Forces revision

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  • Created on: 15-05-14 18:30
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Forces and Motion
Average speed = total distance ÷ total time
Acceleration = change in velocity ÷ time taken
Acceleration = force ÷ mass
Force = mass x acceleration
Weight = mass x gravity (g)
Moment = force x perpendicular distance from pivot
Velocity = displacement ÷ time
Scalars and Vectors
Vector quantities have direction and magnitude (to remember: Victor is tall [direction] and fat
[size])
Scalars only have magnitude.
E.g. Vector- displacement; scalar- distance, speed. The difference between speed and
velocity is that velocity is speed in a certain direction.
Motion Graphs- Gradients and areas under graphs
Gradient of distance-time graph = speed, Units
of displacement-time graph = velocity, Acceleration= m/s2
of velocity-time graph= acceleration Displacement= distance +
bearing
Area under velocity-time graph= displacement, Velocity= m/s
speed-time graph= distance
Ticker-tape Timers
Speed= distance between all dots ÷ (time between each dot x number of gaps)
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E.g. If the distance between the 9 dots on the above ticker-tape were 4.5cm, and 50 (so 0.02
seconds per dot) dots were made each second, what would the speed be?
Answer: 4.5 ÷ (0.02 x 8)= 25cm/s
Stopping distance
- Made up of thinking distance (between when you think of stopping and put foot on brakes)
and braking distance (from when you put your foot on brakes to when you stop)
- Factors affecting thinking distance: reaction time (tiredness, visibility, level of intoxication),
speed of car
- Factors affecting braking distance: friction of road surface, mass of vehicle, deceleration,
initial speed

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Forces and Motion
Hookes Law
- Extension of a spring/metal wire is proportional to force stretching it (until elastic limit
reached, when it becomes permanently stretched)- as shown by linear region of force-
extension graph
- When a spring returns to original length, exhibits elastic behaviour, when it doesnt, plastic
behaviour
- After force causing elastic deformation is removed, spring returns to original length, after
plastic deformation, it doesnt
- Elastic bands dont follow Hookes law
Forces
- Force = push or pull of one…read more

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