Newton's third law of motion states that for every action there's an equal and opposite reaction. So you cannot do something, you can't have an action, without there being some sort of reaction to it. So a really common way to look at this is to think about a rocket. So a rocket is projected forward by first pushing downwards. So you've got the rocket engines firing downwards and then the opposite reaction-- that's the action-- the opposite reaction is to push it and thrust it out into the atmosphere, out into space. So that's a very big example, but an everyday example of Newton's third law of motion-- for every action there's an equal and opposite reaction-- would be something as simple as walking, or skipping, or jumping. So think about that. What is the action and what is the opposite reaction? So the action would be-- if you're walking or skipping-- would be pushing. Pushing against the floor or pushing against wherever you're walking. And then the opposite reaction would be being projected forward, or in a jump being projected upwards.