# Measuring the Force of Collisions

Just like we can measure the weight of an object (how hard the Earth is pulling on it) with a spring, we can also use a spring to measure the force of collisions. Let’s revisit our movable wall, but this time, let’s put a spring behind the wall so that we can measure the force pushing on it.

As you can see, the force from a single particle barely registers on the spring. The force from a superfast particle and the force from a supermassive particle both compress the spring about 0.2 units. And the force from a superfast, supermassive particle compresses the spring about 0.8 units.

You should also notice that the force from a collision is very brief. This is different than the force of gravity, which is continuous. When thinking about the force of particle collisions, in general, we are not going to be thinking about single collisions; we are going to be thinking about lots of collisions happening over time. So in that kind of situation, there are three variables for us to consider: particle speed, particle mass, and the rate of particle collisions. The rate of particle collisions is the average number of collisions that occur in one second.

In the simulation below, adjust the three variables to see how they affect the force pushing on the wall:

As you can see, the force on the wall is proportional to the rate of particle collisions. If the rate of particle collisions doubles, then the force on the wall will double.

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