Dynamical friction

You know how sometimes, when you are playing with your friends at the playground or at the park, and you try to catch them while they are running away from you? It can be harder to catch them when they are moving fast compared to catching them when they are standing still, right?

Well, imagine if you were a big ball of gas or a star in space, and there were a lot of smaller particles, like dust or rocks or other small stars, that were also moving around in space. When you move through these particles, it can make it harder for you to keep moving in your original direction, just like it's harder to catch your friends when they are moving fast. This is called dynamical friction.

The smaller particles that you are passing through will exert a force on you that slows you down. This happens because as you move through the particles, some of their momentum is transferred to you, pushing you in the opposite direction. This force becomes stronger as you move faster through the particles or if there are more particles present.

So, if you are a big star moving through space and there are a lot of smaller particles around, you will feel this force pushing against you and slowing you down. This means that you might not be able to move as far or as fast as you originally planned.

Dynamical friction can also cause stars or other objects in space to cluster together over time. This happens because as the objects move through the particles, they slow down and start to orbit around each other. Over time, their orbits can become more and more circular, which means they will stay closer together, like how you and your friends might huddle together if you are scared or cold.

So, just like when you play and run around with your friends at the park, moving through space can be affected by the particles around you. Dynamical friction is the force that makes it harder for big objects in space to move through all the smaller particles around them.