B Non-physicist needs your help torquing a nut!

[AlanSta]

TL;DR Summary

Zero understanding in physics, need to torque a nut (500Nm) by applying my weight (62.5kg) at a certain distance of the wrench (81.5cm?). And I need you to correct me.

Hello, as you can tell by the title I don’t work with anything physics related nor do I study it. I’m trying to figure out if I can torque a nut without a torque wrench, and I have ZERO understanding in physics.

And I need your help to tell me that I’m wrong.

I want to try to torque the nut by applying my weight on a wrench at a certain distance from the socket.

From what I’ve read the torque calculation consists of: Distance (r), Force (F) and Torque (T). And that force is Weight x Acceleration.

First the Force.
I would be standing on the wrench so it would be acceleration of gravity which is 9.81m/s2, and my weight with clothes aprox. 62.5kg.

62.5kg x 9.81m/s2 = 613N

The torque that I want to achieve is 500Nm, I used a Torque Calculator for this one, since I don’t know the equation and this is what I got.

Distance (r) 81.5cm
Force (F) 613N
Torque (T) 500Nm

Now if I’m somewhat close to correct, then if I apply my weight 81.5 cm from the center of the socket then I will achieve torque of 500Nm?

How wrong am I?

 

[Baluncore]

Welcome to PF.

How wrong am I?

You are correct.
500 / ( 62.5 * 9.81 ) = 0.815 m

 

[Orodruin]

TL;DR Summary: Zero understanding in physics, need to torque a nut (500Nm) by applying my weight (62.5kg) at a certain distance of the wrench (81.5cm?). And I need you to correct me.

since I don’t know the equation

The equation is rather simple:
$$
T = Fd
$$
where $T$ is torque, $F$ force, and $d$ the lever arm.

 

[berkeman]

500Nm

That must be a pretty big nut! What does it go on?

 

[Steve4Physics]

Hi @AlanSta. Welcome to PF!

In addition to what's already been said, it may be worth noting that the wrench needs to be horizontal - or reasonably near horizontal - when you do it.

That's because, for the calculation to be correct, the force (your weight acting vertically downwards) needs to be perpendicular to the wrench.

If the force and wrench aren't perpendicular, the calculation is slightly more complicated.

Edit - typo's

 

[Orodruin]

If the force and wrench aren't perpendicular, the calculation is slightly more complicated.

It doesn't need to be though, as long as one remembers that it is the horizontal distance that is the lever arm. If the wrench is too long, simply turn it until the horizontal projection has the required length.

 

[Steve4Physics]

It doesn't need to be though, as long as one remembers that it is the horizontal distance that is the lever arm. If the wrench is too long, simply turn it until the horizontal projection has the required length.

Good point. But there could be health and safety implications if trying to do this (perhaps without assistance) whilst balancing on (or hanging from) a long non-horizontal wrench!

Edit: I originally typed 'wench' before correcting it to 'wrench'. Which I found amusing!

 

[Lnewqban]

Welcome, Alan!

Consider that while you stand on the wrench, the end or socket in contact with the nut will tend to slip out of position.
More, the more your force is off the same vertical plane of the nut.
Normally, we hold the socket in place with one hand and apply force with the other.

Also, jumping on the wrench will greatly increase the torque reaching the nut.

 

[sophiecentaur]

In many cases, the torque is specified with dry or oiled threads and always, I'd say, everything should be corrosion free. But that may be telling my grandmother how to suck eggs. But, like at sea, it's better to be told twice than not at all.

 

[Herman Trivilino]

Also, jumping on the wrench will greatly increase the torque reaching the nut.

I'll never forget learning this lesson. My friend and I couldn't for the life of us get the lug nuts loose on his VW. His neighbor came from across the street and performed this magic trick for us.