Biomechanical Movement: Angular Motion

Question 1

What is angular motion?

Answer 1

• Refers to rotation
• Rotation = movement around fixed point/axis
• It can involve the whole body or just a limb.
• Angular motion occurs when a force is applied outside the centre of mass
• An off centre force is referred to as an eccentric force

Question 2

What is the transverse axis?

Answer 2

• Runs from side to side across the body
• E.g. sommersault rotates a body in a transverse axis

Question 3

What is the sagittal axis?

Answer 3

• Runs from front to back
• E.g. cartwheel rotates around the sagittal axis

Question 4

What is the longitudinal axis?

Answer 4

• Runs from top to bottom
• a multiple spin in ice skating rotates in a longitudinal axis

Question 5

What is moment of force/torque?

Answer 5

• Angualr motion occurs as a result of torque, often called moment of force
• Torque is the turning force
• It causes an object to turn about its axis of rotation and is dependent on two things:
  …Size-force applied: the greater the ize of the force the greater the torque
  …Perpendicular distance: amplification of the same force further away from the axis will increase torque

Question 6

Calculating moment of force/torque

Answer 6

Moment of force/torque (Nm) = Force (N) x Perpendicular distance from the fulcrum (m)
- The MOF can either be an effort or resistance arm
- Resistance arm: shortest perpendicular distance between fulcrum and resistance
- Effort arm: shortest perpendicular distance between fulcrum and effort

Question 7

What are the principles of moments?

Answer 7

• For a body to be in equilibrium the sum of the clockwise moments is equal to the sum of anticlockwise moments aboutt he fulcrum
• For equilibrium to be achieved the resistance arm must equal the effort arm
• Clockwise = anti clockwise

Question 8

What is Newton’s first law of angular motion?

Answer 8

• “Every body continues in its state of rest or will turn about its axis of rotation unless compelled to change that state by an external rotiational force (torque) acting upon it.”

Question 9

What is Newton’s second law of angular motion?

Answer 9

• The rate of change of angular momentum (acceleration) of a body is proportional to the force (torque) causing it and the change that takes place in the direction which the force (torque) acts.

Question 10

What is Newton’s third law of angular motion?

Answer 10

• “When a force (torque) is applied by one body to another, the second body will exert an equal and opposite force (torqu) on the other body.”

Question 11

What is angular displacement?

Answer 11

• Smallest change in an angle between the starting and finishing point
• Measured in degrees or radians
• 1 radian = 57.3 degrees

Question 12

What is angular velocity?

Answer 12

• Rotational speed of an object and the axis about which the object is rotating
• It’s a vector
• Angular velocity (rads/s2) = change in angular velocity (rads/s)/time taken (s)

Question 13

What is moment of inertia?

Answer 13

• The resistance of a body to change its state of motion when rotating
• Factors affecting it:
  …Mass of an object, the greater the mass the greater the resistance to change, therefore the greater the moment of inertia.
  …Distribution of mass from axis, the further the mass from axis, the bigger the moment of inertia and harder to stop/start movement
• If momentum of inertia is low, angular velocity is high
• If momentum of inertia is high, angular velocity is low

Question 14

What is angular momentum and what is the formula for it?

Answer 14

• Angular momentum = angular velocity x momen of inertia
• Angular momentum is conserved son if momentum is conserved, moment of inertia increases, angular velocity decreases and vice versa. (they are inversely proportional)
• A body will keep spinning/rotating unless forces act upon it
• A body is unlikely to lose mass during movement, but change its distribution or distance from the axis of rotation