Turning effects of motion
● If something is balanced the moments are equal and opposite
● The size of a moment depends on
○ The size of the force
○ The distance between the force and the pivot
● Moment of force
○ The turning effect of force is called the moment of force
or it is the product of force and perpendicular distance
○ Moment = force x perpendicular distance
○ S.I unit of moment is Nm (newton metre)
● Pivot
○ Centre point/ fixed point at which the object will turn
● Turning effect of force is also known as torque or moment
● Principle of moment
○ For an object to be in equilibrium, the sum of all clockwise moments about a pivot is equal
to the sum of anticlockwise moments about the same pivot
○ There must be no resultant force acting on it
● Centre of mass
○ It is a point in space where all the mass of an object can be thought to act
● Method to find centre of mass of an irregular object
○ Suspend the shape
○ Draw a plumb line
○ Suspend the shape from another location
○ Mark the line again
○ THe intersection of the 2 lines is the centre of mass
● Centre of gravity/ stability
○ Point at which the entire weight of an object appears to act
● How to get more stability
○ More base width of the object, the more stable
○ More mass of body, the more stable
○ Lower the centre of gravity, higher the stability
● Centre of mass of plane lamina
○ Make 3 holes around edge of lamina
○ Fix pin horizontally in the clamp
○ Using one hole, hang the lamina from the pin, it should be able to turn freely
○ Hang string from pin, make 2 points on the lamina along the length of string
○ Repeat steps 3 and 4 for the other holes
○ Lay the lamina, using a ruler, draw lines joining each pair of points, where the lines cross is
the centre of mass of the lamina
