Suppose a bug is sitting on a plane. To someone right next to the bug, the bug appears to not move, but a man from the ground would see the bug going as fast as the plane. It is relative, meaning it appears different to two different people.
It means that all motion is "compared to ..." something.
-- When you're reading a book on an airplane, the book is not moving compared to you, but it's moving at more than 400 mph compared to someone on the ground.
-- When you're riding in a car, the driver isn't moving compared to you, but he's moving at 30 or 40 mph compared to a person standing on the curb.
You might ask: "But how fast is the book REALLY moving ? How fast is the driver REALLY moving ?"
The answer is: There's no such thing as "really" moving. ALL motion is relative to (compared to) something.
If you want to touch off an explosion and watch somebody's face turn red, green, and blue ... some rainy afternoon when there's not a lot going on ... tell this to somebody who believes the Earth is flat and is willing to fight to keep believing it.
Formula for velocity: V(t) = Vi + at Where V(t) is velocity at time t, Vi is initital velocity, and a is acceleration. Solving for a: V(8) = Vi + a(8) V(8) = 0 (car has stopped) 0 = 24 + 8a -24 = 8a a = -3 m/s/s
