# Forces revision

- Created by: Sophie
- Created on: 15-05-14 18:30

First 274 words of the document:

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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