A friend of mine just asked the following question after hearing Richard Hammond make a comment. She said:
“I think Hammond got it totally wrong when he gave a metaphor for a dragster suddenly swerving and crashing (a ‘moment’) as the difference between using a short-handled, smaller spanner to using a longer-handled, bigger spanner to tighten a bolt (no – in my book, the spanners show a difference in ‘leverage’). It is always recommended that women (yeah, yeah – depending on size and body-building, etc.) use longer-handled spanners, etc., because they give more leverage. Am I wrong, or missing something? Leverage, in my book, has nothing to do with “moments.” Come on e-learning teacher!”
And my reply is as follows (they are both correct by the way, but using different words for the same thing!):
A longer lever (spanner) means you need less force on the end of it to produce the same torque (turning force) at the nut – a person with a shorter spanner would need to apply more force on the spanner than you. This is as you suggest, the law of levers. Torque is arguably the same thing as a Moment which is defined as: “A turning effect produced by a force acting at a distance on an object.” Or perhaps better as: “The magnitude of a turning effect produced by a force acting at a distance, expressed as the product of the force and the distance from its line of action to a given point.”
Force (N) x distance (m) = Torque (Nm or Newton-meters)
However, moments are usually used to describe the way combinations of forces affect something. As long as all the moments on a car cancel each other out for example then it will not start to spin!
If you have a moment to spare – please add a comment! 🙂
PS. Why are we all so worried about Clark’s son at the moment – and who is Clark anyway?
PPS. To all my good friends in the USA a spanner is the proper name for a wrench…