Beakman smashes a tomato with a mallet. Then puts another tomato in liquid nitrogen to show it was frozen and hits with a mallet. He then takes a blown up balloon and puts it in a bowl. He pours liquid nitrogen over it and shows the balloon shrinking. He explains this happens because everything is made of molecules. Then he uses a cartoon schematic to explain further. He also shows that when the balloon gets warmer, the air starts to expand and fills back up the balloon.
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.