Biomechanics - Kinetic Angular Concepts (Unit 3 AOS 1 Terms)

Question 1

ANGULAR CONCEPTS

Answer 1

Torque

Newton’s laws of angular motion

Moment of inertia

Angular momentum

Conservation of angular momentum

Question 2

Kinetics meaning

ANGULAR CONCEPTS

Answer 2

the study of forces that cause motion

Question 3

Difference (definitions) between linear and angular motion

ANGULAR CONCEPTS

Answer 3

Linear motion:
The motion of a body along a straight or curved path

Angular motion:
movement around an axis (internal or external).

Caused by an eccentric force

Internal Axis (Joints)
External Axis (Parallel bars)

Question 4

Torque

ANGULAR CONCEPTS

Answer 4

Def:
A rotational force (push or pull) that makes an object rotate.

The further force is applied from the axis of rotation, the greater the rate of spinning

In sport the closer the body parts are to axis of rotation (> mass around axis of rotation) the higher the velocity.

from axis of rotation
Torque is used to describe force in angular motion the same way ‘force’ is used to describe linear motion.

Question 5

What is an eccentric force

Answer 5

a force thay does not travel through the centre of gravity and will result in roation/spinning

Question 6

Newton’s Laws of Angular Motion

ANGULAR CONCEPTS

Answer 6

(replace force with torque for angular motion)

First Law of Angular Motion:
The angular momentum of a body remains the same unless acted upon by an external torque.

Second Law of Angular Motion:
A torque applied to an object will produce a change in angular motion in the direction of the applied torque that is directly proportional to the size of the torque and inversely proportional to the moment of inertia of the object.

Third Law of Angular Motion:
For every torque there is an equal and opposite torque.

Question 6

Soccer example of torque

ANGULAR CONCEPTS

Answer 6

When you try and bend the ball, an eccentric force is applied resulting in ANGULAR MOTION = TORQUE = ANGULAR VELOCITY

Greater force applied further away from centre of gravity results in more sidespin or ‘bending/curve’

Question 7

Moment of Inertia ( is inertia but in angular motions)

ANGULAR CONCEPTS

Answer 7

The tendency of the body to resist changes in its rotary motion.

The location of the mass is important in increasing or reducing an object’s moment of inertia.
An object whose mass is located closer to the axis of rotation is easier to rotate than one whose mass is further away.

Question 8

how does increasing or decreasing moment of inertia speed up or slow down rotation?

ANGULAR CONCEPTS

Answer 8

Increase rotation:
By increasing the radius from the axis of rotation, the moment of inertia increases thus slowing down the speed of rotation.

Increasinbg speed of roatation:
decrease the radius by bringing body parts closer to the axis of rotation, thus decreasing the radius and moment of inertia

Question 9

big bat small bat and moment of inertia example

ANGULAR CONCEPTS

Answer 9

Small Bat:
Lighter (smaller mass)
Shorter (smaller radius)
Lower moment of inertia
Less reluctant to rotate
Easier to swing

Big Bat:
Heavier (bigger mass)
Longer (bigger radius)
High moment of inertia
More reluctant to rotate
Harder to swing

Mass X radius2

Question 10

Angular Momentum

ANGULAR CONCEPTS

Answer 10

Def:
The quantity (amount) of rotation of a body around an axis.
Angular momentum = moment of inertia x angular velocity.

Question 11

How does increasing the moment of inertia impact angular velocity?

ANGULAR CONCEPTS

Answer 11

An object whose mass is located closer to the axis of rotation is easier to rotate than one whose mass is further away.
Therefore if the dancer, skater or diver brings their mass away from their axis of rotation they will INCREASE their moment of inertia which will result in a DECREASE in angular velocity.

Question 12

Conservation of Angular Momentum

ANGULAR CONCEPTS

Answer 12

when no external force acts on an object, no change of angular momentum will occur.

So once airborne –Angular Momentum WILL NOT CHANGE (this is what conserved means!)
EXAMPLE: In the run up, prior to the somersault, the athlete increases their velocity, which allows them to build linear momentum, which is then transferred into angular momentum for when they begin their forward somersault.

Question 13

Conservation of Angular Momentum

ANGULAR CONCEPTS

Answer 13

Angular momentum is conserved when the body is in flight (stays the same).

As the angular velocity increases (tuck), the moment of inertia will decrease.
The moment of inertia can be decreased by decreasing length of the lever.

This will increase the angular velocity= faster spin

The moment of inertia can be increased by increasing the length of the lever (pike)

This will decrease the angular velocity = slow down

Question 14

Force

Answer 14

Force is the product of mass and acceleration

A force can have either a pushing or pulling effect on a body with mass.

All forces produce or change movement.

Forces cause objects to accelerate (speed up, slow down or change direction)

Question 15

equations
1. force
2. momentum
3. Impulse
4. Moment of Inertia
5. Angular momentum
6. Change in momentum = change in impulse
7. torque

Answer 15

Force = Mass x acceleration

Momentum = Mass (kg) x velocity (m/s)
- same as (p = mv)

Impulse = force x time
- same as (I = Ft)

Moment of Inertia = mass x radius2

Angular momentum = moment of inertia x velocity
- if moment of inertia increases, angular velocity decreases and vice versa to keep angular momentum the same

Change in momentum = change in impulse (△Ft = △mv)

Torque = force x distance from axis of rotation

Question 16

Look at 8 marker sheet (the front-flip sheet)
and do some 8 marker practises