Physics GCSE As fast as you can
These are Revision Cards for topic 9, As fast as you can for the Edexcel 360 paper.
- 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
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.
Acceleration
Acceleration is how guickly speed or velocity Changes
Acceleration = Change in Velocity / Time
Unit=m/s 2 (squared)
Velocity Time graphs
Gradient = Acceleration
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
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
Objects Moving
Stationary Object
All forces in balance, must be equal and opposite (or zero)
Steady Velocity
All forces in Balance
Acceleration
All forces not in balance, bigger the unbalance, bigger acceleration
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
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.
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
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
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.
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)
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
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
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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