Year 10 physics summary

Topics: Energy, Heat, Thermodynamics Pages: 5 (1236 words) Published: March 16, 2014
Energy

Energy can neither be created or destroyed, only changed into different forms. Energy is only useful when it can be converted into different forms. Energy is often dissipated - spread out and lost.

9 types of energy:
Thermal (heat) - flows from hot to cold objects
Kinetic (movement) - anything that is moving has this
Light - from the sun, light bulbs et cetera
Elastically potential - when things are stretched
Gravitational potential - anything that can fall
Electrical - whenever a current flows
Sound - vibrations in the air
Chemical -a store of energy e.g. Batteries, food et cetera
Nuclear - released in nuclear reactions
E.g. A television gives out light, sound and heat.
Potential and chemical energy are all stores of energy because they are not actively doing anything but waiting to be changed into another type of energy.

To understand energy transfer, we must understand particles,

States of Matter
Substances can have different states of matter:
The state of matter that a substance is depends on the amount of energy that each of the particles has. Substances can change between states of matter:

As particles gain kinetic energy, they spread out more,
therefore becoming liquid and then gas. When
particles lose energy, they spread out less and
therefore become liquid and then solid.

Heat energy is energy on the move. Moving from places of high temperature to areas of low temperature. The bigger the temperature difference, the faster the heat transfer. Heat moves by three different processes:

Conduction - mainly in solids
Convection - mainly in liquids and gases
Radiation - any state of matter can absorb/emit infrared radiation.

Conduction
Vibrations in matter are passed on to transfer heat energy. This is called conduction. Insulator - a material that stops energy being transferred.
Solids are good conductors because the particles are closer together and so the particles collide more frequently. Good conductors have free electrons. Metals contain free electrons and so they are good conductors. Free electrons increase conductivity because they move faster and so collide with other particles more. Note: Good conductors often feel hotter/colder than the surroundings however this is not the case. Actually, the material is just conducting the heat into/away from your hand faster.

Infrared Radiation
All objects continually emit and absorb infrared radiation. It is emitted from the surface of an object. An object that is hotter than its surroundings will emit more radiation than it absorbs as it cools down and vice versa when an object is cooler than its surroundings. The hotter an object is, the more radiation it gives out in a given time.

Radiation and Surfaces
Good emitters and absorbers: Dark, Matt surfaces
Bad emitters and absorbers: light, shiny surfaces. These reflect infrared radiation.

Convection
Convection occurs mostly in liquids and gases when more energetic particles move from hotter regions to cooler regions and take their heat energy with them. Particles gain kinetic energy when they are heated, making the substance less dense. This makes the particles rise. Particles then lose energy in colder areas, causing the particles to become more dense and so sink. A steady flow of particles between warm and cold is called a convection current. Convection currents cause sea breezes in which air warmed by the land rises and is replaced by colder air from above the sea. Tip: always state the type of heat transfer involved.

Rate of Heat Transfer
Factors that affect heat transfer:
Surface area - the larger the surface area, the more IR radiation can be emitted or absorbed e.g. Radiators have a high surface area. Proportion of surface area to volume
Type of material - Good conductors will increase the rate of heat transfer. Temperature difference

Some products are designed to decrease the rate of heat transfer e.g. Flasks: Have double walls with a...
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