11.2 Angular Motion Flashcards
What is angular motion?
- Refers to rotation and involves movement around a fixed point or axis
When does angular motion occur?
- Occurs when a force is applied outside the centre of mass
What is newtons 1st law?
- Resistance an object has to change in its state of motion
- An object will stay in place till a force is applied to move it
e.g. at the start of a floor routine a gymnast remains still until a force is applied in motion
What is inertia?
- The bodies resistance to change in motion & is related to mass
- If you want to get an object with a large mass moving you have to apply more force in comparason to a tiny object
What is newtons 2nd law?
- The size and direction of the force applied, determines the size and direction of the acceleration given to the object
e.g. to provide acceleration at the start of a race an athlete has to apply a large force internally through the gluteal, gastronemius & quadricpets to drive forward
How do you calculate force?
Force= Mass X Acceleration
What is Newtons 3rd Law?
- For every action there is an equal and opposite force
- Law describes what happens when two bodies (or objects) exert force on one another
- Action & reaction are equal & opposite & always occur in pairs
A&R force e.g swimmer pushes water in backwards direction
Water will then exert force on swimmer
What is the ground reaction force?
- GRF= The equal and opposite force exerted on a performer who applied a muscular force on the ground
- This force is exerted on the ground by the body contact with it
What is the formula for angular velocity?
Angular displacement/ Time taken
What is the formula for angular acceleration?
Change in angular velocity/ Time taken
What is your centre of mass?
- The point of balance
- Centre of mass is always moving depending on your movements
What is the line of gravity?
- The line extending vertically downwards from the centre of mass
Why is stability so important?
- A stable body position will enable an athlete to resist motion
- You cannot perform to your best if you are unbalanced
What is the stability of an athlete affected by?
- The height of the centre of mass- lowering COM will increase stability
- The position of the athletes line of gravity- should be central over base support to increase stability
- The size of the athletes area of support- larger base support becomes- more stability increases
- Mass- Often the greater the mass the more stability there is because of increased inertia
What factors affect the centre of mass?
- The mass of the body or object
- The size of the base of support- The lower the more stable - but if your mass moves too near base of support you will over balance
- The number of points in contact with the surface
- The closer the line of gravity is to the base of support- the more stable the body
What is angular displacement?
- Angular displacement is the smallest change in angle from the starting point to the finishing point
- Angular displacement & angular velocity are both measured in radians: 1 radian=57.3 degrees
What is angular velocity?
- The rate of change of angular displacement
- Refers to the rotational speed of an object & the axis about which the object is rotating
- This is a vector quantitiy as it refrences direction
How do you work out angular velocity?
- Angular displacement (rad)/ Time taken (s)
What is angular acceleration?
- The rate of change of angular velocity
How do you calculate angular acceleration?
- Change in angular velocity (rad/s) / Time taken (s)
What is the moment of inerta?
- Resistance of a body to angular motion
- Can be applied to the start of rotation when a body will resist angular motion ; but once the rotation occurs, the body will want to continue to turn about its axis of rotation
moment of inertia depends upon the mass of the body & the distribution of mass aorund the axis
How does the mass of the body/object got to do with the moment of inertia?
- The greater the mass, the greater resistance to change & therefore the greater the moment of inertia
e.g. a ten-pin bowling ball is more difficult to roll along the ground than a football, but once it starts rolling, it is more difficult to stop than the lighter ball
What has the distribution of mass from the axis of rotation got to do with the moment of inertia?
- The closer the mass is to the axis of rotation, the easier it is to turn, because the moment of inertia is low
- Increasing the distance of the distribution of mass from the axis of rotation will increase the moment of inertia
e.g. performing a somersualt in a pike has a higher momentum of inertia than a tucked somersault because in the pike position the distribution of the divers mass is further away from their axis of rotation. AAR- the piked somersault is more difficult to perform than a tucked somersault
What is meant by ‘angular momentum’.
- The quantity of rotation a body possesses (spin)
- It involves ab object or body in motion around an axis
What is the formula for angular momentum?
- Moment of inertia X Angular velocity
How does angular momentum actually occur?
- Angular momentum is a conserved quantity- it stays constant unless an external torque (force) acts upon it (Newtons 1st law)
e.g. angular momentum can be highlighted when a figure skater performs a multiple spin, turning on a longitudinal (verticle) axis- ice is a friction free surface so there is no resistance to movement.- only figure skater therefore can manipulate their movemet by stretching their arms & legs in and out- which increases their distance from the axis of rotation, resulting in large moment of intertia
