# P2 topic 9

edexcel 360science

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• Created by: Layla
• Created on: 14-04-11 13:18

## SPEED AND VELOCITY

what is the formula of working out velocity? what is displacement?

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## SPEED AND VELOCITY

average velocity = displacement / t

displacement: the distance in a particular direction

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## ACCELERATION AND VELOCITY-TIME GRAPHS

what is acceleration? what is the unit used?

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## ACCELERATION AND VELOCITY-TIME GRAPHS

- how quickly the velocity is changing

- m/s(squared)

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## FORCES

name the six different types of force and what they do
(learn the force diagrams)

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## FORCES

1) gravity/weight - always acts straight downwards
2) reaction force - from a surface. usually acting straight upwards
3) thrust/push/pull - due to an engine/rocket speeding something up
4) drag/air resistance/friction - slowing the thing down
5) lift - due to an aeroplane wing
6) tension - in a rope/cable

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## FRICTION FORCES AND TERMINAL VELOCITY

describe friction and resistance/drag from fluids (air or liquid)

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## FRICTION FORCES AND TERMINAL VELOCITY

- if an object has no force propelling it along it will always slow down and stop because of friction (unless your in space)
- always acts in the opposite direction of the movement
- to travel at a steady speed: driving force needs to be equal to the frictional forces
- you get friction between two surfaces in contact/when an object passes through a fluid (drag)

- most important factor in reducing drag in fluids is keeping the shape streamlined
e.g. a parachute: high drag
- drag increases as the speed increases (resistance from fluids always increases with speed) therefore a car would use more petrol going at a faster speed than a slower speed.

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## FRICTION FORCES AND TERMINAL VELOCITY

what is 'terminal velocity'? what two main factors affect the terminal velocity of a falling object?

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## FRICTION FORCES AND TERMINAL VELOCITY

after speed increases and the resistance builds up, the free-falling object gradually reduces the acceleration until eventually the resistance force is equal to the accelerating force and then it won't be able to accelerate anymore - (terminal verlocity)

two main factors:
1) shape
2) area

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## FORCES AND ACCELERATION

what does a balanced force mean?

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## FORCES AND ACCELERATION

steady speed and direction - it'll keep moving at the same speed in the same direction

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## FORCES AND ACCELERATION

to keep going at a steady speed, what force must you always have?

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## FORCES AND ACCELERATION

zero resultant (overall) force

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## FORCES AND ACCELERATION

what does a resultant force mean?

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## FORCES AND ACCELERATION

there must be acceleration (unbalanced force) - it will accelerate of produce deceleration in the direction of the force

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## FORCES AND ACCELERATION

finish these sentences:
1) the bigger the force....
2) the bigger the mass....

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## FORCES AND ACCELERATION

1) the greater the acceleration or deceleration
2) the smaller the acceleration

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## FORCES AND ACCELERATION

explain what a reaction force is and where it pops up (give example of a trolley)

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## FORCES AND ACCELERATION

reaction force is - if object A exerts a force on object B, then object B will exert the exact opposite force on object A

e.g. if you push on something like a trolly, the trolley will push back against you just as hard. when you stop pushing, so does the trolley

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## STOPPING DISTANCES

what are the two different parts of the overall stopping distance of a car?

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## STOPPING DISTANCES

1) thinking distance - the distance the car travels in the time between the driver noticing the hazard and applying the brakes

2) braking distance - the distance the car travels during its deceleration whilst the brakes are being applied

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## STOPPING DISTANCES

list the two or three factors which affect each of the two parts of the stopping distance

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## STOPPING DISTANCES

thinking distance: how fast you're going, your reaction time (how dopey you are)

braking distance: how fast you're going, how much mass the car is carrying, how good the brakes are and how good the grip is (road surface, weather and tyres)

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## CAR SAFETY

what effect does an increase in the resultant force have on the momentum of an object?

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## CAR SAFETY

a larger force means a faster change of momentum (greater acceleration)

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## CAR SAFETY

explain how seatbelts, crumple zones and airbags are useful in a crash

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## CAR SAFETY

seatbelts - stretch slightly, increasing the time taken for the wearer to stop which reduces the forces acting on the chest

crumple zones - crumple on impact which increases the time taken for the car to stop

air bags - slow you down more slowly (safer for the body)

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## TAKING RISKS

give two methods of estimating the risk of something happening

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## TAKING RISKS

1) how many times it's happened in the past - 'statistical risk assessment'. the more data, the more accurate this will be
2) use a scientific theory to model the situation, then calculate the probability

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Hey,

These are good... but...

Some of the text doesn't fit on to the cards,

Please can you edit them to make sure that all the text fits on to the card.

Thanks,

Ele - Moderator

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