Written Narration:Secrets of the Universe

Relativity is what things are doing depends on how it is being seen.  If you are traveling in a car which speed is 50 kmh.  You toss an apple forwards, it travels at 60 kmh, but if you toss it the opposite direction, it will travel at 40kmh.  That's why athletes take a few steps forward before they toss the ball.  Energy also has mass, more energy has heavier mass.