Terminal Velocity
In I/GCSE Physics, an object moving through the air experiences air resistance or drag. The size of this depends on the object’s shape and speed. Objects falling through the air experiences two significant forces: weight and drag.
When an object has just been released, there is a starting velocity of 0m/s. This means there is no drag. The resulting downward acting force is just the weight force of the Earth.
When it starts moving, it has a drag force acting against it, m. As the object is accelerating, it is getting faster. The faster the object moves, the bigger the drag force is.
The object then reaches a point where the drag force exactly balances the weight force. Acceleration is now at zero and the falling object is moving a constant speed. The object has reached terminal velocity as stated in the I/GCSE physcis curriculum.
When a skydiver jumps off the plane, she will accelerate until she reaches terminal velocity. When her parachute opens, it will cause a sudden increase in drag force. This means that there will be an unbalanced force acting upwards, causing her to decelerate. As she slows down, the drag force decreases and a new terminal velocity is reached.
Thinking Distance and Braking Distance
In I/GCSE physics, by definition, thinking distance is the time taken for the driver to respond or react. This can be increased if the driver is tired, under the influence of alcohol/drugs or there is poor visibility.
Braking distance is the distance taken for the vehicle to decelerate to rest after the driver has hit the brakes. This can be increased if the road is slippery or the tyres are screwed up.
Vehicles with a larger mass will have smaller rates of deceleration as you can see in F = ma
Rearranging the equation gives a = F/m. If the braking force of two cars, one that weighs 1000kg and one that weighs 1500kg for example, then the car with the bigger mass will come to rest at a longer time than the other car.
Similarly if a car is breaking from higher velocity, it takes longer to stop
End of this topic!
