moment for Alevels students.

1. Turning effect of forces / Moment
For Alevels
By Aliza Ansari…

2. Moment
 It is a product of force and perpendicular
distance between the line of action of
force and the pivot.
 It is a vector quantity .
 Its direction is either “Clockwise” or
“Anti-Clockwise”.
 Its unit is Newton metre (Nm).
 Its base unit is kilogram metre square per
second square (kgm^2s^-2).

3. Centre Of Gravity :
 The point where the whole weight of the
body is assumed to act.
 For a regular shaped object the centre of
gravity is acting at the “geometrical centre”
of the object.
 For the irregular shaped object, the centre of
the gravity can be determined by balancing it
on a sharp or knife edge.
 The “plumb line” method is used to
determine the centre of gravity of a plain
lamina .

5. What is plumb line method ??
 Make 3 holes at the corners of lamina ,
suspend the lamina through each hole and
then draw a vertical line using a plumb
line for each hole . The point of
intersection of the 3 lines would be “the
centre of gravity”.

6. Principle of
moments

7. Principle of moments :
 Sum of clockwise moments about a point
is equal to sum of anti-clockwise
moments about the same point.
 The sum of moments about the point is
ZERO.

8. Equilibrium / Conditions of Equilibrium
two conditions for a body to be in
equilibrium.
1.Sum of all the forces acting on a body
is zero.
2.Sum of the moments about a point is
zero.

9. Couple
A couple is a pair of forces having same
magnitude but opposite in direction and
having different line of action.

10. Torque of a couple :
 A couple producing a turning effect
known as “Torque of a couple”.
 Torque of a couple is a product of
magnitude of one of the forces and the
perpendicular distances between the
forces.