Angular Motion Flashcards
Define Angular Motion and how does it occur?
Movement around a fixed point. It occurs when a force is applied outside the centreof mass. An eccentric force is applied.
Give 3 sporting examples when a force is applied outside the centre of mass of an object or body to cause rotation.
Free kick in football so the ball swerves around the wall
Back spin on a netball shot
Top spin in tennis
For each axis of rotation at the shoulder joint what movement occurs
Transverse - Flexion
Sagittal axis - abduction
Longitudinal axis - horizontal abduction.
Expalin, using Newtons first law of angular motion, how a performer can alter their state of rotation
Landing on a trampolining after perfroming a double somersault. The performer continues to rotate until they land on the trampoline bed and then the trampoline exerts an external torque which changes their angular motion.
Why do you think a diver may want to increase their moment of inertia just before they enter the water?
The diver needs to control their entry into the water so they need to reduce the rate of spin. Increaseing their moment of inertia will achieve this as they sprread thier body out away from the axis of rotation.
Explain Newton’s first law of motion in relation to a dancer spinning?
Newton’s 1st law states taht a body will continue to turn about its axis of rotation with constant angular momentum unless an external force is exerted upon it. Therfore the dancer will conti ue to spin with constant angular moentum unless an external force acts on her.
How does a gymnast alter her speed of rotation by changing her body shape?
During rotations angular momentum remains constant. Angular Momentum = moment of inertia x angular velocity. Angular momentum is the quantity of rotations. Moment of inertia is the distribution of mass around the axis. Angular Velocity= speed of rotation. Change in momentum of inertia leads to change in angular velocity/spin of rotation. Moment of interia and angular velocity are inversley proportional. Bring arms/legs closer to axis of rotation leads to increase in angular velocity/speed of rotation. Arms and legs further from axis of rotation leads to a decrease in angular velocity/speed of spin.
Name the three different axes that the body rotates in when angular motion takes place and give a sporting example of each.
Transverse axis - runs from side to side splitting your body top and bottom - somersault in gymnastics
Sagittal axis - runs from front to back - Cartwheel
Longitudinal axis - runs from top to bottom - multiple spin in ice skating.
Define Newton’s 1st Law of Angular motion
A rotating body will continue to turn about its axis rotation with constant angular motmentum unless an external rotational force (torque) is exerted upon it.
ie As an ice skater is 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 which chnages their state of angular momentum.
Define Newton’s 2nd Law of Angular motion
The rate of change angular momentum of a body is proportional to the force (torque) causing it and the change takes place in the direction in which the force (torque) acts. ie the greater the torque exerted the faster the rotation will be.
Define Newtons 3rd Law of Nagular Motion
When a force(torque) is applied by one body to another, the second body will exert an equal and opposite force(torque) on the other body. ie as a goal keeper tips a ball over the bar, they throw their arms up (eccentric action force on the body), which causes the lower part of their legs to go back (reaction force)
What is angular displacement and what is it measured in
The smallest change in angle between the start and finish point of rotation. Measured in Radians and degrees.
Define Moment of Iertia and what does it depend on?
Moment o fInteria is the resistance of a body to angular motion (rotation). Moment of Interia depends upon the mass of the body and the distribution of the mass around the axis.
