# Physics- P4 Revision

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## Equations

• Acceleration= Change in Velocty/Time,
• Speed= Distance/Time,
• Velocity= Displacment/Time,
• Wight= Mass*Gravitaion Field Strenght,
• Force= Mass*Acceleration,
• Momentum= Mass*Velocity,
• Gravitatinol Potential Energy(GPE)= Maa*Gravitatnol Field Strenght*Height,
• Kinetic Energy= 0.5*Mass*Velocity2,
• Power= Work Done/Power,
• Final Velocity2= (Inital Velocty)2+(2*Acceleration*Distance),
• Moment= Force*Distance from piviot,
• Total Stopping Time= Thinking Distance+Braking Distance,
• Reaction Time= 2*Reaction Distance/10,   (Square root the answer),
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Gravitation,
Elastic,
Electric,
KInetic,
Sound,

Light,
U--
Nuclear,
Chemical,
Heat,

Key

Can be stored

Can't be stored

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## The Principle of......

The Principle of Conservation Energy

• Energy cannot be created or destroyed but can be transferred from 1 type to another,
• Another name for energy transferred is work done,

The Principle of Moments

• If the anti-clockwise moment & clock-wise moment are equal, then the trebuchet is balanced,
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## Collision Time

The greater the time to stop the smaller the force felt, this time is often called the collision time.

Examples where increased collision time reduces forces:

• Bending elbows to catch a ball,
• Airbags,
• Vertical Seat Belts,
• Crumple Zones,
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## Gravity & GPE

Gravity acts toward the center of the earth.

The GPE on the earth is 10N/kg,

The GPE on the moon is 1.6N/kg,

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## Typical Speeds

• Speed of Light= 300,000,000m/s,
• Speed of Sound= 330m/s,
• Wind- Gental Breeze- 5m/s,
Strong Breeze- 12m/s,
• Walking- 4km/h --  1m/s,
• Cycling- 24km/h -- 6m/s,
• Running- 16kh/h -- 4m/s,
• Car in Town- 48km/h -- 12m/s
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## Newtons Laws

Newtons 1st Law

A stationary object, with no resultant force, will keep still,
A moving object, with no resultant force, will keep moving at a constant speed,

Newtond 2nd Law

A stationary object, with a resultant force, will start moving,
A moving object, with a resultant force, will speed up/ slow down or change direction,

Newtons 3rd Law

If object A exerts a force on object B, then object B exerts an equal but opposite force on object A,

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## Meanings

• Acceleration can mean: Speeding up, Slowing Down or Changing Direction,
• Displacement: Shortest distance between 2 points,
• Mass is the amount there is of something,
• Weight is the amount of force on something,
• Momentum is a vector quantity, meaning it has a direction and a speed,
• Power is the rate at which work is done,
• The turning effect of a force is called a moment,
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## Circular Motion

• Any object needs a force to travel in a circle,
• The eath goes at a constant speed, not a constant velocity,
• The speed may be constant but the velocity changes because it is going in a different direction,
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## Inertial Motion

The reluctance of a body to start moving, a force is needed to start something moving.

Mass= Force/ Acceleration.

Example

A lorry of mass 20,000kg traveling at 108km/h braked and stops in 102m.
Calculate: a- Deceleration= -3.75m/s,
b- Braking Force= -75,000N,

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