revision: Physics - Topic 4

4a) Units

4.1 - use the following units: kilogram (kg), joule (J), meter (m), meter/second (m/s), meter/second2 (m/s2), newton (N), seconds (s), watt (W)

kilogram (kg) - used for mass
joule (J) - used for energy
meter (m) - used for distance or height

meter/second (m/s) - used for speed or velocity
meter/second2 (m/s2) - used for acceleration

newton (N) - used for force or weight
second (s) - used for time
watt (W) - used for power

4b) Energy transfer

4.2 - describe the energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

These are all types of energy that you need to know of. :)

4.3 - understand that energy is conserved

Okay, so energy is conserved. This means that it cannot be created or destroyed. It can only be converted from one form to another. This is known as the law of conservation of energy! :D It's da law! 

Although, energy can be converted from one form to another, the total energy remains the same!~

4.4 - know and use the relationship: 
efficiency = Useful E_out / Total E_in

The amount of energy put in is always equal to the output. This is because it's da law! :D (see 4.3)

The efficiency is therefore the amount of energy from the energy input that is actually useful. Efficiency can be shown as a percentage.

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4.5 - describe a variety of everyday and scientific devices and situations explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams.

Sankey diagrams show the energy transfers that take place and how much energy is useful and wasted. They must show that energy is conserved so the total output is equal to the input. (Cuz it's da law!! :D)

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4.6 - describe how energy transfer may take place by conduction, convection and radiation.

Energy transfers in the form of heat in three possible ways - conduction, convection and radiation.

Thermal conduction is the heat energy transfer through a solid substance.
An increase in temperature results in an increase of kinetic energy allowing the particles within the solid to vibrate more - this is how energy is transferred from one particle to the next.

Thermal convection is the heat energy transfer through fluids (anything that flows, and can be poured - so liquids and gases.) moving upwards due to regions of the fluid that are less dense.
An increase in temperature results in the gas or liquid expanding, allowing the density to decrease closest to the source of heat. This results in the less dense fluid to float upwards.

Thermal radiation is the heat energy transfer in the form of infrared waves. (The only way heat can be transferred through a vacuum.

4.7 - explain the role of convection in everyday phenomena.

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4.8 - explain how insulation is used to reduce energy transfers from buildings and the human body.
 If you wear a lot of layers, you trap air and since air is an insulator - it will stop you from losing heat and keep you warm.

Curtains, carpets, glazed windows,