angular motion

Question 1

angular motion

Answer 1

angular motion is movement of a body or part of a body in a circular path about an axis of rotation

Question 2

example of angular motion

Answer 2

• a gymnasts whole body will rotate around the high bar (axis of rotation)
• an athletes legs rotate at the hip point (axis of rotation) as they run
• a trampolinist whole body rotates around their centre of mass during a somersault

Question 3

what does angular motion result from

Answer 3

• angular motion results from an eccentric force being applied to a body the force is applied outside the centre of a body’s mass
• an eccentric force is also known as torque

Question 4

eccentric force

Answer 4

a force applied outside the centre of mass, resulting in angular motion

Question 5

torque

Answer 5

a measure of the turning (rotational or eccentric) force applied to a body

Question 6

what is an axis of rotation?

Answer 6

an imaginary line that passes through the centre of mass about which a body rotates: longitudinal, transverse and sagittal axis

Question 7

what is the longitudinal axis?

Answer 7

axis that runs from head to toe through the centre of mass

Question 8

what is the transverse axis?

Answer 8

transverse axis runs from the left to right through the centre of mass

Question 9

what is the saggital axis?

Answer 9

frontal axis runs from front to back through the centre of mass

Question 10

what is angular motion measured in?

Answer 10

radian (rad)

Question 11

what is radian (rad)

Answer 11

• a unit of measurement of the angle through which a body rotates
• 360 degrees = 2 pi radians, 1 radian = 57.3 degrees

Question 12

angular velocity

Answer 12

angular velocity is the rate of change in angular displacement or simply the rate of rotation

Question 13

equation for angular velocity

Answer 13

angular velocity = angular displacement/time taken

Question 14

practical example of angular velocity

Answer 14

• a trampolinist performing a seat drop rotates their legs clockwise about the transverse axis 1.57 radians in 0.5 seconds
• the average angular velocity is 3.14rad/s (1.57rad/0.5s)

Question 14

equation for moment of inertia

Answer 14

sum of(mass x distribution of the mass from the axis of rotation squared)

Question 14

units for moment of inertia

Answer 14

measured in kilogram metres squared (kgm squared), mass in kilograms and distribution of the mass from the axis of rotation in metres squared

Question 15

what is moment of inertia?

Answer 15

• is the resistance of a body to change its state of angular motion or rotation
• a resting body will not want to start rotating around an axis and a rotating body will not want to change its angular motion or momentum; it will resist increasing or decreasing the rate of spin
• moment of inertia is the angular or rotational equivalent of inertia

Question 16

two factors that affect the moment of inertia are what?

Answer 16

• mass
• distribution of mass

Question 17

explain how moment of inertia has a direct effect on angular velocity

Answer 17

• if moment of inertia is high, resistance to rotation is also high, therefore angular velocity is low: the rate of spin is low
• if moment of inertia is low, resistance to rotation is also low, therefore angular velocity is high: the rate of spin is fast

Question 18

what is angular momentum?

Answer 18

• is the quantity of angular motion possessed by a body
• it is the rotational equivalent of momentum

Question 19

equation for angular momentum

Answer 19

angular momentum = moment of inertia x angular velocity

Question 20

what is conservation of angular momentum

Answer 20

• angular momentum is a conserved quantity which remains constant unless an external eccentric force or torque is applied

Question 21

what is angular analogue of Newtons first Law of motion

Answer 21

• the angular equivalent of Newtons first law of motion, which states: a rotating body will continue to turn about its axis of rotation with constant angular momentum unless acted upon by an eccentric force or external torque