# Movable Walls

However, let’s imagine that we have a wall that is only 500 times as massive as an air particle. And let’s imagine that the wall is sitting on a sheet of very, very, very slippery ice and can move freely. If an air particle were to bounce off of that wall now, what do you think would happen?

Woo hoo! When the particle bounces off of the wall, it exerts a force on the wall and pushes on it. This push gets the wall to start moving slowly to the right. If the ice is slippery enough and there is no friction or air resistance, the wall will actually keep moving to the right until something else stops it.

Let’s say that we want to push on the wall even harder. There are only three ways that we can increase the force on the wall. The first way is to increase the speed of the air particle. The faster the particle, the greater the force.

The second way is to increase the mass of the air particle. The more massive the particle, the greater the force.

The third way is to increase the number of collisions. While the push from each individual air particle may be very small, all of the pushes add up and the collective push can be very large. The more collisions, the greater the force.

Notice that when we increase the speed of the air particle, the mass of the air particle, or the number of collisions, the force on the wall gets greater and it moves to the right faster than the first wall did at the top of the page.

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