Physics GCSE As fast as you can

These are Revision Cards for topic 9, As fast as you can for the Edexcel 360 paper.

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• Created by: Georgia
• Created on: 04-11-09 19:35

Speed and Velocity

Speed- How fast you are going (20m/s)

Velocity- How fast You are going in a given direction(30mph north)

Speed = Distance / Time

Velocity = Dispalcement / Time

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Speed Cameras

Why?

To catch speeding motourists, and stop accidents

How?

1. Lines are painted on the Road certain Distances Apart

2. 2 photos of the car are taken at a set interval

3. The distance travelled (calculated from the lines) in this time allows us to calculate the speed.

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Acceleration

Acceleration is how guickly speed or velocity Changes

Acceleration = Change in Velocity / Time

Unit=m/s 2 (squared)

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Velocity Time graphs

Flat Srections represent a steady Speed

Steeper the Graph, Greater Acceleration

Uphill sections are acceleration

Downhill sections are deceleration

Area under the graph is the the distance travelled

A curve means the acceleration is changing

Acceleration = Verical Change /Horizontal Change

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The 6 Forces

1.Gravity or Wieght acting Downwars

2. Reaction Force pushing the object back

3.Thrust/push/pull due to extra force to speed something up

4.Drag/air resistance/ Friction slows things down

5. Lift due to an aeroplane wing

6.Tension like on a rope or cable

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Objects Moving

Stationary Object

All forces in balance, must be equal and opposite (or zero)

All forces in Balance

Acceleration

All forces not in balance, bigger the unbalance, bigger acceleration

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Friction Forces

Friction slows things down

Friction acts in the opposite direction to movement

Friction occures when 2 surfaces meet or when an object passes through a liguid or air

Streamlined objects have reduced Drag/friction

Drag Increases as speed incrreases

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Terminal Velocity

Terminal Velocity is the highest possible speed an object can reach.

Objects reach terminal velocity because the drag is equal to the propelling force, so they can accelerate no more.

Therefore more streamlined objects have a higher Terminal Velocity.

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Balanced and Unbalanced Forces

Balanced Force = Steady Speen

This happens when there is no resultant force

Unbalanced Forces = Acceleration

This happens in the direction of the resultant force. This could be starting, stopping, speading up, slowing down, or changing direction

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Resultant Forces

If there is a resultant Force acceleration (or Deceleration) are produced

Resultant force = mass x acceleration

Bigger force mean greater acceleration or deceleration

bigger mass means smaller acceleration/decelleration

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Reaction Forces

If object A exerts a force on object B the object B must exert an opposite but equal force on object A

This means that is you push something it will push back witht he same force.

If one stops pushing then so will the other.

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Stopping Distances

The main Things that effect braking distance are:

Thinking Distnace

• How fast you are going
• How dopey You are(effected by alcohol tiredness drugs, old age...

Braking Distance

• How Fast you are going
• How heavy the veicle is
• How good the brakes are
• How good the grip is (efefcted by road surface, weather and tyres)
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Momentum

mometum = mass x velocity

greater mass or velocity means greater momentum

Momentum is a Vector quality (it has size and direction)

Force acting = change in momentum / time taken for change to happen

Forces change momentum this shows how to work this out

larger force means greater change in momentum

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Car Safety Features

Crumple ZonesCrumple on impact to increase time it takes car to stop

Seat belts Stretch slightly to increase time taken for wearer to stop. This reduces the forces on the chest

Wearing seatbelts reduce fatalities by 50%

Air Bags-These slow you down more gradually

Air bags reduce fatalities by 30%

Due top Increased safety features half the people die today compared to 1980

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Risks

Risks can be calculated by-

• a scientific model
• How many times ity has occured in the past
• It is best to use a combination of the 2

Risks can be represented as

• Decimals
• Percentages
• Fractions

how do people decide whether to take a risk

• How farmiliar they are with it
• Forced to or choose to
• Age, Personality or personal experiences
• Rewards from doing it
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