Unit F: Energy and Motion

How do roller coaster cars keep moving without the motor?

1. Get Set to Explore

Vocabulary

• kinetic energy: Energy an object has due to its motion.
• potential energy: Stored energy due to an object's position or due to its chemical composition.

Building Background

• Review the vocabulary words and definitions with the class. Make sure that students understand the difference between kinetic energy and potential energy. Review the idea that potential energy can change to kinetic energy and back again.
• Let volunteers share their experiences riding on roller coasters. Draw one or more rises for a roller coaster and ask students when they think the roller coaster cars would have the most potential energy and when they think they would have the most kinetic energy. Have them refer to your drawing, labeling it, as they explain. Keep the drawing up on the board to refer to later.
• Remind students that with most roller coasters, the ride starts at a low point, near the ground. Explain that a roller coaster has to overcome gravity to get to the top of the first hill it goes up. Let students speculate on how the roller coaster gets to the top of that first hill. If necessary, explain that a motor pulls the roller coaster to the top of the first hill.
• Present the Discover! question: On some roller coasters, a motor pulls the cars up the first hill. After that, the cars stay in motion without the help of the motor. How do the cars keep moving without the motor? Refer students to the drawing on the board and record their answers.

2. Guide the Exploration

• Direct students to launch the Discover! Simulation. Explain that in the first part of the simulation, students will watch a roller coaster ride. Call students' attention to the energy bars that appear below different parts of the roller coaster. Tell students that these bars give a big hint for answering the Discover! question.
• After students have watched the demonstration and listened to the narration, they should play the game. The game allows students to design their own course and see if the roller coaster can make it to the end of the course.
• After students have spent some time playing the game, return to the Discover! question and to the drawing on the board. Let students share their new insights.

3. Review/Assess

• Let a volunteer read the first three sentences of Step 3's Wrap-Up text. Ask the class to identify the invisible change. Guide students to understand that the roller coaster cars are gaining potential energy as they travel to the top of the first hill. Have another volunteer read the next three sentences. Let students describe the pattern of energy changes, relating their ideas to the roller coaster ride.
• Read the last three sentences of the Wrap-Up text to the class. Make sure students understand that the height of the first hill is the key to the roller coaster's ability to run the rest of the course without a motor.
• Challenge students to try the Extension activity. Guide students to realize that if the first hill is lower than subsequent hills, the roller coaster cars won't have enough potential energy to reach the top of the higher hills. The roller coaster will climb as far as it can and then stop and roll backwards down the track. It will be stuck going back and forth between the low hill at the start of the course and the higher hill in the middle of the course. The back-and-forth motion will continue until the kinetic energy is used up due to friction.

If time permits, present children with the following questions and activity:

• Critical Thinking Draw Conclusions Friction eventually slows roller coaster cars so that they come to a complete stop. What are two types of friction that affect a roller coaster? Which do you think affects the roller coaster ride the most? How do riders on the roller coaster often increase the other kind of friction? Answer: Friction between the wheels and the track and friction between the air and the cars. The former affects the roller coaster ride the most. Riders on the roller coaster often increase air resistance by raising their arms during the ride.

4. Reaching All Learners

English Language Learners

Pair native English speakers with English Language Learners to have them talk about experiences with roller coasters. You may wish to provide children with a video they can watch or a small chalkboard or dry-erase board they can use to talk about what it is like to ride on a roller coaster. Post the vocabulary students should use in their discussion. These words should include roller coaster, roller coaster cars, hills, loop, and gravity. Give English Language Learners the opportunity to learn this basic vocabulary before reviewing and reinforcing the science vocabulary with the class.