Sheldon dresses up as the Doppler Effect for Penny's Halloween party. When Penny asks about his costume, Sheldon explains the Doppler Effect to her.

Cole Trickle performs his first ride around the racetrack and finishes with an impressive time. As the car travels around the track, the sound of the motor changes in pitch.

Galileo explains to his student that, if two balls are dropped at the same height, they will both hit the ground at the same time, regardless of their weight.

Mr. Seaver begins teaching the class a lesson on gravity out of the textbook. He is especially confused by the book's claim that a coin and a feather will fall at exactly the same speed. After Luke challenges him to prove it, he tests the claim.

The students and Ms. Frizzle travel to Mercury, the first planet in our solar system, and learn that they weigh less because there is less gravity on the planet. They enjoy bouncing around with less gravity, and a few students take part in a contest to see who can jump higher.