angular motion Flashcards
1
Q
angular motion
A
- is a rotation around an axis
- occurs in sport all the time
- refers to rotation and involves moment around a fixed point or axis
- occurs when a force is applied outside the centre of mass
2
Q
eccentric force
A
- an off centre force
- E.G the whole body is sommersault
- E.G the arms of a discuss thrower
- E.G a runner will show angular motion , although running is linear
- there is a significant amount of rotational movemtns on the running action of the arms and legs as they rotate around a joint
3
Q
3 axis
A
- transverse axis - which runs from side to side across the body
- somersault
- sagittal axis - which runs front to back
- cartwheel
- longitudinal axis - which runs top to bottom
- piroutte
4
Q
torque
A
- angular motion occurs as a result of torque
- torque is a turning force
- causes an object to turn about its axis of motiont
- increase the size of the force , torque is increased
- applying the same amount of force further away from the axis of rotation also increase torque
- E.G if you apply a large amount of force next to the hinge of a door , the torque will be less than if you applied the same amount of force to the edge of the door
- this means the perpendicular distance force from the pivotal point (moment arm) will increase the amount of force
5
Q
torque equation
A
- moment of force/torque (Nm) = force (N) x perpendicular distance from the fulcrum (M)
6
Q
newtons first law of motion
angular analogues of newtons laws of motion
A
- a rotating body will continue to turn about its axis of rotation with constant angular momentum unless an external rotational force (torque) is exerted upon it
- E.G an ice skater who has jumped in the ar will carry on spinning until they land on the ice when torque is exterted from the ice on their skates
7
Q
newtons second law of motion
angular analogues of newtons laws of motion
A
- the rate change of angular momentem of a body is proportional to the force (torque) causing it and the change that takes place in the direction in which the force (torque) acts
- E.G the greater the torque exterted on an object, the faster the rotation will be
8
Q
newtons third law of motion
angular analogues of newtons laws of motion
A
- 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
- E.G when you are running and the leg goes forward, your top part of the body will rotate in the opposite direction to balance you out
- when running our arms and legs work opposite to each other to stop us from over rotating
9
Q
angular displacement
quantities used in angular motion
A
- is the smallest change in angle between the starting and finishing points
- is measured in degrees and radians
- 1 radian = 57.3 degrees
- radian is the unit of measurement of angles
10
Q
angular velocity
quantities used in angular motion
A
- refers to the rotational speed of an object and the axis about which the object is rotating
- this is vector quanitity as it reference to direction
- it refers to angilar displacement covered in a certain time
- angular velocity (rad/s) = angular disaplcement (rad) / time take (s)
11
Q
angular velocity equation
quantities used in angular motion
A
- angular velocity (rad/s) = angular disaplcement (rad) / time take (s)
12
Q
angular acceleration
quantities used in angular motion
A
-
this is the rate of change in angular acceleration
* Angular acceleration (rads/s2) = change in angular velocity (rad/s) / time taken (s)
13
Q
angluar acceleration equation
quantities used in angular motion
A
Angular acceleration (rads/s2) = change in angular velocity (rad/s) / time taken (s)
14
Q
moment of inertia
moment of inertia
A
- is the resistance of a body to angular motion (rotation)
- this can be applied to the start of rotation when a body will resit angular motion; but once the rotation occurs, the body will want to continue to turn about its axis of rotation
15
Q
what affects moment of intertia
moment of inertia
A
- mass of the body
- distribution of mass from the axis of rotation
16
Q
mass of the body
moment of inertia - what affects it
A
- the greater the mass , the greater the resitance to change and therefore the greater the moment of intertia
- E.G bowling ball is much more difficult to start rolling than a football, but once it starts rolling, it is more difficult to stop than a football
17
Q
distrubtion of mass from the axis of rotation
moment of inertia - what affects it
A
- the closer the mass is to the axis of rotation , the easier it is to turn , bc the moment of inertia is low
- increasing the distance of the distrubtion of mass from the axis of rotation will increase the moment of intertia
- E.G in gymnastics a tucked somersault is eaasier than a straight sommersault , as the distrubtion of mass is closer to the axis of rotation
18
Q
angular momentum
angular momentum
A
- angular momentum (L) is the quantity of rotaton a body possessed - SPIN
- it invloves a body in motion around an axis , it depends on the moment of inertia (I) and angular velocity (ய)
- angular momentum = moment of inertia (I) x angular velocity (ய)
- these two are inversly proportional; if the moment of intertia increases, angular velocity decreases and vice versa
19
Q
conservation of angular momentum
angular momentum
A
- angular momentum is conserved quantity - it stays constant unless an external torque acts upon it (newtons first law)
- E.G this happens during flight or on ice as there is minimal friction
20
Q
figure skater analgy
angular motion
A
- when a skater spins on the longitudinal axis , they will continue to spin due to no friction from the ice
- the only way the skater can manipulate their moment of intertia is to increaseor decrease their speed of spin
- at the start of the spin , the arms and legs are stretched out
- this increases their distance from the axis of rotation, resulting in a large moment of inertia and a large angular momentum in order to start the spin, so rotation in slow
- the figure skater brings their arms and legs back in line with the rest of the body
- this decreases the distance the body parts are away from the axis of rotation
- which in turn increases their angular velocity and the skater spins very quickly
