6.3- THE PRINCIPLE OF MOMENTS

Question 1

Whenever you use a lever/spanner, what do you use to turn an object about a pivot?

Answer 1

force

Question 2

When a force is applied to a spanner, what does the effect of the force depend on?

Answer 2

how far it’s applied from the wheel axle

Question 3

How is the amount of force needed affected as the spanner is longer?

Answer 3

less force needed

Question 4

What happens if the spanner is too long?

Answer 4

spanner could snap if too much force applies to it

Question 5

What is the moment of a force about any point defined as?

Answer 5

force * perpendicular distance from line of action of force to point

Question 6

What is the unit of the moment of a force?

Answer 6

newton metre (Nm)

Question 7

How is the moment affected when the distance is increased?

Answer 7

moment increased

Question 8

What is an object that is not a point object referred to as?

Answer 8

body

Question 9

How does a body turn?

Answer 9

force applied to it anywhere other than through its centre of mass

Question 10

What does it mean if a body is acted on by more than one force and it’s in equilibrium?

Answer 10

turning effects of forces must balance out

Question 11

What is the principle of moments?

Answer 11

sum of clockwise moment = sum of anticlockwise moment

Question 12

What is the centre of mass of a body?

Answer 12

point through which a single force on the body has no turning effect

Question 13

In effect, what is the centre of mass?

Answer 13

point where we consider weight of body to act when studying effect of forces on body

Question 14

How to test the centre of mass with a ruler?

Answer 14

balance ruler at its centre on end of your finger
centre of mass of ruler directly above point of support
tip ruler too much and it falls as centre of mass no longer above point of support

Question 15

How to test the centre of mass of a triangular card?

Answer 15

suspend piece of card on clamp stand
draw pencil lines along plumb line
centre of mass is where lines drawn on card cross

Question 16

How do you calculate the weight of a metre rule?

Answer 16

locate centre of metre rule by balancing it horizontally on horizontal knife-edge
note position of centre of mass

balance metre rule off-centre on knife-edge, using known weight W1
position of known weight needs to be adjusted gradually until rule exactly horizontal