Grade 7 · Energy Transfers · Energy Stores and Transfers
Energy Stores and Transfers
Where energy is stored, how it moves, and why it is never lost.
Learning objectives
- Name the main energy stores.
- Describe transfers using pathways.
- Apply conservation of energy to a system.
NGSS alignment
MS-PS3-5
Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object.
HS-PS3-1
Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other components and energy flows in and out of the system are known.
MS-PS3-1
Construct and interpret graphical displays of data to describe the relationships of kinetic energy to the mass of an object and to the speed of an object.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion D — Reflecting on the Impacts of Science
ENGAGE
A cold phone battery
After 20 minutes of gaming, a phone battery is nearly empty and the phone is warm to touch.
Think about it
- Where did the energy in the battery end up?
- Was any energy destroyed?
EXPLAIN
Stores, pathways and efficiency
| Store | Example |
|---|---|
| Kinetic | A moving ball |
| Gravitational potential | A book on a high shelf |
| Chemical | Food, fuel, a battery |
| Elastic potential | A stretched spring |
| Thermal | A hot drink |
| Nuclear | Uranium fuel |
Pathways
- Mechanically, by a force moving an object
- Electrically, by a current in a circuit
- By heating, from hot to cold
- By radiation, such as light or sound
Conservation of energy
Energy is never created or destroyed. It is transferred between stores, and some always ends up dissipated to the surroundings as thermal energy.
Efficiency = useful energy transferred / total energy supplied. A device is never 100 percent efficient because some energy is always dissipated.
Watch
Work, Energy and Power: Crash Course Physics
CrashCourse · 10 min
Shows how energy moves between stores.
Before you watch: Can energy be destroyed?
- Name three energy stores.
- Why is no device 100 percent efficient?
Interactive simulation · PhET
Energy Forms and Changes
Switch on the energy symbols and follow the energy from the source to the light bulb.
While you explore
- Where does some of the energy end up that you did not want?
- Is any energy destroyed anywhere in the chain?
Key vocabulary
- Dissipation
- Energy spreading out and becoming less useful.
- Energy store
- Where energy is held before it moves.
Practice questions
0/2 correct
Level 1 · Criterion A
A stretched catapult stores energy mainly as:
Level 2 · Criterion A
A motor supplies 500 J and does 400 J of useful work. Its efficiency is:
MYP criterion tasks
Level 3 · Criterion D
A student says the energy in a phone battery is used up. Rewrite this statement so that it is scientifically correct.
Reflect & track
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