Energy Exchange Slides Energy
Exchange
The Physics of Conservation
Phase 01
WARM-UP
The Tennis Ball Test
If I drop a tennis ball, why does it bounce back up?
Does it reach the exact same height as where I dropped it?
Why or why not? Discuss with your neighbor.
Essential Question
What transformations occur when
a ball is raised and released?
Video Analysis
Duration: 1:13
Embedded media
Key Observation
Watch the GPE and Kinetic bars. How do they behave relative to each other?
The "Spike"
Pay close attention at 0:44. What is the third energy type that appears?
The Big Three
GPE
Gravitational Potential Energy
Energy stored due to an object's height above the ground.
Kinetic
Energy of Motion
Energy an object has because it is moving.
Elastic
Elastic Potential Energy
Energy stored when an object is compressed or stretched.
Ideal Models vs.
Real World
1
The video shows an ideal system where no energy escapes.
2
In reality, energy transfers out of the system in ways we can hear and feel.
3
Energy isn't "lost"—it just moves to the environment as sound and thermal energy (heat).
THE
Where does it go?
Sound Waves
Vibrations from impact
Friction & Heat
Air resistance + internal friction
Phase 02: Main Activity
The Missing
Energy
Observe
Watch your Newton's Cradle for 2 minutes. Notice what happens to the height of the balls over time.
Diagram
Draw the system. Label where energy is transferring OUT of the system as sound or heat.
Final Thought
"Energy is neither created nor destroyed..."
...it only changes form or location.
Conservation of Energy
Energy Detective Worksheet Energy Detective
System Analysis: Newton's Cradle
Name
Date
Mission Objective
Identify evidence of energy conservation and transformation within a real-world mechanical system. Track the "missing" energy that an ideal model doesn't account for.
Part 01
System Mapping
Watch your cradle for 2 minutes. In the space below, draw a detailed diagram of the Newton's Cradle. Use arrows to show where energy is transferring out of the system (think: sound and heat).
Draw Diagram Here
Look for evidence of:
Sound Waves • Air Friction • Surface Heat
Part 02
Energy Audit
Evidence of Sound Energy:
Evidence of Thermal Energy (Heat):
Part 03
The Reality Gap
In the video we watched, the energy bars (GPE, Kinetic, Elastic) perfectly balanced. However, in your experiment, the balls eventually stop. Why is the video's graph an "ideal" model while your cradle is a "real-world" observation ? Explain using the concept of energy transfer.
"Energy is never lost, it just becomes less useful."
Cradle Quest Discussion Cards Card 01
The High Point
Watch the ball at the peak of its swing. Why is the Kinetic energy bar at zero right now?
Video timestamp: 0:29
Card 02
The Fast Point
At the very bottom of the arc, where did all the Potential Energy go? What did it transform into?
Video timestamp: 0:36
Card 03
The Impact
Why is there a third bar called "Elastic" ? What is physically happening to the metal balls at this exact micro-second?
Video timestamp: 0:44
Card 04
The Sound
If energy cannot be destroyed, where does it go when the cradle eventually stops swinging? Name two places it transfers.
Main Activity Discussion
Card 05
The Prediction
Compare a tennis ball to a bowling ball. If dropped from the same height, which one has more GPE ? Why?
Extension Discussion
Card 06
The Big Picture
How does a Newton's Cradle prove the Law of Conservation of Energy ?
Closure Discussion
Energy Exchange Teacher Guide Energy Exchange
Teacher Facilitation Guide
Grade Level
7th Grade
Subject
Physical Science
Instructional Objective
Students will identify and explain evidence of energy conservation and transformation within a mechanical system (Newton's Cradle). They will differentiate between "ideal" models and "real-world" energy transfers (sound, friction, thermal).
Pacing & Flow
05m
Warm-up: The Tennis Ball Drop
Key question: Why doesn't it return to the original height? (Energy transfer to floor/air).
10m
Video Analysis & Discussion
Watch for the "Elastic" energy spike at 0:44. Use Discussion Cards for group check-ins.
20m
Main Activity: The Missing Energy
Groups observe physical cradles and map the "leaks" (sound, friction) on worksheets.
10m
Closure: Share-out & Final Thought
Reinforce: Energy isn't lost, just transformed into less "useful" forms.
Materials List
Newton's Cradles (1 per group)
Tennis Balls (for warm-up)
Energy Detective Worksheets
Discussion Cards (set of 6)
Stopwatches / Timers
Vocabulary
GPE: Potential energy due to height.
Kinetic: Energy of motion.
Elastic: Energy stored in compression.
Ideal System: A model where no energy is lost.
Facilitation Secrets
Common Misconceptions
"The energy just disappears."
Students often think the cradle stops because energy is used up. Remind them it's transferred to air molecules (friction) and sound waves. Energy never vanishes.
"The balls are perfectly hard."
The "Elastic" spike at 0:44 is vital. Explain that steel compresses like a very stiff spring. Without this compression, energy wouldn't transfer through the middle balls.
Worksheet Answer Key
Part 01: Diagram Labels
Sound waves radiating from the point of impact.
Air resistance arrows pushing against the balls.
Heat at the strings/pivot point and impact site.
Part 03: Ideal vs. Real
"The video is an ideal model because it assumes no energy is transferred to the environment. In the real world, the clicking sound and friction with the air transfer energy away from the spheres, causing them to lose height until they stop."
