3.4.1.2 Moments Flashcards
What is the mass of an object?
The amount of matter in it (?)
What is a moment?
The product of a force and the perpendicular distance from the line of action of the force to the pivot, that causes a turning effect on an object.
What is the formula for moment?
Moment (Nm) = Force (N)* perpendicular distance from the pivot (m)
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 (about the same point)
What is a couple?
A pair of equal and opposite coplanar force that acts to produce a rotation only.
The pair of forces are:
Equal in magnitude, opposite in direction and perpendicular to the distance between them.
They have a resultant force of zero.
What is the formula for couples?
Moment of a couple = force * perpendicular distance between lines of action of forces
What is the centre of mass of an object?
The point at which the weight of the object may be considered to act;
For symmetrical objects with uniform density, the centre of mass is located at the point of symmetry
What is stability?
The position of the centre of mass of an objects affects its stability, an object is stable when its centre of mass lies above its base.
How does the base of an object affect its stability?
The wider the base, the lower its centre of mass and the more stable it is.
The narrower the base, the higher its centre of mas and the object is more likely to topple over if it is pushed
Compare centre of gravity and centre of mass
In a uniform gravitational field, centre of gravity is identical to centre of mass.
Centre of mass does not depend on the gravitational field.
Centre of gravity does depend on the gravitational field (since weight=mg)
