P3g: Falling safely

A falling object is pulled downwards by its weight due to gravity.
On Earth all objects accelerate at g= 10m/s2.
g is unaffected by atmospheric changes but varies slightly over the surface of the Earth because it is not perfectly spherical.
At the poles the radius is slightly less so the pull towards the centre is slightly stronger.
Air resistance causes objects to accelerate more slowly.
Larger surface areas experience more air resistance.
As objects speed up the air resistance becomes larger as they displace more air molecules every second.
On the moon there is no atmosphere, so no air resistance.
When a parachute is opened, the air resistance suddenly increases, causing deceleration.
Eventually the parachute will reach a lower terminal speed when the new drag = weight.
Streamlining reduces drag which allows a higher terminal speed (faster top speed) and improves fuel consumption.
Falling objects increase their speed as they fall because their weight (the force of gravity) pulls them to Earth. They also experience air resistance, a frictional force that slows them down.
Objects fall faster until they reach their terminal speed, which is reached when the upward (air resistance) and downward (weight) forces are equal
As they fall through the air, they also experience an upward force called air resistance (drag).
Frictional forces such as air resistance, friction and drag act against the direction of motion, so tend to slow the object down. Objects with large surface areas, such as parachutes, fall more slowly because they experience more air resistance.
Examples of reducing frictional force by streamlining include:
1. A sports car is wedge-shaped to reduce air resistance and so increase top speed
2. Lorries and caravans have deflectors to reduce both air resistance and fuel consumption
3. A downhill skier puts wax on their skis to reduce friction and so increase the top speed.
A skydiver can change their terminal speed by adjusting their shape and position as they fall. For example:
1. If they go head down with their arms by their sides, the air resistance is reduced. Their speed increases until a new, faster terminal speed is reached
2. If they are spread-eagled, the air resistance is increased. Their speed decreases until a new, slower terminal speed is reached.
Cars and other vehicles have a ‘top speed’ – the terminal speed when the driving force from the engine is at its maximum. As the driving force from the engine increases, the speed of the vehicle will increase but so will air resistance.
The factors affecting the terminal speed of a falling object include:
1. its mass
2. the acceleration due to gravity, g.
3. its surface area
on the moon there is no drag on falling objects when there is no atmosphere. This means that the acceleration of falling objects due to gravity is the same whatever their mass and shape.

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P3g: Falling safely

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