Motion of mass on a parachute Falling objects increase their speed

as they fall. This is due to their weight (the

force of gravity) that pulls them to the earth

They also experience an upward force called air resistance (drag), which slows them down.

Graph showing the motion of a skydiver

Terminal Velocity

When an object falls, it will accelerate towards the Earth, due to the force of gravity acting on it. This force can also be called weight.Frictional forces between the air and the object will act in the opposite direction.The faster the object falls, the more air it passes through, so air resistance, or drag, gradually increases.If the falling object has a large surface area, the force of friction will be greater.

A parachute provides a large surface area.

When the force of friction acting upwards equals the force of gravity acting downwards on the object, the resultant force will be zero.The object then falls at a steady speed.This speed is called the terminal velocity.

When a vehicle has a steady speed, the driving force of the engine is equal to the frictional forces due to the air and the road.

Stokes LawF = 6 πηr vF is the drag force from

the parachuter is the radius of the

parachutev is the velocity at which

the parachute fallsη is the viscosity of the air

r

Fv

Stokes LawIf the parachute is falling at a steady speed (terminal velocity)Weight of payload = 6 πηr vT

Weigh = mgmg = 6 πηr vT

RearrangingvT = mg/6 πηr

vT should be proportional to m.

vT6 πηr vT

mg