Forces And Motion Flashcards
For parachutists, what happens when the air resistance exactly cancels out the downward force of gravity
The parachute will stay at the same speed as it falls
The forces are balanced at terminal velocity
What does the stopping distance of a vehicle depend on, describe
THINKING DISTANCE-Distance travelled by vehicle from point when driver realises need to brake to when brakes are applied
BRAKING DISTANCE- Distance travelled by vehicle from point when brakes are applied to when vehicle actually stops
When is thinking distance increased
Vehicle is travelling faster
Driver is ill,tired or influenced by substances
Driver is distracted, not concentrating
Poor visibility
When is braking distance increased
Vehicle is travelling faster, higher kinetic energy
Poor weather/road conditions,friction between tyres and road decrease
Vehicle is in poor condition eg brakes, tyres worn out
Smaller braking force applied to brakes
Bigger mass in vehicle, higher kinetic energy
What does a longer thinking and braking distance mean
Vehicle takes longer to stop (longer stopping distance)
What happens as the speed of a car increases
(thinking and braking distance, give figures)
Thinking distance increases linearly (proportionally)
if speed doubles, thinking distance doubles
Braking distance increases as the square of the speed
If speed doubles, braking distance quadruples
If speed trebles, braking distance increases by factor of 9
If forces are opposite and equal what happens to the object
It will move at a constant speed or be stationary
What does proportional mean
There is a direct relationship
Eg. If speed doubles, thinking distance doubles
(It is linearly)
How do frictional forces (such as drag,friction and air resistance) act against the movement of an object
The object’s kinetic energy is reduced and it is slowed down
How can the effect of frictional forces be reduced on an object
Changing it’s shape (increase or decrease air resistance)
Using a lubricant (slide with less resistance)
Why do falling objects speed up as they fall
They are pulled towards the centre of the earth by gravity
What are forces measured in
Newtons (N)
How is force measured
Force=mass X acceleration
A bigger force on a mass will increase its what
Acceleration
