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