Key Areas covered Terminal velocity. Velocity-time graph of a falling object when air resistance is taken into account, including the effect of changing surface the area of the falling object.

What we will do today: Revise what is meant by terminal velocity. Draw a v-t graph for a parachutist jumping from a plane until they reach the ground.

Animation showing parachute journey

Terminal velocity When an objects falls towards the Earth it has two vertical forces acting on it.

Terminal velocity As the object falls towards Earth it’s velocity increases (due to the acceleration of gravity). When the speed of an object increases so does the air resistance acting against it. Eventually the two forces will balance out and the object will no longer accelerate (balanced forces = constant velocity). This constant velocity is known as terminal velocity.

Graph of terminal velocity

Parachutes When doing a parachute jump, the parachute is released to increase the surface area and as a result, the air resistance (friction) increases. This slows the parachutist’s velocity allowing them to land safely.

Parachutists v-t graph

Free-fall (1) Free-fall is defined as motion where the only force acting on the object is weight due to gravity. However, we can consider free fall as being the absence of force between two objects both falling at the same time due to gravity (without any external forces) – often described as weightlessness. In these examples, we ignore air resistance (forces due to friction)

Physics of Free Fall Ride Previously examples using the equations of motion assume free fall. Free-fall can also be observed practically in situations where friction does not exist e.g. space: Or on carnival rides: Brian Cox – Human Universe: Free Fall in a Vacuum Physics of Free Fall Ride