12. Drag, Lift and Terminal Speed

Question 1

Define the term friction

Answer 1

A force that opposes motion

Question 2

Name the 2 main types of friction

Answer 2

1. Contact friction

2. Fluid friction

Question 3

Define the term contact friction

Answer 3

Friction that happens between solid surfaces

Question 4

Define the term fluid

Answer 4

Something that can flow - liquid and gas

Question 5

What is fluid friction also known as?

Answer 5

Drag, fluid resistance or air resistance

Question 6

Name the 3 things affecting fluid friction

Answer 6

1. Force depends on viscosity (thickness) of fluid
2. Force increases as speed increases
3. Force depends on shape of object moving through it - the larger the area pushing against the fluid, the greater the resistance force

Question 7

Name the 3 things you need to remember about frictional forces

Answer 7

1. They always act in the opposite direction to the motion of the object
2. They can never speed things up or start something moving
3. They convert kinetic energy into heat

Question 8

Define the term lift

Answer 8

An upwards force on an object moving through a fluid

Question 9

When does lift happen?

Answer 9

When the shape of an object causes the fluid flowing over it to change direction

Question 10

How does the force of lift act in relation to the direction in which the fluid is flowing?

Answer 10

Perpendicular

Question 11

Name an example of lift

Answer 11

Plane wings

Question 12

When does terminal velocity occur?

Answer 12

When the frictional forces are equal to the driving force

Question 13

Name the 3 main stages of a car reaching terminal velocity

Answer 13

1. Car accelerates from rest using constant driving force
2. As speed increases, resistance forces increase because of things like turbulence. This reduces resultant force on car and thus reduces acceleration
3. Eventually, car reaches speed where resistance forces are equal to driving force. There is now no resultant force and no acceleration, so car carries on at a constant speed

Question 14

What are the 2 main ways of increasing a vehicle’s maximum speed?

Answer 14

1. Increasing the driving force (e.g. increase engine size)

2. Reducing the frictional force (e.g. make body more streamlined)

Question 15

On a velocity-time graph, how is the terminal velocity represented?

Answer 15

A horizontal line

Question 16

On an acceleration-time graph, how is the terminal velocity represented?

Answer 16

Graph is at 0 for acceleration

Question 17

Describe the method of calculating the terminal velocity in a fluid

Answer 17

1. Put elastic bands around the tube of viscous liquid at fixed distance using a ruler
2. Drop ball bearing into tube and use stopwatch to record time at each band
3. Repeat this a few times to reduce effect of random error, using a strong magnet to remove ball from tube each time
4. Calculate times taken by ball bearing to travel between consecutive bands and calculate and average for each reading
5. Use average times and distance between bands to calculate average velocity between each pair of bands

Question 18

What would the results from the terminal velocity in a fluid experiment say?

Answer 18

The average velocity increases at first, then stays constant - this is the ball bearing’s terminal velocity in the viscous liquid being used