CH5: Turning Effects of Forces Flashcards
define moment
a quantity that measures the turning effect of a force
define moment of a force
the product of the force and the perpendicular distance from the pivot to the line of action of the force.
formula and SI unit of moments
moment = force x perpendicular distance
SI unit: Newton metre (Nm)
what does moment consist of?
anticlockwise moment and clockwise moment
state the principle of moments
the principle of moments states that when a body is in equilibrium, the sum of anticlockwise moments about a pivot is equal to the sum of clockwise moments about the same pivot.
written formula of equation of moments
taking moments about a pivot,
sum of anticlockwise moment = sum of clockwise moment
what affects the amount of force needed to have a turning effect of force?
the perpendicular distance from the pivot to the line of action
define centre of gravity
the centre of gravity of an object is an imaginary point where the entire weight of an object seem to act.
what happens to the centre of gravity when a body is suspended freely?
when a body is freely suspended, the centre of gravity is always directly below or directly above the pivot (or point of suspension).
why does an object not topple when it is slightly titled to the left?
for an object to not topple, the line of action of the weight of the object must be withing the base area of the object. therefore, it does not topple as its centre of gravity (line of action) is still within the base area of the object.
describe how is centre of gravity determined for irregular-shaped objects?
the centre of gravity can be determined using the plumb line experiment.
1. mark and label three holes near the edge of the lamina (flat irregularly shaped material).
2. suspend the lamina freely on a pin until it rests vertically.
3. place a string on the pin in front of the lamina and trace the position of the string.
4. repeat step 2 and 3.
5. the solid lines should intersect at one point which will the centre of gravity.
