Where energy is stored, the four ways it moves between stores, and how to calculate kinetic energy with E = ½mv².
What you will learn
- Name the energy stores and the ways energy is transferred
- Calculate kinetic energy
- Rearrange E = ½mv² to find a speed
Stores and transfers
Physicists keep track of energy by saying which store it is in.
The ones you need:
- kinetic: anything moving
- gravitational potential: anything raised up
- elastic potential: anything stretched or squashed
- thermal: anything warm (the hotter, the more)
- chemical: fuels, food (including the glucose a plant makes) and batteries
- also magnetic, electrostatic and nuclear
Energy moves between stores in four ways: mechanically (a force moves something), electrically (a current), by heating (hot to cold) and by radiation (light and infrared). Sound waves carry energy away too.
Heating and radiation are easy to mix up. Heating passes energy through matter that is touching: the particles of the hotter thing pass it on to the cooler thing next to them (conduction and convection). Radiation needs no contact: the infrared from a campfire crosses the air (or even empty space) to warm your face.
A system is just the object or group of objects you choose to look at. In a closed system, nothing gets in or out, and the total energy never changes. Energy cannot be created or destroyed: it is only moved from store to store.
"The energy is used up" is never right. When a car brakes, its kinetic energy goes into the thermal stores of the brakes and the air. It is still there, just spread out and no longer useful. Energy spread out to the surroundings like this is said to be dissipated.
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Stores and transfers
- Kinetic energy
- Going backwards: finding the speed
- Try it: Try it with the real tool
- Try it: Your first calculation
8 practice questions, marked as you go; about 20 minutes in all.
Key terms
Store, Mechanically, Electrically, By heating, By radiation, Heating, Radiation, System, Directly proportional, Significant figures
In this unit: Energy stores, transfers and efficiency
Energy stores and how energy moves between them, kinetic and potential energy, specific heat capacity, power, efficiency and the energy resources that make our electricity.
- Energy stores, transfers and kinetic energy
- Potential energy and energy conservation
- Specific heat capacity
- Power
- Efficiency, wasted energy and insulation
- Energy resources
- Required practical: thermal insulation