Science · 7th Grade · Energy and Matter in Motion · Weeks 1-9

Conservation of Energy

Students analyze systems to demonstrate that energy is conserved, transforming between kinetic and potential forms without loss.

• Common Core State Standards
• MS-PS3-2

About This Topic

Conservation of energy is one of the most important principles in all of physics: energy cannot be created or destroyed, only transferred or transformed. This topic addresses MS-PS3-2, asking students to construct, use, and present arguments to support the claim that energy, when it transforms, is always conserved. Students observe this in systems like pendulums and roller coasters, where energy continuously shifts between kinetic and potential forms.

In the US K-12 context, this standard asks students to use evidence and reasoning rather than simply stating the law. Students should be able to identify where energy is at different points in a system, track transformations, and explain why a real system loses usable energy to heat and sound without violating conservation. This understanding is foundational for all future work in thermodynamics, mechanics, and environmental science.

Tracking invisible transformations is challenging without concrete anchors. Active learning gives students the tools to trace energy through real systems, argue from data, and challenge the common belief that energy disappears when something slows down.

Key Questions

1. Analyze how energy transforms between kinetic and potential forms in a pendulum.
2. Justify the statement that energy cannot be created or destroyed.
3. Predict the final speed of an object given its initial potential energy.

Learning Objectives

• Analyze the transformation of energy between kinetic and potential forms in a simple pendulum system.
• Construct an argument, using evidence from observations, that energy is conserved and cannot be created or destroyed.
• Predict the final speed of an object based on its initial potential energy and the system's efficiency.
• Explain how energy is transferred and transformed within a closed system, such as a roller coaster.
• Evaluate the impact of friction and air resistance on energy transformations in real-world mechanical systems.

Before You Start

Introduction to Energy Forms

Why: Students need a basic understanding of different types of energy, including kinetic and potential, before analyzing their transformations.

Forces and Motion

Why: Understanding concepts like velocity, acceleration, and gravity is essential for analyzing how energy changes with movement and position.

Key Vocabulary

Potential Energy	Stored energy an object possesses due to its position or state. For example, a ball held high has more potential energy than when it is on the ground.
Kinetic Energy	The energy an object has due to its motion. A moving car possesses kinetic energy, which increases with its speed.
Energy Transformation	The process where energy changes from one form to another, such as when potential energy is converted into kinetic energy as an object falls.
Conservation of Energy	A fundamental principle stating that energy cannot be created or destroyed, only changed from one form to another or transferred between systems.
System	A collection of interacting or interdependent components forming a unified whole. In physics, a system can be a pendulum, a roller coaster, or even the Earth.

Watch Out for These Misconceptions

Common Misconception

Energy is destroyed when an object stops moving.

What to Teach Instead

When something stops, its kinetic energy has transferred to thermal energy in the surroundings, not vanished. Measuring the slight temperature increase of a surface after a ball bounces repeatedly helps students see where the energy went.

Common Misconception

Conservation of energy means no energy is ever lost from a system.

What to Teach Instead

Conservation means the total amount in the universe is constant, not that a specific system retains all its energy. Students often confuse the law with 'no energy loss' until they track where energy exits a system as heat or sound.

Active Learning Ideas

Inquiry Circle: The Pendulum Tracker

Groups use a simple pendulum and a tape measure to record the height at the start of each swing. They graph how starting height relates to speed at the bottom and track how long the pendulum takes to stop, then use the data to argue that energy transferred to the surroundings rather than vanished.

45 min·Small Groups

Think-Pair-Share: Roller Coaster Energy Analysis

Show a diagram or simulation of a roller coaster with labeled heights. Students individually identify where kinetic energy and potential energy peak, then explain to a partner why the coaster cannot return to a height higher than its starting point. The class compiles their reasoning into a shared argument.

20 min·Pairs

Stations Rotation: Energy Transformation Tracking

Three stations each model a different system: a wind-up car, a bouncing ball, and a hand-crank generator. At each stop, students diagram the full energy transformation chain and identify where energy exits the system as heat or sound.

50 min·Small Groups

Gallery Walk: Energy in Everyday Systems

Student groups create annotated posters showing a chosen system (e.g., a swing, a thrown ball, a charging phone) with arrows mapping each energy transformation. Peers use sticky notes to identify which transformations were correctly shown and ask questions about missing steps.

35 min·Small Groups

Real-World Connections

• Mechanical engineers design roller coasters, like those at Six Flags parks, by calculating energy transformations to ensure safe speeds and thrilling rides, accounting for friction and air resistance.
• Athletes in sports such as pole vaulting or gymnastics rely on the principle of energy conservation. They convert their running kinetic energy into potential energy at the peak of their jump or flip, then back into kinetic energy.
• Renewable energy technicians install wind turbines, which transform the kinetic energy of wind into electrical energy, demonstrating energy transfer and transformation on a large scale.

Assessment Ideas

Exit Ticket

Provide students with a diagram of a pendulum at its highest point and lowest point. Ask them to: 1. Label where potential energy is greatest. 2. Label where kinetic energy is greatest. 3. Write one sentence explaining how energy transforms between these two points.

Quick Check

Present a scenario: 'A toy car starts at the top of a ramp with 100 Joules of potential energy. It rolls down and reaches the bottom with 80 Joules of kinetic energy. Where did the other 20 Joules of energy go?' Ask students to write their answer and justify it using vocabulary terms.

Discussion Prompt

Pose the question: 'If energy cannot be destroyed, why does a bouncing ball eventually stop bouncing?' Facilitate a class discussion where students use terms like kinetic energy, potential energy, transformation, and friction to explain the energy losses to heat and sound.

Frequently Asked Questions

What does conservation of energy mean in science?

Conservation of energy means that the total amount of energy in a closed system stays constant. Energy can change forms, such as from potential to kinetic to thermal, but the total never increases or decreases.

How can active learning help students understand energy conservation?

Energy conservation is easiest to understand when students track it through real systems. Using pendulums, bouncing balls, or roller coaster simulations, students collect data showing energy shifting forms rather than disappearing. This evidence-based approach directly supports the MS-PS3-2 standard's emphasis on constructing arguments from data.

Why doesn't a pendulum swing forever if energy is conserved?

Energy is conserved, but that does not mean it stays in the pendulum. The pendulum gradually transfers its energy to the surrounding air through air resistance and to heat at the pivot. The system loses organized motion, but the total energy in the universe remains the same.

How do potential and kinetic energy trade off in a swinging pendulum?

At the highest point of the swing, the pendulum has maximum potential energy and zero kinetic energy. At the lowest point, it has maximum kinetic energy and minimum potential energy. The energy shifts smoothly between forms with each swing.