Angular motion Flashcards
angular motion
refers to rotation and involves movement around a fixed point or axis.
occurs when a force is applied outside the centre of mass
occurs as a result of a torque
torque
the rotational consequence of a force
causes an object to turn about its axis of rotation
increasing size of force increases torque
applying the force further away from the axis of rotation also increases torque
moment of force or torque= force x perpendicular distance from the fulcrum
newtons first law
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.
an ice skater spinning in the air will continue to spin until they land on the ice when an external force (torque) is exerted from the ice on their skates which changes their state of angular momentum
newtons second law
the 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 in which the force (torque) acts
the greater the torque exerted, the faster the rotation will be
newtons third law
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
as a goal keeper tips the ball over the bar, they throw their arms up (eccentric action force on a body), which causes the lower part of their legs to go back (reaction force)
angular displacement
the smallest change in angle between the start and finish point of a rotation
measures in degrees and radians
1 radian = 57.3 degrees
angular velocity
the rate of change of angular displacement
= angular displacement/ time taken
angular acceleration
the rate of change of angular velocity
= change in angular velocity/ time taken
moment of inertia
resistance of a body to angular motion
depends on the mass of an object and the distribution of mass around the axis
the greater the mass, the greater the moment of inertia
increasing the distance of the distribution of mass from the axis of rotation will increase the moment of inertia
angular momentum
the quantity of rotation a body possesses
= moment of inertia x angular velocity
directly proportional
in moment of inertia increases, angular velocity decreases and vise versa
conserved quantity- stays constant unless an external torque is acted upon it (newtons first law)
When a figure skater performs a spin, ice is a friction free surface so there is no resistance to movement. Only the figure skater can manipulate the moment of inertia to increase or decrease the speed of the 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 is low. When the figure skate up brings their arms and legs back in line with the rest of the body, the decrease of these body parts to the axis of rotation decreases significantly. This reduces the moment of an action which intern increases the angular velocity and the skater spins very quickly.
