Lecture 10: Torque and Rotation

Question 1

Newton’s 2nd Law

Answer 1

When a force is applied to an object, it accelerates in a STRAIGHT line

Force must be applied at the CENTRE OF MASS

Question 2

What happens if force is not applied at the centre of mass?

Answer 2

The body rotates

Question 3

Torque

Answer 3

Aka moment of force

Torque = Force x perpendicular distance

Question 4

Lever arm

Answer 4

Aka moment arm

Distance associated with torque

Only important at RIGHT ANGLES to line of action

Question 5

Torque about a joint

Answer 5

If the object is a body segment that is attached via a joint, then the rotation and torque act about that joint

Question 6

Angular acceleration equation

Answer 6

F = I x a

I = moment of inertia (rotational mass)
a = angular acceleration

Question 7

What 4 characteristics does torque have?

Answer 7

Torque is a vector, so it has:

1. a direction
2. magnitude
3. a point of application (centre of jt)
4. line of action (along axis of rotation)

Question 8

Right hand rule

Answer 8

Thumb up = counterclockwise direction (+)

Thumb down = clockwise direction (-)

Question 9

Torque and angle

Answer 9

Pulling at an angle other than a right angle, REDUCES the amount of torque

Question 10

Torque and centre of mass

Answer 10

Overall centre of mass is the position on the body where the torques created all balance

Question 11

Balancing forces and torques

Answer 11

Balance = no rotation based on TORQUES not forces

Unbalanced torques = rotation

Changing the position of weights will change the torque b/c distance changes

Question 12

Why are knee pushups easier?

Answer 12

It shortens the lever arm for bodyweight, so it produces less torque around the axis

Less torque = less force required from arms