I have been given the breaking strain of rope in Newtons and that of wire in tonnes/kilogrammes. What is the formula or ratio I need to know in order to compare them in like units?
Remember the basic formula, F=MA? F is force, measured in Newtons. M is mass, measured in kilograms. A is acceleration, measured in m s[sup]-2[/sup] (meters per second per second). I’d guess the mass is hanging from the rope, and both are stationary. So the accelration is just the gravitational acceleration, i.e. 9.8 m s[sup]-2[/sup].
But if everything is at rest, why do we use acceleration? Because Einstein told us that gravity is the same thing as acceleration. Or to think of it another way, if the mass wasn’t pulled up with anything, it would fall at 9.8 m s[sup]-2[/sup]. So to suspend the mass and prevent it from falling down, the rope must counteract this 9.8 m s[sup]-2[/sup] acceleration.
[nitpick]I thought Isaac Newton was the one who formulated the concept of gravitational acceleration, not Einstein. F = ma is Newton’s second law of motion, after all.[/nitpick]
Regarding the OP, the Newton is the SI unit of force. The pound is the British unit of force. One pound is equivalent to 4.45 Newtons. So one ton would be equivalent to 8900 Newtons, assuming you define 1 ton = 2000 pounds. If you’re talking about a metric ton (1 ton = 1000 kg), then 1 ton = 9800 Newtons.
I think he was. Usually the spelling tonne means the metric ton.
I think it is inaccurate to give the breaking strain of anything in units of mass as opposed to force. The same piece of wire, if used to suspend something on the moon, would support a lot more mass but exactly the same force. To give the breaking strain in mass is to foolishly assume that the wire/rope/whatever will always be used in Earth normal gravity. That is a bad assumption to make for a guy who gets around like myself.
>> I think it is inaccurate to give the breaking strain of anything in units of mass as opposed to force.
You are (of course) technically right, but customarily wrong. Units of mass are constantly used as force and everybody knows what is meant. When some nitpick like yourself points out is is technically incorrect, the rest, just to shut him up, will say ok, make that Kgf (meaning kg of force which is the force needed to accelerate a mass of 1 KG at 1g).
Although unit conversions are one of my favorite things to do and talk about (seriously!), please, nobody bring up the lowly slug…
14.59 kg. Heh.