# Physics P4

Double award Physics module 4

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## P4

Units

mph (imperial)

km/hr (metric)

decimal hours - 30 mins = 0.5 hours

Speed Equation

speed = distance travelled / time taken

m/s = m / s

Average Speed - if you have a long journey, the final distance and time will give you an average speed

Instantaneous Speed - the speed you are doing in that instant

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## P4.2

Displacement - the distance between the starting point and object in a particular direction (not distance journied)

Distance-Time graphs

steeper the line - faster

Velocity - speed with a direction

Accelerates - speeding up

Decelerates - slowing down

Average acceleration equation

average acceleration = change in speed / time taken for change

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## P4.2

Speed - time graph

upward slope - accelerating

downward slope - decelerating

straight line (not on/near to horizontal) - constant speed

straight line (near to horizontal) - slow

straight line (on horizontal) - stationary

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## P4 - Forces

7 types

• gravity
• friction
• air resistance
• magnetic
• normal reaction
• upthrust
• lift

measured in Newtons (N)

Newtons third law of Motion

when two objects interact, each experiences a force. The two forces are equal in size but opposite in direction.

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## P4 - Forces/Energy

Interaction pairs of forces

1. one force acts on one object, one force acts on the other
2. opposite directions
3. forces are equal in size

Energy

Energy is measured in Joules, J

9 types

kinetic sound nuclear

elastic light electrical

heat chemical gravitational potential

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## P4 - Energy

Kinetic energy equation

KE = 1/2 mass x velocity^2

J = 1/2 kg x m/s^2

Gravitational potential equation 100g = 1N

GPE = weight x height 1 kg = 10N

J = N x m

Work equation

Work = force x distance

J = N x m

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## P4 - Other equations

Momentum

momentum = mass x velocity

kgm/s = kg x m/s

Change in Momentum

change in momentum = force x time

kgm/s or Ns = N x s

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