Sample Lesson: "Water Bottle Rockets"

Observations and Experiments

In order to understand a scientific concept, students need to observe it in action. If they merely memorize concepts without the foundation of experience and observation, they won’t be able to apply those concepts in real life situations.

Every Rock-it Science lesson provides individual as well as group activities that give students the opportunity to make observations. As students collect observations throughout life, their natural intelligence converts them into the generalities we call “concepts.”

Here’s an example of how we introduce students to Newton’s laws of motion through a lesson called “Water Bottle Rockets.” The Objective: Students will discover ways to make their water bottle rockets fly higher and farther.

Part 1: Introduction
If a person is floating in space and she happens to see a bowling ball heading right at her, she has a problem!

Without something to push against, she can’t move out of the way! She can wildly swing her arms and legs, but she’s going nowhere. This is one of those laws that we just can’t escape: “If a body is at rest, it will remain at rest unless acted upon by a force.”

We call this inertia, and it only depends on how heavy (massive) something is, because the heavier it is the harder it is to move.
If our person had a bowling ball in her back pocket, then she could do one of at least two things: one, she could throw it right at the oncoming bowling ball to knock it out of the way. Or two, she could throw her bowling ball as hard as possible in any other direction!
Sir Isaac Newton figured this out with math:
Force equals mass times acceleration (f = ma).

We know that a force is a push or a pull, mass is like weight (at least on earth), and acceleration is when something speeds up.
So when she throws the bowling ball, she is applying a force to it, so it speeds up and flies away.

But how could this possibly save her?

Newton said this, too: “For every action, there is an equal and opposite reaction.”
This means that the force that you used to throw the bowling ball would also be acting against her hands, so her hands would be pushed in the opposite direction. Now, if her hands happened to be attached to her arms, and if her arms were attached to her body & her whole body would accelerate opposite the direction that she threw the bowling ball. If you were her, a good plan would be to throw your bowling ball straight up and this would make you go down out of the way of the one that was going to hit you.

During an event at NASA, a water bottle rocket disappears a moment after launch, leaving a trail of water behind.

So even floating in space it’s possible to move yourself out of harm’s way.

I like to remember the 3 earthly laws of motion by Isaac Newton as:

Objects are lazy; they stay where you put them.

They’ll move, but you have to push them.

As you push on them, they’ll push back just as hard!

In our experiment today we are going to try to make something accelerate by throwing some air molecules out the window or by throwing out a thousand times more water molecules.

By the way, some air molecules means about:
10,000,000,000,000,000,000,000 (ten thousand million million million air molecules)

But first we need a fractured fairytale . . .
Continue to Part 2, The Story