# Physics unit 1

My revision for what I need to know for my assessment.

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## Physics Unit 1 GCSE triple science Yr10

It all commences with Matter. States of Matter. All objects on this universe can be divided into 3 categories: Solids, Liquids & Gases.

• Solids:don't flow, have a fixed volume and shape and have a high density, vibrate with particles in a fixed position.
• Liquids:do flow, fit the shape of a container, have a fixed volume and a low density, move about at random but within the space/surface.
• Gases:do flow, can fill a containers shape but they don't have a fixed shape, their volumes can increase/decrease and their density is lower than liquid. They can move freely in ALL directions.
• all are made of molecules.

The density is the particle arrangement-how close are the particles???

Heat can travel in 3 methods:

1Conduction

2Convection

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## Heat transfer-Conduction

In metals: they are good heat conductors because of the free electrons they consist of. The electrons move around freely at random-not attracted by the nucleus-and hold the positive ions together. To transfer energy, these electrons collide among themselves with positive ions. In conclusion, the energy would have spread faster through the solid.

In non-metals:there are no free electrons. However, by the vibrating  particles, energy is transferred.The atoms vibrate faster and the bonds shake which passes the vibration on to the following atom. Overall, the temperature will have increased because of energy spreading through the solid.

Conduction occurs mainly in solids. Metals are the best conductors of heat energy, transferring it quicker than the heat energy in a non metal.

A good thermal insulator is a poor heat conductor. A poor thermal insulator is a good heat conductor.

A conductor transfers between solid substances.

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## Heat transfer-Convection

A convector transfers between liquid substances.this takes place in liquids and gases (fluids). When the heat energy is supplied, particles gain heat energy and become less dense, lighter and more energetic. The hot fluids particle has risen. The cold and more dense particles sink down, creating a convection current. This is how heat energy is transferred:

it always depends on the temperature.

Convection currents occur whenever the heating of fluids takes place. For example:

• Hot chocolate in a microwave
• Cake mixture in oven
• Oil in saucepan.

Convection can also occur in rooms from the heater. The heater warms the air closest to it, the heated particles rise, becoming less dense.

They bounce off the ceiling and circulate around the room, warming the air.

They finally fall downwards when the air has cooled and the particles drop becoming dense again. The cycle restarts.

Convection currents occur because the rising fluid loses heat which cools it.

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Heat energy can be transferred by radiation. It is a type of light wave.They can travel in vacuum which explains why we can feel the warmth of the sun-even though it is extremely distant.

Unlike convection, Heat radiation travels in ALL directions. Radiant heaters provide heat in bathrooms because of the electrical resistance that a hot bar holds which safely reflects heat. These travel in straight lines. All objects emit and absorb infra-red radiation however dark/black objects are good at absorbing/emitting the heat.

Light shiny surfaces are poor emitters of radiation so that the  liquid inside does not heat up/cool down swiftly which is why a flask has a shiny, light, silver surface. Thermal energy warmer-->cooler regions. Radiation transfers between ALL substances.

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## Kinetic energy

Kinetic energy involves the energy's transfer from hot to cool regions because of the temperature differences in between them.

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## Rates of Heat transfer

• Temperature difference: heat transfers from a hot  region to a cooler region. this transfer will continue if there is a temp. difference (conduction)
• Material: The second variable depends on the material that transfers the heat.
• (Surface) area: The area through which heat is being transferred-i.e-larger the window, larger the amount of heat loss.Conclusively, an object with a wider area has its surface particles conducting heat.
• Thickness/distance:The thicker the insulation, the lower the heat transfer rate-no escape of heat-i.e-wearing thick layers in cold climate-->good insulation, body heat/air trapped.
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