is half of a kilogram and each of the carts is half of a kilogram. So that makes this cart now one four kilogram with the load on it. This one is still a half. Get that one ready. Reset the photogates. Here it goes. So the time readings are on this one 0.110 seconds and on this one 0.070 seconds. Alright let's change the bar to the other cart. So now this is one kilogram. This is half a kilogram. Reset the gates. Collision number three. Now that one you can see slowed down quite a bit. There might be a significant influence due to friction that you have to worry about. Okay the time on this is .239 seconds. And on this one is 0.071 seconds. Now you may have noticed that this flag was going through the photogate too. So this flag went through first and then it was followed by that one. And why doesn't this flag simply add to the time that was already there and give us an incorrect reading. The reason is that the timer actually will stop after the first photogate goes through and it will not record the time for the second flag. It will keep that in memory so if we wanted to find out what it was we could find out. But it doesn't actually display that. So that's how we can get away with that. Okay I'm going to put another bar on this cart and move this bar over to here. So now this is a kilogram and a half. This is half a kilogram. This cart is three times the mass of that one. Alright reset. And the times are .109 seconds. .078 seconds. Let's do one more collision. I'll take my last bar and put it on this one. So now we've got a kilogram here. Kilogram and a half there. Reset. And the times are .159 seconds. And .087 seconds. So with the data that you have the times for each collision and the width of the flag which by the way is 5.0 centimeters or .050 meters and the masses of the carts you'll be able to determine whether momentum and kinetic energy are conserved in these collisions.