Opening comedy clip talks about how some scientists are busy curing cancer, but others have seen fit to develop the seedless watermelon. Jerry sarcastically refers to the tremendous benefit conferred on consumers because of this. So why do some scientists do things like this? Because it's what consumers want!
Through a cartoon movie, Beakman explains why your stomach feels weird on a roller coaster and why the biggest hill is the first one. He hangs a bowling ball from the ceiling with a cable and then swings the ball to squish a watermelon (energy in and energy out). He then puts himself where the watermelon was and shows that the ball can't swing any farther than the point at which he lets go. Beakman goes on to explain that centripetal force prevents us from falling out of the roller coaster and demonstrates it. He uses a tray containing a glass of milk and a cupcake and quickly spins it around to show that nothing falls off. He then explains why inertia keeps us from falling to the ground and brings all of the concepts together.
Beakman sticks pencil "people" into a watermelon to demonstrate that each "person" can say they are going to the bottom of the earth from where they are "standing" but there is no real "bottom" of the earth. There is no up or down but it depends on how you look at it. Then he uses a cartoon clip to explain how gravity holds us to the earth's surface.