(1.21) Terminal Velocity

What forces do falling objects experience?

Weight (due to gravity)

Air resistance or drag (due to friction)

What is the effect of speed on air resistance? Why?

The faster the speed, the higher the air resistance.

More particles collide in a given time

What is the effect of mass on a falling object’s terminal velocity?

The less massive an object,

the faster they will reach terminal velocity

as they do not have to accelerate as much for drag to = weight.

This means that the force on the less massive object will be smaller

as the ground will have to exert less force to get their force to zero.

Why is it that the faster an object falls, the greater the resistance against the object?

If speed were to double, twice as many particles would need to be moved aside per second, so the drag should also double.

The object would also be hitting each particle twice as hard because each collision need to result in twice the change in momentum of the particle.

Per Newton’s second law, this will produce an additional doubling of the drag.

So, if speed were to double, drag would quadruple.

What is terminal velocity?

The constant speed a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration.

Describe what happens when someone jumps from a plane in terms of force and acceleration.

They initially accelerate downward due to their weight.

As they accelerate, the air resistance increases until it eventually

grows large enough to balance the force of their weight.

Describe what happens when some jumps from a plane in relation to resultant + balanced forces.

Initially, the upwards air resistance is very low as they are not falling quickly, so the forces are unbalanced and the weight of the diver is the greater force.

As they speed up, air resistance increases and balances the force downward, meaning there is no longer any resultant force.

The diver’s acceleration is zero and they are at terminal velocity.