The boulder refuses to budge. Around it are the words: "Every body perseveres in its state of being at rest or of moving uniformly straight forward except insofar as it is compelled to change its state by force."
In other words, stuff that's not moving won't move unless something moves it. Stuff that is moving won't stop unless something stops it. Weird to think that people used to really not know that, right?

Over the elephant are the words Force = Mass x Acceleration. In other words, the strength of a force depends on how big and fast the thing that's applying the force is.

Where the elephant is bracing himself against the ground are the words: "All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction"
So when you apply force to something, you get an equal and opposite force right back at ya.