Energy
ICSE Class 7 · Physics · Chapter 3
What this chapter covers
- Energy as the capacity to do work
- Units of energy: the joule and the calorie
- Different forms of energy
- Mechanical energy: kinetic and potential
- Interconversion of energy
- The law of conservation of energy
- Real-world examples of conservation of energy
Key definitions
Energy is the capacity of a body to do work.
Work is said to be done when a force acts on an object and the object moves because of that force.
The joule is the SI unit of energy and of work.
The calorie is an older unit of energy, used mainly for heat energy.
Kinetic energy is the energy a body has because it is moving.
Potential energy is the energy a body has because of its position or its shape.
Heat energy is the energy that flows from a hotter body to a colder body and makes things warmer.
Electrical energy is the energy carried by an electric current flowing through wires.
Light energy is the energy that lets you see the things around you.
Sound energy is the energy carried by vibrations that travel to your ears.
Chemical energy is the energy stored in substances such as food, fuels and the materials inside a battery.
Mechanical energy is the total of the kinetic energy and the potential energy of a body.
Key points
- Energy is the capacity of a body to do work.
- Work is done when a force moves an object; doing work uses energy, and work done on a body gives it energy.
- The SI unit of energy and work is the joule (J); 1 kJ = 1000 J.
- One calorie is the heat needed to raise the temperature of 1 g of water by 1 °C; 1 cal is about 4.2 J; 1 kcal = 1000 cal.
- The main forms of energy are kinetic, potential, heat, electrical, light, sound and chemical energy.
- Kinetic energy is due to motion and is greater for a heavier or faster body.
- Potential energy is due to position or shape and is greater for a higher or heavier body, or for a more stretched or wound spring.
- Mechanical energy is the total of kinetic and potential energy.
- Interconversion of energy is the change of energy from one form into another; energy conversion diagrams show these changes with arrows.
- The law of conservation of energy: energy can neither be created nor destroyed, only changed from one form into another.
- A pendulum, a roller coaster and a hydroelectric power station all show potential and kinetic energy changing into each other, with some energy turning into heat and sound.