1. ENERGY
UNIT 4

2. Forms of energy
Light energy : mostly comes from the sun. We can use torches and candles.
Thermal energy: provides from the sun and fossil fuels (coal, oil, gas…)
Electrical energy: is produced by burning fossil fuel, sunlight, wind and water.
Sound energy: is made by vibrations.
Chemical energy: is released when there is a chemical reaction. ( wax and oxygen)
Kinetic energy: when an object moves, it has kinetic energy.

3. Thermal energy When we heat a substance, we add thermal energy.
Temperature is the measurement of how hot or cold something is.
It isn’t the same as heat.
For measuring temperature the mains scale is Celsius scale.
Natural: sun wood, fossil fuels.
Man-made: heaters, radiators, toasters, irons…
sources
When we add thermal energy to a substance can happen:
The temperature of the substance increases.
The substance can change state.
When a substance gets warmer, the energy of the particles increases and this means the particles move faster and further apart.
Heat insulators don’t transfer heat very effectively. (wool, wood and plastic)
Heat conductors can transfer heat quickly and effectively. (iron, cooper and aluminium)
Conduction is one way that heat is transferred.
It occurs between two objects that are in contact.
The faster moving particles in the warm object collide with the slower moving particles in the cooler object and transfer some of their energy to these slower moving particles.
A change in the thermal energy of a substance can make the substance change state.
Melting: if the thermal energy in a solid increases, it may become liquid.
Evaporation: If the thermal energy in a liquid increases, it may become a gas.
If the thermal energy of a gas increases, it can make the gas expand.

4. LIGHT ENERGY Light sources produce light. They can be:
Natural: the sun stars, lightning.
Man-made: light bulb, torch, candles, fire, electrical equipment (TV)
Light travels in all directions and always in straight lines.
It can travel at up 300,000km per second. It’s the fastest form of energy.
When light meets an opaque object, the object blocks the light and a shadow forms on the opposite side of the object.
The light is made up of different colours. We can see seven colours in a rainbow or a spectrum.
Light energy allows us to see.
Light can’t pass through opaque materials (metal). These reflect or absorb the light.
Light passes through translucent materials (cellophane) but these disperse the rays of light.
Light passes through transparent materials (glass).
When light hits an opaque object at one angle it is reflected at the same angle.
Reflection is when light hits an opaque material and changes direction.
Refraction is when light passes through one transparent material to another with a different density and bends where the two surfaces meet.
Lenses are transparent objects which we use to change the direction of light by refraction.
Convex focus the rays of light together.
Concave disperse the rays of light.

5. Sound energy Vibrating objects produce sound.
Sound travels in waves. In all directions.
Sound can travel through the air, liquids and even solids, even they are opaque. It can produce changes in other things.
Sound can’t travel through a vacuum.
Sound can be reflected. The reflected sound can produce an echo.
loud sounds
Intensity: how much energy a sound can transfer.
Distance affects it. quiet sounds
Pitch: the number of vibrations a second that the source generates.
Tone: identify the source that is producing the sound.
CHARACTERISTICS