Chapter 4

Question 1

The moment of a force

Answer 1

Is the turning effect of a force

• moments occur when forced cause objects to rotate about some pivot
• the size of the moment depends on: size of force. distance between force and pivot
• moment = force x perpendicular distance from the pivot

Question 2

Moments units

Answer 2

Newton centimeter or newton meters

Question 3

Calculating moments

Answer 3

Total clockwise = total anti clockwise moment

Question 4

In equilibrium,

Answer 4

Object keeps doing what it’s doing without any change

• if object is moving it will continue to move, if stationery it will stay stationery, object will not start or stop turning
• the conditions require two things: the forces on object must be balanced, sum of clockwise must be = to anti clockwise (principle of moments)

Question 5

stability and centre of mass

Answer 5

• the centre of mass of an object is the point through which the weight of that an object acts
• an object is stable when its centre of mass lies above its base -if centre of mass does not lie above its base, it will topple over. Most stable objects have a low centre of mass and wider base

Question 6

-finding centre of mass

Answer 6

1. symmetrical object of uniform density (point located at the point of symmetry)
2. an irregular shape: when an object is suspended from a point, an object will always settle that its centre of mass comes to rest below pivoting point

Question 7

experiment to find centre of mass of an irregular shape

Answer 7

-suspended from a pivot and allowed to settle
-a plumb line (lead weight) is the held next to the pivot and a pencil is used to draw a vertical line from the pivot (centre of mass is somewhere on this line)
-the process is then repeated suspending the shape from two different points
(centre of mass is located at point where all three lines collide)