Biomechanics- Angular motion Flashcards
Newton’s laws of linear motion can be adjusted to explain the movement of rotating bodies, known as angular motion.
State Newton’s first law of angular motion.
(Total 1 mark)
A body will continue rotating/spinning with a constant angular velocity unless acted upon by an external torque/rotational force. (1)
Accept any other appropriate recollection of Newton’s first law of angular motion.
A. Angular displacement × time ☐
B. Angular displacement / time ☐
C. Angular momentum × time ☐
D. Angular momentum / time ☐
(Total 1 mark)
B
Newton’s laws of linear motion can be adjusted to explain the movement of rotating bodies, known as angular motion.
The figure shows a figure skater rotating in the air during a jump.
Analyse how Newton’s laws of angular motion can account for the figure skater’s speed of rotation throughout the movement.
(Total 3 marks)
* (Newton’s first law of angular motion) The ice skater will rotate with constant angular momentum in the air if there is no external torque/rotational force slowing them down until they land back on the ice. (1)
* (Newton’s second law of angular motion) The more torque/rotational force the skater pushes off the ice the faster they will rotate allowing them to complete their rotations before returning to the ice. (1)
* (Newton’s third law of angular motion) When the rotating figure skater lands back on the ice the torque they apply to ice is returned to them slowing them down. (1)
* (Newton’s third law of angular motion) At take off the ice skater will apply a torque to the ice which will generate torque in the opposite direction causing the skater to rotate. (1)
Accept any other appropriate analysis of how Newton’s laws of angular motion can account for the figure skaters speed of rotation throughout the movement.
Maximum 3 marks
Gymnasts have to change the position of their body when performing a somersault during a gymnastic floor routine.
Explain how a gymnast alters their angular velocity by changing their moment of inertia.
(Total 4 marks)
AAngular momentum = moment of inertia × angular velocity/ (during rotation) Angular momentum remains constant/conservation of angular momentum
BTo slow down (rotation) gymnast increases moment of inertia
CAchieved by extending body/opening out/or equivalent
DTo increase speed (of rotation) gymnast decreases moment of inertia
EAchieved by tucking body/bringing arms towards rotational axis
Max 4 marks
The graph below represents the principle of conservation of angular momentum applied to a gymnast as they perform a front tuck somersault
Analyse how the gymnast makes use of the principle of conservation of angular momentum when performing a front tuck somersault.
Refer to the graph above in your answer. [total 8 marks]
Ao1
* Angular momentum is the quantity of rotation a body possesses, and is a product of moment of inertia and angular velocity/angular momentum = moment of inertia X angular velocity.
* Moment of inertia is a body’s reluctance to rotation/reluctance to alter its rate of rotation.
* Angular velocity is the rate of rotation of a body around its axes of rotation.
* Angular acceleration is the rate of change of angular velocity.
* The principle of conservation of angular momentum states that angular momentum remains constant, if moment of inertia decreases, angular velocity increases and vice versa.
**
AO2: Application of the principle of conservation of angular momentum when the gymnast performs a front tuck somersault.**
* Moment of inertia is high at the start and the end of the somersault but low in the middle of the movement.
* Angular velocity is low at both the start and the end of the somersault but high in the middle.
* Angular acceleration is occurring as the performer begins the somersault, and angular deceleration occurs as they complete the somersault.
* Angular velocity is low at the start and end of the somersault as they go into and come out of the somersault, slowing the rate of rotation.
* Angular momentum remains constant throughout the somersault.
AO3: Analysis of how the principle of conservation of angular momentum affects the gymnast when performing a front tuck somersault.
* The gymnast is in an open position initially, resulting in a large moment of inertia, resulting in a low angular velocity.
* The gymnast gets into a tucked position. As mass is distributed closer to their centre of mass this reduces their moment of inertia and increases their angular velocity/rate of rotation.
* The angular acceleration as a result of the gymnast’s reduced moment of inertia, and increased angular velocity allow a full rotation to occur quickly, allowing the gymnast time to land safely.
* As the gymnast opens out from the tucked position, their moment of inertia increases, mass is distributed further from the centre of mass and angular velocity decreases/angular deceleration, allowing the gymnast to slow down prior to landing, maintaining control.
* Angular momentum remains constant as the gymnast manipulates their body position to reduce moment of inertia and increase angular velocity whilst maintaining angular momentum.
Accept any other appropriate analysis of how the gymnast uses the principle of conservation of angular momentum when performing a front tuck somersault.
The photograph shows a dancer performing a spin as part of a routine
Explain Newton’s Laws of Motion in relation to the dancer spinning and how the dancer can alter her rate of spin.
(Total 8 marks)
AO1 – Knowledge
Identified Newton’s Laws and/or how the dancer can alter her rate of spin using simple statements, eg Newton’s First Law states that that a body will continue to turn about its axis of rotation with constant angular momentum unless an external force is exerted upon it.
AO2 – Application
Explained Newton’s Laws in relation to the dancer and/or how the dancer can alter her rate of spin, eg Newton’s First Law states that a body will continue to turn about its axis of rotation with constant angular momentum unless an external force is exerted upon it. Therefore the dancer will continue to spin with constant angular momentum unless an external force acts on her.
AO3 – Analysis/Evaluation
Linked explanation of Newton’s Laws in relation to the dancer and the rate of spin, eg Newton’s First Law states that that a body will continue to turn about its axis of rotation with constant angular momentum unless an external force is exerted upon it. Therefore the dancer will continue to spin with constant angular momentum unless an external force acts on her. This is known as the principle of conservation of angular momentum. The dancer can alter her rate of spin by moving her limbs either closer or further away from the axis of rotation, therefore to increase her rate of spin she will need to bring her arms close to her body, without the ability to do this she will be unable to control the movement. If she has failed to warm up appropriately she will not be able to achieve the most efficient position, making the spin more difficult to perform and with a reduction in potential oxygen delivery (due to the lack of a suitable warm up) she will fatigue more quickly reducing her ability to control the spin.
Credit other relevant points explaining Newton’s Laws of Motion in relation to the dancer spinning and how the dancer can alter her rate of spin.
