# Thread: How do you calculate Torque from mass?

1. ## How do you calculate Torque from mass?

Simple question that has a probably very complicated answer:

I have a mass I would like to estimate to be a maximum of 500 lbs, and I know it's approximate rate of speed (eyeballing it). I also know the rear axle on which this mass sits is 1" in diameter with about 12" tires. Where I am confused is how I go from X lbs of force, at Y rate of speed, to a torque.

How the heck do I find the torque being applied at the rear axle?

I created a previous thread regarding a weight sled for a truck pull and this is the same project. I need to know how to find the torque so I can select the proper overload clutch. Also if it would help I could probably measure the pulling force it takes to move the sled once I build it and go from there instead of using the actual sled mass.

2. If the load is being carried on the axle/wheels at a constant speed the force required to keep it moving at that constant speed depends on the rolling friction of the bearings and tires.

For instance if the rolling friction is 0.1 it means you have to apply a force of 50lbs to keep your 500lb load moving at a constant speed. You have two 12" diameter tires in contact with the road so each tire contributes 25lbs. The radius of the tire is 6" so that is the lever arm for calculating the torque which is 25lbs * 0.5ft = 12.5lb-ft.

This calculation ignores the fact that the tire compresses slightly under the load so the radius is a bit less than 6".

Your idea of actually measuring the force required to move the load is a good approach because you do not know what the rolling friction is.

3. Torque is a measure of static turning force. vis pound force-foot or newton-meters etc.

Momentum is a vector quantity
mass and velocity p= mv lbs./ feet/ sec etc.
( rotation is a direction with v in radians /sec)
Horse power combines the two. i.e. pound-feet/sec

What you really need to discover a "torque" value is the acceleration + or - that your 500 lb load will experience.
mv^2. .-) Reflect on gravity at 1G (32 ft/sec/sec)