The equation for moment M
M = Fd
Moment of a torque
It is the product of the force and the perpendicular distance of the force from the pivot
Torque of a couple
It is the product of a magnitude of one force and the perpendicular distance between two forces
The equation for torque T
T = Fd
Centre of gravity
It is the point at which the whole weight of the body is considered to act
Principle of moment
The sum of the clockwise moments about a point equals the sum of the anticlockwise moments about the same point
2 conditions for a body to be in equilibrium
- Resultant force is zero
- Resultant moment / torque is zero OR
sum of clockwise moments = sum of anticlockwise moments
Describe how to draw a vector triangle to represent forces in equilibrium. Add a confirmation.
- Each force is represented by an arrow - in magnitude and direction
- The arrows are joined head to tail
(Confirmation: If the triangle is ‘closed’, then the forces are in equilibrium)
Why a weight couldn’t be supported by strings that are horizontal
- The forces in strings would be horizontal
2. So, there’s no vertical force to support the weight
A card swings on a rod. List 2 forces, other than weight and air resistance, that act on the card during the time it is swinging
- Normal reaction force at the rod
2. Friction force at the rod
State the position in which the cards come to rest. Explain.
The card comes to rest with the weight acting through the rod and allows the centre of gravity to be vertically below the rod.
