Unit #1

Activity Overview

Rubber balls have properties, like elasticity ["bounciness"] and kinetic energy [energy of motion] which can be converted into other forms of energy.

Students discuss varying forms of energy and how one form can be converted into another.
They then experiment with superballs to observe their behavior by dropping them and rolling them toward other objects to see how much they can push another object before coming to rest. Observations of varying elasticity [“bounciness”] and kinetic energy [energy of motion] due to differences in velocity [speed] and mass are be made.

Learning Objectives

• Determine when something has kinetic energy.
• Name at least one type of energy into which the kinetic energy of a superball can be converted.
• Describe what happens to the kinetic energy of a superball as it bounces lower and lower.

Conceptual Prologue

Macro-Micro Connection

It is the behavior of atoms that explains why the hot air balloon inflates when it is heated and why it rises when the air gets hot enough. In order to truly understand why a hot air balloon flies students need to understand how atoms behave. By studying bouncing balls, students will get an idea of the basic behavior of atoms.

Science Concepts

Superballs are used in this activity because, like atoms and molecules, they have the property of elasticity ["bounciness"], and when in motion, possess a certain amount of kinetic energy [energy of motion]. The amount of energy they have depends on their mass and velocity [speed]. An object with more mass and/or higher velocity [speed] will have more kinetic energy [energy of motion].

For example, if a bowling ball and a tennis ball are moving at the same velocity [speed], then the bowling ball has more kinetic energy because it has more mass. If the bowling ball and tennis ball are to have the same kinetic energy [energy of motion], then the tennis ball would have to be moving much faster than the bowling ball. A rough estimate of the comparative kinetic energy [energy of motion] possessed by an object, can be gauged by how hard it would be to stop that object from moving.

When most objects bounce off something, they convert some of their kinetic energy [energy of motion] into heat or sound energy. That is why, when you drop a superball straight down, it bounces to lower and lower heights each time. Its kinetic energy [energy of motion] is changing to heat and sound energy.

Naive Conceptions

• Kinetic energy is only related to velocity.

Kinetic energy is related to both mass and velocity. Often students forget about the mass component of kinetic energy.

• Energy is not conserved.

Energy is conserved. When a superball bounces to a lower and lower height, students often think that it is losing energy. In fact, some of its kinetic energy is converted to other forms, such as heat and sound. The air around the moving ball is warmed as the ball moves through it, the ball and floor are warmed during each impact, and sound is emitted during impacts.*

*Sound is also emitted as the ball moves through the air, but usually at a level too soft to hear.

Activity Design and Execution

Major Science Concepts:	• Kinetic energy • Conservation of Energy
Assumed Previous Knowledge:	• None
Time:	• Approximately 30 minutes
Materials:	For each group: • Bouncy balls of various masses • Some cans, bottles, (or other objects for the balls to roll into) • Computer with Workbench software
Advanced Preparation: (if any)	• None

Investigative Question: What is kinetic energy and how does it relate to the motion of superballs?

1. Explain to students that in order to understand what is happening to the hot air balloon, that it is not enough to just know that the balloon and the air inside made of atoms. Tell them they need to know how those atoms behave and that because atoms are too small to handle individually they will use bouncy balls to explore some simple behaviors of atoms. Balls behave very much like atoms.
2. Ask students to brainstorm different kinds of energy that they know about and list these on the board. Have the copy these into their notebooks.
3. Explain that the energy of motion is called kinetic energy and that one kind of energy can be converted to another [such as heat or light] but that it is never created or destroyed.
4. Drop a ball in front of the class and let it bounce for a while.
5. Ask the students why the ball stops bouncing. Ask for ideas and get into a discussion of where the energy goes (see info in conceptual prologue - science concepts).
6. Hand out the Kinetic Energy Lab and have them answer the questions.

Assessment

Have students write several things in their notebooks:

1. Explain in your own words what kinetic energy is.
2. You observe three things: a person sitting in a chair, and a dog chasing a car, moving at the same speed as a car. Which of those things have kinetic energy? Which has the most kinetic energy and why?
3. When you put on the brakes to slow down a car, where does all the kinetic energy go? What do you think happens to the temperature of the brakes?
4. When the burner of the balloon is turned on a lot of heat energy is released. Where does this energy go? How do you think it affects the kinetic energy of the air inside the balloon?