1.4.1 - 1.4.3 - Moments

Question 1

What else can forces cause objects to do?

Answer 1

As well as causing objects to speed up, slow down, change direction and deform, forces can also cause objects to rotate
An example of a rotation caused by a force is on one side of a pivot (a fixed point that the object can rotate around)
This rotation can be clockwise or anticlockwise

Question 2

What is a moment defined as?

Answer 2

The turning effect of a force about a pivot

Question 3

What is the eq. for calculating the size of a moment?

Answer 3

Moment = Force x Perpendicular distance of the force to pivot in meters

M = F X D

Question 4

How does a door handle create a moment?

Answer 4

This is why, for example, the door handle is placed on the opposite side to the hinge
This means for a given force, the perpendicular distance from the pivot (the hinge) is larger
This creates a larger moment (turning effect) to make it easier to open the door
Opening a door with a handle close to the pivot would be much harder, and would require a lot more force

Question 5

What is the principle of moments?

Answer 5

If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot

The forces should be perpendicular to the distance from the pivot
For example, on a horizontal beam, the forces which will cause a moment are those directed upwards or downwards

Question 6

How can moments be linking to supporting a beam?

Answer 6

A light beam is one that can be treated as though it has no mass
The supports, therefore, must supply upwards forces that balance the weight of any object placed on the beam
As the mass in the above diagram is moved from the left-hand side to the right-hand side of the beam, force F1 will decrease and force F2 will increase

Question 7

What is the centre of gravity?

Answer 7

The point through which the weight of an object acts

For a symmetrical object of uniform density, the centre of gravity is located at the point of symmetry
The centre of gravity of an irregular object can be found by locating its balance point
A broomstick has a centre of gravity slightly closer to the head of the broom since there is more mass located there