Module 3 - Section 2 - Drag And Terminal Veolvity

Question 1

What is friction ?

Answer 1

it is a force that opposes motion

Question 2

What are the two main types of friction ?

Answer 2

contact friction between solid surfaces

fluid friction - known as drag or fluid resistance or air resistance

Question 3

What does fluid mean ?

Answer 3

it is something that can flow - either a liquid or gas

Question 4

What does the force of fluid friction depend on ?

Answer 4

the force depends on the thickness ( or viscosity ) of the fluid

Question 5

What happens to the drag force as speed increases ?

Answer 5

As speed increases - drag increases

Question 6

Does drag depend on the shape and size of the object moving through it ?

Answer 6

yes, the larger the area pushing against the fluid, the greater the resistive force

Question 7

in what direction do frictional forces always act ?

Answer 7

They always act in the opposite direction to the motion of the object

Question 8

can frictional forces ever speed things up or start moving something

Answer 8

No

Question 9

What do frictional forces convert kinetic energy into ?

Answer 9

frictional forces convert kinetic energy into heat

Question 10

What is terminal velocity ?

Answer 10

It is when the friction force equals the driving force

Question 11

What do you have to have in order to reach terminal velocity ?

Answer 11

You will reach terminal velocity at some point if you have:

• a driving force that stays the same all the time
• a frictional force or drag force that increases with speed

Question 12

What are the 3 main stages to reaching terminal velocity ?

Answer 12

1) the car accelerates from rest using a constant driving force

2) As the velocity increases, the frictional forces also increase - this reduces the resultant force on the car and hence reduces its acceleration

3) Eventually the car reaches a velocity at which the resistance forces are equal to the driving force. There is now no resultant force and no acceleration - so the car carries on at a constant velocity

Question 13

You have to know the velocity time graph for terminal velocity and acceleration time graph for terminal velocity

Answer 13

The velocity time graph starts from zero curves up to right and then flatterns out

the acceleration time graph starts from top left and then curves down right and then flatterns out at right

Question 14

when something is falling through the air, what does the weight of the object act as ?

Answer 14

the weight of the object is a constant force accelerating the object downwards

Question 15

When something is falling through the air what is the frictional; force ?

Answer 15

air resistance opposes the motion when something is falling down and this increases with speed

Question 16

what happens when a skydiver leaves a plane ?

Answer 16

A skydiver leaves a plane and will accelerate until the air resistance equals his weight

he will then be travelling at terminal velocity

the parachute then is deployed to increase the air resistance massively so that now it is bigger than his weight

this slows him down until his speed has dropped enough for the air resistance to be equal to his weight again - this new terminal velocity is small enough to survive the landing

Question 17

how can you measure the terminal velocity of a ball bearing ?

Answer 17

1) put elastic bands around the tube of