Further Physics - Turning Forces

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Turning Forces

Moments

A moment is a turning force.
Moment = force x perpendicular distance from the pivot to where the force is

How can we increase moment?

  • Increasing the amount of force (push harder!)
  • Longer leverage (a really long spanner)Lever (http://www.forteachersforstudents.com.au/Engineers/images/SM_diagram1.jpg) This diagram (^) shows how a lever works. Force or effort is applied to the lever around a pivot or fulcrum. The result is that the load is moved. 
  • This means that moment = force x perpendicular distance
  • Newton metres = newtons x metres#

 Centre of Mass

The centre of mass is the centre of gravity on an object

The point where all the mass of an objected is thought to be concentrated

Suspended Equilibrium (http://gcserevision101.files.wordpress.com/2009/02/suspended-equilibrium.jpg?w=510&h=281)

Suspended Equilbirum. 

The hanging baskets are both suspended. However, when the hanging basket is in equilibrium, ie, balanced - its centre of mass is directly below the suspension point.

When the basket is turned away from its equilibrium position like the basket on the right, if it is released it will return to its equilibrium position. 

In a symmetrical object, the centre of mass is where all the axes of symmetry meet up. 
For example, a rectangle has two axes of symmetry
An equi triangle would have three axes.

Moments in Balance

When a seesaw is balanced, it is an example of the anticlockwise moments and the clockwise moments balancing each other out. 

However, they may not be necessarily sat at the same point on either end of the seesaw. 

Person A may weight less than Person B and sits nearer to the pivot of the see saw. However, this still results in balance. 

W1D1 = W2D2

This means;
For equilibrium the anticlockwise moments about the pivot = the clockwise moments about the pivot. 

This is the Principle of Moments

Example:

Find W1 if;
W2 = 0.4N. D1 = 0.25m and D2 = 0.20m.

Rearrange W1D1 = W2D2

W1 = W2D2/D1
W1 = 4N x 0.2M/0.25M
W1 = 3.2N 

Find how far away John should sit if; 
John (W1) = 450N. Jasmine (W2) = 425N & sits 2M away;

W1D1 = W2D2
450 x D1 = 425 * 2
D1 = 425 * 2…

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