# Physics - Forces and Energy

This set of cards is for IGCSE Physics and specifically for Forces and Energy and has seven subtopics which are:

Work and Energy          Energy Transformation         Calculating PE and KE         Efficiency and Power          Energy for Electricity

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## Work and Energy

Work done is measured in Joules (J) and the equation for it is:

work done (J) = force (N) x distance (m) or W = F x d

Work done is the amount of energy put into something.

There are many different kinds of energy which are:

Kinetic (movement)

Gravitational Potential (An object held up which would fall by gravity)

Elastic Potential (A stretched object)

Chemical Potential (fuels like petrol and food)

Electrical Potential (The flow of electrons)

Nuclear Potential (forces in atoms)       Thermal (Heat)        Radiated (waves)

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## Energy Transformation

Energy is neither created nor destroyed but only transformed.

For example, when a pebble is thrown up in the air, chemical energy from the thrower is transformed to kinetic energy as the stone flies up, when the stone stops for a milisecond at its highest point it has gravitational potential energy, this transformed to kinetic energy as it falls and as it hits the ground there is sound (radiated) energy.

This is all known as the law of conservation.

We can,, however, waste energy. For example, if you have a light it uses chemical energy from the batteries, the useful energy is the light (radiated) energy however energy is also wasted through the thermal energy used as well.

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## Calculating GPE and KE

GPE (gravitational potential energy) can be calculated by this equation:

gravitational potential energy (J) = mass (kg) x gravity (N/kg) x height (m)

or GPE = m x g x h

KE (Kinetic energy) can be calculated using this equation:

kinetic energy (J) = 1/2 x mass (kg) x velocity ² (m/s)

or KE = 1/2 x m x v ²

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## Efficiency and Power

As said before, some energy can be wasted. The efficiency of a subject can be found using:

efficiency (%) = useful work done (J) / total energy input (J)

Power (measured in watts) is the rate at which something is done. Power can be worked out using:

power (W) = work done (J) or energy transformed (J) / time tkaen

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## Energy for Electricity

There are many different forms of generators that turn energy into electricity which are all renewable, such as:

Hydroelectric damn produces no pollution, no fuel cost and lots of power generated. HOWEVER: Sediment build up blocks the damn, and the reservoir destroy wildlife and dislocates people.

Solar Energy is light free, no pollution or moving parts. HOWEVER: The sun does not always shine, not much electricity produced, expensive and inefficient.

Tide Power has no fuel cost, no pollution, lots of energy produced and very predictable. HOWEVER: They are expensive and environmentally destructive.

Wave Power has no fuel cost, no pollution and not expensive. HOWEVER: they are easily damaged through corrosion, difficult to maintain and unpredictable.

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