Question

A person was using a spanner to loosen a tight nut.Their mass was 50kg the spanner was 0.5m long i) what is the persons weight?

Answer 1

Answer:

Explanation:

 

An introduction to moments and mechanical forces of rotation

Forces can cause an object to rotate and the turning effect of the force is called a moment.

If a resultant force acts on an object about a fixed turning point (the pivot) it will cause the object to rotate e.g. turning a nut with a spanner, applying a screwdriver, opening a door fixed on hinges. The pivot might also be called the fulcrum.

The rotational or turning effect, the moment, has a magnitude easily calculated from the formula:

M = F x d, where M = the moment of a force (Nm), F = force applied (N)

and d (m) is the perpendicular distance from the pivot point to the line of action of the force.

The perpendicular distance d is the shortest distance between the pivot point and the line of action of the force.

You get the maximum moment by pushing/pulling the spanner at a right angle to the line (d) between the pivot point and the line of action where the force is applied.

Screwing or unscrewing a nut on a bolt

This is illustrated by the simple diagram of a spanner above. The turning force is F x d.

The pivot point is the central axis of the bolt on which the nut is being turned by the spanner.

To tighten or loosen the nut you apply a force, to best advantage, at 90o to the spanner itself.

Applying the force at any other angle less than 90o reduces d and so reduces the effective moment of the force.

You determine the force F by how hard you push/pull the end of the spanner, but d is a fixed distance for give spanner.

This is one of many situations where you are applying a force to increase the effect of your hand muscles.

The size of the moment increases with increase in distance d or applied force F.

The longer the spanner, the greater is d, hence the greater the turning force generated - the greater the mechanical advantage of the lever system.

 

More on the physics of unscrewing a tight nut!

Relative comments on the three 'moment' situations A to C

Situation A

With the longer spanner, and applying the force perpendicular (at 90o) to the line from the point of applying the force to the pivot point (centre of the nut or bolt), you generate the maximum moment (F x d).

The perpendicular distance d, is the shortest distance between the pivot and the line of action of the force

Situation B

If you apply the force at any other angle than at 90o to the perpendicular distance line (d), d will always be shorter and hence a smaller moment is generated by applying the same force as in situation A.

Situation C

With the shorter spanner, despite applying the force at 90o (perpendicular), d is smaller and you cannot generate as large a moment as in situation A.