4.2 Moments Flashcards
What is a moment
the turning effect of a force
When do moments occur
when forces cause objects to rotate about a pivot
What is the moment of a force given by?
Moment = force x Perpendicular distance from the pivot
What’s the SI unit for a moment
Nm
What is the principle of moments?
for a system to be in equilibrium, the sum of clockwise moments about a point must be equal to the sum of the anticlockwise moments
What is a couple?
a pair of equal and opposite coplanar forces that acts to produce a rotation only
A couple consists of a pair of forces that are:
- equal in magnitude
- opposite in direction
- perpendicular to the distance between them
What is the moment of a couple equal to?
- force c perpendicular distance between the lines of action of the forces
What is the centre of mass of an object?
the point at which the weight of the object may be considered to act
What is the point of symmetry?
- on symmetrical objected with uniform density it is where the centre of mass is located
Where does the centre of mass lie in a stable object
above the base
What is the effect on stability and centre of mass on a wider based object?
- lower centre of mass
- more stable
What is the effect on stability and centre of mass on a narrower based object?
- higher centre of mass
- object more likely to topple over if pushed
What happens to the centre of mass of an object when in space?
- in a uniform gravitational field, the centre of gravity is identical to the centre of mass
- the centre of mass doesn’t depend on the gravitational field
- the centre of gravity does depend on the gravitational field
- when an object is in space the centre of gravity will be more towards the object with the larger gravitational field
