FORCES
V. Ryan © 2002 - 2023

A Static Load : A good example of this is a person seen below, on the left. The person is stood still, he is not moving. The force downwards is STATIC (sometimes called a static load). The load changes to a Dynamic Load when the person begins to move / walk.

INTERNAL RESISTANCE

Internal Resistance : The person in the diagram below, is sat on the mono-bicycle and the air filled tyre is under great pressure. The air pressure inside it pushes back against his weight.

TENSION

Tension : The rope is in “tension” when the two people pull on it. This stretching puts the rope in tension.

COMPRESSION

Compression : The weight lifter finds that his body is compressed by the weights he is holding above his head.

SHEAR FORCE

Shear Force : A good example of shear force is seen with tinsnips and aviation shears (see below). The two handles put force in different directions on the pins that holds the parts together. The force applied to the pins is called shear force.

Another example of shear force:

The number of heavy books ‘piled’ on the shelf, puts pressure on the screws holding the metal bracket to the wall. There is a downward force due to the weight of the books and an opposite force due to the resistance of the wall. This is eventually too much for the screws and their heads ‘shear’ away. The shelf and books fall to the floor.

TORSION

Torsion : The plastic ruler is twisted between both hands. The ruler is said to be in a state of torsion.

When steel is heated to ‘red’ heat, it can be twisted. This creates ‘torsion’ in the steel, a twisting force.