Terminal Velocity

D. Crowley, 2008 2018年10月23日

Terminal Velocity

◼ To understand terminal velocity 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 Graph

Parachute opens – diver Speed slows down increases…

Terminal velocity

reached… Velocity

New, lower terminal velocity Time reached Diver hits the ground