Angular motion, projectile motion and fluid mechanics

Question 1

What is angular motion?

Answer 1

Movement around a fixed point or axis.
Occurs when force is applied outside the centre of mass. (eccentric force)

Question 2

What is torque?

Answer 2

A turning force, that causes an object to turn about its axis.
It causes angular motion.
Moment of torque (nm) = force x perpendicular distance from the fulcrum.

Question 3

What is Newton’s first analogue?

Answer 3

A rotating body will continue to turn about its axis of rotation with constant angular momentum unless an external torque is acted.
An ice skater will continue to spin in the air until they land when an external torque is acted on their skates.

Question 4

What is Newton’s second analogue?

Answer 4

The rate of change of angular momentum of a body is proportional to the torque causing it and the change takes place in the direction in which the torque acts.
The greater the torque exerted, the faster the rotation.

Question 5

What is Newton’s third analogue?

Answer 5

When a torque is applied by one body to another, the second body will exert an equal and opposite torque on the other body.

Question 6

What is angular displacement?

Answer 6

The smallest change in angle between the starting and finishing point.
Measured in degrees (57.3 radians).

Question 7

What is angular velocity?

Answer 7

The rotational speed of an object and the axis about which it is rotating.
(rad/s) = angular displacement / time taken

Question 8

What is angular acceleration?

Answer 8

The rate of change of angular velocity.
(rad/s^2) = change in angular velocity / time taken.

Question 9

What is moment of inertia?

Answer 9

The resistance of a body to angular motion.
At the start of rotation the body resists angular motion, but once rotation occurs, the body wants to continue about its axis.

Question 10

How does the mass affect moment of inertia?

Answer 10

The greater the mass, the greater the resistance to change and therefore greater moment of inertia.

Question 11

How does distribution of mass from the axis of rotation affect moment of inertia?

Answer 11

The closer the mass to the axis of rotation, the easier it is to turn, because moment of inertia is low.
A somersault in an open position has a higher moment of inertia than a tuck because the distribution of mass is further from their axis of rotation, and faces more resistance.

Question 12

What is angular momentum?

Answer 12

The quantity of rotation a body possesses or just spin.
Angular momentum = moment of inertia x angular velocity.

Question 13

What is conservation of angular momentum?

Answer 13

It stays constant unless an external torque acts upon it.
When a diver performs a somersault, the amount of angular momentum stays the same during flight and only changes when the diver hits the water or changes position.

Question 14

What is projectile motion?

Answer 14

The movement of an object or human body as they travel through the air.
Horizontal displacement is affected by angle, speed, and height of release.

Question 15

What is horizontal displacement?

Answer 15

The shortest distance from the starting point to the finishing point in a line parallel to the ground.

Question 16

How does angle of release affect horizontal displacement?

Answer 16

The optimum angle is dependent on the release height and landing height.
When equal, the optimum angle is 45°.
E.g. long jumper.
Release height below landing height = greater than 45°. e.g basketball shot.
Release height above landing height = less than 45° e.g. shot putt.

Question 17

How does speed of release affect horizontal displacement?

Answer 17

The greater the release velocity, the greater the distance travelled.

Question 18

How does height of release affect horizontal displacement?

Answer 18

A greater release height results in greater horizontal displacement.

Question 19

What factors affect flight paths of projectiles?

Answer 19

Projectiles with large weight force and little air resistance are parabolic. e.g. shot put.
A larger air resistance and less weight force causes distorted parabola. e.g. shuttlecock.

Question 20

What are the vector components of parabolic flight?

Answer 20

For a shot put:
A large positive vertical component on release and the shot travels up and away.
No vertical component at the highest flight point.
Larger negative vertical component before landing due to gravity.

Question 21

What are fluid mechanics?

Answer 21

The study of an object or body that travels through any liquid or gas.

Question 22

What is drag force?

Answer 22

A dynamic fluid force.
It slows something down - the resistance force caused by the motion of a body travelling through a fluid.
It acts in opposition to the direction of motion.

Question 23

What is surface drag?

Answer 23

Relates to friction between the surface of an object and the fluid environment.
Swimmers wear smooth clothing to reduce surface drag.

Question 24

What is form drag?

Answer 24

Relates to the impact of the fluid environment on an object.
The forces affecting the leading edge of an object increase form drag and the forces affecting the trailing edge reduce it.
Swimmers have thin form to decrease drag.

Question 25

How does velocity of the moving body affect drag?

Answer 25

The greater the velocity of a body through fluid, the greater the drag force.
Streamlining can reduce the effects of drag.

Question 26

How does the cross-sectional area of the body affect drag?

Answer 26

A large cross-sectional area increases drag.
Speed skiers reduce drag by crouching low, and so travel faster.

Question 27

How can drag be reduced?

Answer 27

Speed skier helmets extend to their shoulders to make them more streamlined, and their suit and aerodynamic boots also.
Cyclist’s clothing has ridging, and an aerodynamic helmet with air ducts to reduce drag.

Question 28

What is lift force?

Answer 28

It enables an object to stay in the air for longer, therefore increasing the horizontal distance it travels.

Question 29

What is the Bernoulli principle?

Answer 29

Air that travels faster has a lower air pressure than air that travels slower.

Question 30

What is angle of attack?

Answer 30

It changes the flow of air around the object so the air that travels over the top has to travel a longer distance than the air underneath. So the air on top travels faster, and creates a lower pressure.
This lower pressure creates an upward lift force.

Question 31

What is downward lift force?

Answer 31

Cars, bikes and skiers need to be pushed into the ground so a greater frictional force is created.
In an F1 car, the spoiler is angled so air travelling over the top travels a shorter distance and so travels slower and at a higher pressure.
The car can maintain high speed around corners.