6.3- THE PRINCIPLE OF MOMENTS Flashcards
Whenever you use a lever/spanner, what do you use to turn an object about a pivot?
force
When a force is applied to a spanner, what does the effect of the force depend on?
how far it’s applied from the wheel axle
How is the amount of force needed affected as the spanner is longer?
less force needed
What happens if the spanner is too long?
spanner could snap if too much force applies to it
What is the moment of a force about any point defined as?
force * perpendicular distance from line of action of force to point
What is the unit of the moment of a force?
newton metre (Nm)
How is the moment affected when the distance is increased?
moment increased
What is an object that is not a point object referred to as?
body
How does a body turn?
force applied to it anywhere other than through its centre of mass
What does it mean if a body is acted on by more than one force and it’s in equilibrium?
turning effects of forces must balance out
What is the principle of moments?
sum of clockwise moment = sum of anticlockwise moment
What is the centre of mass of a body?
point through which a single force on the body has no turning effect
In effect, what is the centre of mass?
point where we consider weight of body to act when studying effect of forces on body
How to test the centre of mass with a ruler?
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
How to test the centre of mass of a triangular card?
suspend piece of card on clamp stand
draw pencil lines along plumb line
centre of mass is where lines drawn on card cross
How do you calculate the weight of a metre rule?
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
