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PE - Green Booklets > Angular motion > Flashcards

Angular motion Flashcards

1
Q

Angular motion (definition)

What does angular motion result from? (2)

A

Movement of a body or part of a body in a circular path about an axis of rotation.

  • Angular motion results from an eccentric force being applied to a body
  • Also known as ‘torque’ (measure of a turning force applied to a body). It is applied to the outside of the COM
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2
Q

Linear motion
Definition -
Created by - (2)
Sporting Example -

Angular Motion
Definition -
Created by - (2)
Sporting Example - (2)

A

Linear motion
Definition:

     - Linear motion is movement of a body in a straight or curved line, where all parts move the same distance in the same direction over the same time

Created by:

     - Direct force
     - An external force through the centre of mass

Sporting Example:

     - Skeleton bob at top speed

Angular Motion
Definition:

     - Angular motion is movement of a body in a circular path about an axis of rotation

Created by:

     - Eccentric force
     - An external force passes outside the centre of mass

Sporting Example:

     - Gymnastic somersault
     - Drive and recovery leg rotating around the hip joint
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3
Q

Principal axes of rotation (definition)
What are they and give an example for each

A

A principal axis of rotation is an imaginary line that passes through the centre of mass about which a performer can rotate

Transverse axis:

  • Runs from left to right through the centre of mass
  • Example: front somersault

Frontal axis:

  • Runs horizontally through the centre of mass (from front to back)
  • Example: cartwheel

Longitudinal axis:

  • Runs vertically (head to toe) through the centre of mass
  • Example: spin in ice skating, full turn in trampolining
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4
Q

Angular analogues of Newton’s laws of motion

It is possible to relate Newton’s laws of motion to angular motion, by simply changing the terminology. Remember this time it is …

A

an eccentric reaction force that causes a change to angular motion.

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5
Q

Angular analogues of Newton’s laws of motion - NL1

What is it?
Sporting Example?

A

A rotating body will continue to turn about its axis of rotation with constant angular momentum unless an external force (torque) acts upon it

Sporting example: ice skater spinning in the air, they will continue to spin until they land on the ice. When an external force (torque) is exerted from the ice on their skates. This will change their state of angular motion

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6
Q

Angular analogues of Newton’s laws of motion - NL2

What is it?
Sporting Example?

A

Rate of change of angular momentum of a body is proportional to the force (torque) causing it and the change that takes place in the direction which the force (torque) acts

Sporting example: the greater the torque exerted the faster the reaction will be, ice skater starting their spin.

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7
Q

Angular analogues of Newton’s laws of motion - NL3

What is it?
Sporting Example?

A

When an eccentric force (torque) is applied by one body to another, the second body will exert an equal and opposite force (torque) on the other body

Sporting example: GK tips the ball over the bar. They throw their arms up (eccentric action force), this causes the lower part of their legs to go back (reaction force)

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8
Q

Calculations and measurements

There are three key descriptors important to angular motion these are:

A
  • Angular velocity
  • Moment of inertia
  • Angular momentum
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9
Q

Angular velocity

Definition
Formula
Measured in

A

The rate of change in angular displacement OR simply the rate of rotation

Angular velocity = angular displacement/time taken

Measured in radians per second (rad/s)

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10
Q

Moment of inertia

Definition
Formula
Measured in

A

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

Moment of inertia = sum of (mass x distribution of mass from the axis of rotation2)

Measured in kilogram metres2 (kgm2)

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11
Q

Factors that affect moment of inertia and their description

A

Mass:

      - The greater the mass of the body, the greater the moment of inertia. 

      - Low mass decreases moment of inertia and resistance to change state of rotation

Distribution of mass from axis of rotation:

      - The further the mass moves from the axis of rotation the greater the moment of inertia and vice versa
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12
Q

Can you apply the factors that affect the moment of inertia to running? (use the image below to help you)

A

The recovery leg’s mass is distributed close to the axis of rotation at the hip, therefore, moment of inertia is low. Resistance to rotation is low and the leg moves back to the ground quickly

The drive leg’s mass is distributed from the axis of rotation, therefore, moment of inertia is high and the leg moves slowly

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13
Q

Moment of inertia has a direct effect on angular velocity - high vs low

A

High moment of inertia:

   - Resistance to rotation is also high
   - Angular velocity is low
   - Rate of spin is slow

Low moment of inertia

   - Resistance to rotation is low
   - Angular velocity is high
   - Rate of spin is fast
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14
Q

Angular momentum

Definition
Formula
Measured in

To start rotating around an axis angular momentum must be generated. In the preparation or take off phase of a rotational movement pattern an ___________ force or _______ must be applied

A

The quantity of angular motion possessed by a body

Angular momentum = moment of inertia X angular velocity

Measured in kilogram metres2 rad/s (kgm2 rad/s)

To start rotating around an axis angular momentum must be generated. In the preparation or take off phase of a rotational movement pattern an eccentric force or torque must be applied

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15
Q

Practical example - angular momentum

60 kg gymnast performs a tuck front somersault.

Tuck phase moment of inertia = 15kgm2

Rotation has an angular velocity of 8.0 rad/s

Angular momentum = ?

A

Angular momentum = 120kgm2 rad/s

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16
Q

Application of angular momentum using springboard diver (5)

A
  1. A springboard diver must jump away from the board and create rotation.
  2. They lean away from the board so that a reaction force is generated from the platform
  3. It also passes outside their COM (leaning back creates a spinning effect)
  4. This creates an eccentric force and generates angular momentum
  5. Greater the size of the eccentric force applied to the body the greater the quantity of angular momentum generated
17
Q

Conservation of angular momentum

Defined as:

A

Angular momentum is a conserved quantity which remains constant unless an external force (torque) is applied.

18
Q

Example of graph

  1. At take off the diver generates angular momentum by an ___________ _____ from the springboard acting on the body (_________) and starts rotation about the ____________ axis.
  2. The straight body position ____________ mass away from the transverse axis. Moment of inertia is _____ (______) and angular velocity is ___ (_______) the diver rotates _________ and goes into the dive with control.
  3. During flight the divers tucked position distributes mass _______ to the _____________ axis. Moment of inertia is _____________ and angular velocity ____________. This diver rotates quickly enabling one-and-a-half rotations in the flight time.
  4. Preparing to land, the divers straightened body position distributes _____ away from the ____________axis. Moment of ________ is ____________ and angular velocity ___________. The rate of spin __________ gaining control for entry into the water.
  5. Angular momentum is ___________ throughout the movement.
A
  1. At take off the diver generates angular momentum by an eccentric force from the springboard acting on the body (50kgm2 rad/s) and starts rotation about the transverse axis.
  2. Straight body position distributes mass away from the transverse axis. Moment of inertia is high (15kgm2) and angular velocity is low (3.3 rad/s) the diver rotates slowly and goes into the dive with control
  3. During flight the divers tucked position distributes mass close to the transverse axis. Moment of inertia is decreased and angular velocity increased. The diver rotates quickly enabling one and half rotations in the flight time.
  4. Preparing to land, the divers straightened body position distributes mass away from the transverse axis. Moment of inertia is increased and angular velocity decreases. The rate of spin decreases gaining control for entry into the water
  5. Angular momentum is conserved throughout the movement.

PE - Green Booklets (39 decks)

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