You’re sitting in a train, and another train next to you starts moving. You feel like YOU are moving, but you’re not. What concept explains this feeling?
relative motion
Your dog is chasing the mailman down the street. To describe how fast and in which way the dog is running, you need to know its:
Velocity
You throw a ball straight up in the air, and it comes right back down. What invisible force is responsible for this?
Gravity