# Physics

Notes on physics

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## Physics notes

• The speed of an object is a measure of how fast it is moving.

Speed (m/s) = Distance travelled (m) divided by Time taken (s)

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• The acceleration of an object is the rate at which its velocity changes. It is a measure of how quickly an object speeds up or slows down.

Acceleration (m/s2) = Change in velocity (m/s) divided by Time taken for change (s)

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• Kinetic energy - energy an object has because of its movement. It depends on the mass and speed of the object.

Kinetic energy (J) = 1/2 x Mass (kg) x Speed (m/s)2

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## Physics notes

• Forces are pushes or pulls. They are measured in newtons (N) and may - vary in size or - act in different directions.

Friction is a force that occurs when...

• an object moves through a medium, e.g. air of water.
• surfaces slide past each other.

Friction works against the object, in the opposite direction to which it is moving.

When a motor vehicle travels at a steady speed, the frictional forces balance the driving force.

The movement of an object depends on the forces acting on it.

• If the forces are equal and opposite then they are balanced, i.e. resultant force is zero.
• If the forces are not equal and opposite then they are unbalanced, i.ei resultant force not zero.
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