# Physics AS Mechanics Unit 2

Set of revision cards containing definitions and equations included in specification.

## Moment

Force x perpendicular distance

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## A Vector is...

...A physical quantity with both magnitude and direction

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## A Scalar is...

...A physical quantity with magnitude only

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## Velocity

Change in distance / Change in time

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## Acceleration

Change in velocity / Change in time

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## Equations of Motion

v = u + at

2s = (u+v) x t

v^2 = u^2 + 2as

s = ut + 0.5 x a x t^2

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## Force

Mass x Acceleration

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## Work Done (Energy Transferred)

Force x distance moved

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0.5 x m x v^2

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## Gravitational Potential Energy (GPE)

m x g x (change in h)

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0.5 x k x e^2

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## Work done to overcome friction

mgh - 0.5 x m x v^2

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## Power

The rate of transfer of energy

Measured in Watts.

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## Equations of Power

Energy transferred / time

Work done / time

Force x Velocity

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## The efficiency of a machine..

useful energy transferred by the machine / total energy supplied into the machine

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## Principle of Conservation of Energy

Energy cannot be destroyed or created, it can only be turned into different forms.

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## Joules (J)

Energy is measured in Joules.

One Joule is defined as the energy required to move an object of weight 1N through a distance of 1m.

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## Watt (W)

Power is measured in Watts.

One Watt is defined as a rate of transfer of energy equal to 1 Joule per second.

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## Components of Force

Horizontal = F cos theta

Vertical = F sin theta

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## The Principle of Moments

Sum of Clockwise moments = Sum of Anti-clockwise moments

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Speed x time

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## Distance travelled

Area under the line of a speed-time graph

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## Projectile Motion

Horizontal component = initial speed x time

Vertical Component = 0.5 x gravity x time^2

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## Newton's Laws

First Law

Objects either stay at rest or remain in uniform motion in the same direction unless acted on by an external force

Second Law

Force = mass x acceleration

Third Law (Law of Inertia)

Weight = mass x gravity

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## Thinking Distance

The distance travelled in the time it takes the driver to react to the hazard.

Speed x reaction time

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## Braking Distance

The distance it takes for the car to stop completely once the driver has reacted.

v^2 / 2a

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## Stopping Distance

Thinking distance + Braking Distance

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## What factors might affect stopping distance?

• Medication/Drugs
• Alcohol
• Weather
• Tyre conditions
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## What safety features does a car have, and what do

• Vehicle Bumpers
• Airbags
• Collapsible Steering Wheel
• Crumple zones
• Seat Belts

They all increase impact time, which reduces impact force, which lessens the force of the crash on the driver.

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