Terminal Velocity

D. Crowley, 2008

Terminal Velocity

◼ To understand terminal velocity

2018年10月23日

Terminal Velocity

◼ What are the forces on a skydiver? How do these forces change

(think about when they first jump out; during free fall; and when the

parachute has opened)?

◼ What happens if the skydiver changes their position?

◼ The skydiver’s force (Fweight=mg)

remains the same throughout the

jump

◼ But their air resistance changes

depending upon what they’re doing

which changes the overall resultant

force

Two Most Common Factors that Affect Air Resistance

◼Speed of the Object

◼Surface Area

Air Resistance

◼More massive objects fall faster than less

massive objects

Since the 150-kg skydiver weighs more (experiences a greater force of

gravity), it will accelerate to higher speeds before reaching a terminal velocity.

Thus, more massive objects fall faster than less massive objects because they

are acted upon by a larger force of gravity; for this reason, they accelerate to

higher speeds until the air resistance force equals the gravity force.

Skydiving

◼ Falling objects are subject to the force of gravity pulling them down – this can be calculated by W=mg

Weight (N) = mass (kg) x gravity (N/kg)

◼ On Earth the strength of gravity = 9.8N/kg

◼ On the Moon the strength of gravity is just 1.6N/kg

Positional

◼ What happens when you change position during free-fall?

◼ Changing position whilst skydiving causes massive changes in air

resistance, dramatically affecting how fast you fall…

Skydiving Stages

◼ Draw the skydiving stages

◼ Label the forces

◼ Draw correctly sized force arrows

◼ Write a brief sentence explaining the forces

experienced by the skydiver during the

descent

Skydiving Stages

◼ Stage 1 – after just jumping from the plane the skydiver is not

moving very fast – their weight is a bigger force than their air

resistance, so they accelerate downwards

Skydiving Stages

◼ Stage 2 – eventually the force of the air resistance has increased so

much that it is the same size as the skydiver’s weight – the forces are

balanced and the speed remains constant (this is terminal velocity)

Skydiving Stages

◼ Stage 3 – when the chute opens air resistance increases dramatically:

the air resistance force is much greater than the weight force, so the

skydiver slows down

Skydiving Stages

◼ Stage 4 – as the skydiver slows, the air resistance force from the chute is reduced, until it is the same size as the weight force – the forces are balanced and the speed remains constant (this is a new terminal velocity)

Skydive

Physics of Sky Diving

James Bond and Terminal Velocity

Terminal Velocity

◼ When vehicles and free-falling objects first move they have much

more force accelerating them than resistance which is trying to slow

them

◼ As speed increases resistance builds up – gradually reducing the

acceleration

◼ Eventually the resistance forces is

equal to the accelerating force and

the object remains at a constant

speed (terminal velocity)

Velocity-Time Graph

◼ Can you annotate what the velocity-time graph shows for a

parachute jump?

Velocity-Time GraphVelocity

Time

Speed

increases…

Terminal

velocity

reached…

Parachute opens – diver

slows down

New, lower terminal velocity

reached Diver hits the ground