# Key Physics Topics

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• Created by: xerinx
• Created on: 10-03-19 13:53

## Newton's First Law

• A resultant force is needed to make something start moving, speed up or slow down
• If the resultant force on a stationary object is zero, the object will remain stationary
• If the resultant force on a moving object is zero, it will carry on moving at the same velocity
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## Newton's Second Law

• Acceleration is proportional to the resultant force
• The larger the resultant force acting on an object, the more it accelerates
• Acceleration is inversely proportional to the mass of an object
• Therefore, an object with a larger mass will accelerate less than one with a smaller mass
• The formula for the second law is:

F = m x a

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## Momentum

p = m x v

momentum(kg m/s) = mass(kg) x velocity(m/s)

• The greater the mass or velocity of an object, the more momentum the object has
• Momentum is a vector as it has a size and direction
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## Changes in Momentum

• A force causes momentum of an object to change
• A resulatant force of an object causes it to accelerate ( Newton's 2nd Law)
• Acceleration is a change in velocity over time, so:

force = mass x change in velocity / time

• This means a force applied to an object will change its velocity
• Mass x change in velocity is equal to change in momentum, so:

force = change in momentum / time

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## Energy Stores

The types of energy stores are:

• Kinetic
• Thermal
• Chemical
• Gravitational Potential
• Elastic Potential
• Electrostatic
• Magnetic
• Nuclear
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## Kinetic Energy

When an object is moving, it has energy in its kinetic energy store

You can find the energy in a kinetic energy store using:

kinetic energy = 0.5 x mass x ( speed x 2 )

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## Conservation of Energy

Energy is never created or destroyed

Energy can be stored, transferred between stores, and dissipated - but it can never be created or destroyed.

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## Efficiency

• Usefull devices can transfer energy from one store to a usefull store
• However, some of the input energy can dissipate into the surroundings

You can calculate the efficiency of any device using:

efficiency = useful energy / total energy supplied

This gives you a decimal so to find a percentage you need to multiply the answer by 100

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## Energy Resources - Renewable

• Renewable resources will never run out as they can be renewed as it is used
• Most of them do damage to the enviroment but not as much as non-renewable resources

They include:

• Bio-fuels
• Wind
• The Sun (solar)
• Hydro-electricity
• Tides
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## Energy Resources - Non-Renewable

• Non-renewable energy resources are fossil fuels and nuclear fuel
• They provide the most of the worlds energy
• They are natural resources that form underground over trilions of years
• The main fossil fuels are oil, coal and gas
• They emmit carbon dioxide into the atmosphere when they're burned, which adds to the greenhouse effect, and contributes to global warming
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