To collide means to crash into something with force. When two cars collide at an intersection, they smash into each other. When a soccer player collides with a goalkeeper while racing for the ball, they both end up tumbling to the ground.

A collision happens when things are moving toward each other or when one moving object strikes something stationary. Asteroids collide in space, creating spectacular bursts of light and debris. Football players collide on the field. Even ideas can collide: when two strong opinions meet head-on in a debate, people might say the ideas collided.

Scientists use the word precisely: in physics, a collision transfers energy from one object to another through impact. When billiard balls collide on a pool table, the moving ball transfers its energy to the stationary one, sending it rolling across the felt.

The word suggests suddenness and force. You wouldn't say two people collide if they gently bump into each other in a hallway, but you might if they're both running around a corner and slam into each other unexpectedly.