Question: How fast does a particle have to be moving to collide with another?

Lucy Budge answered on 21 Jun 2019:

Particles collide with each other all the time, they don’t have to be moving quickly! In fact the reason you don’t fall through your chair/the floor/the earth is because of particles colliding with each other!

The atoms everything is made of have electrons around the outside of them, and since electrons are negatively charged (and like charges repel) the atoms repel each other and stop you falling!

(as an aside, this doesn’t work with the air because there are too few atoms to stop you).

In particle physics though we want to see what happens when they have loads of energy and are moving really quickly! So we get them as close to the speed of light as we can – since this is the “speed limit of the universe” (nothing can go faster).

The speed of light is nearly 700,000 miles per hour!