Re: True or False.... Ft/Lbs.

Posted by Rod (NH) on December 03, 2003 at 16:18:51 from (12.148.160.138):

In Reply to: True or False.... Ft/Lbs. posted by Just Curious on December 03, 2003 at 14:03:04:

Hi Just Curious,

Odd name you got there :o). Here's another opinion. There is no valid term as ft/lb. What I think you mean is ft-lb which is an energy term. It represents a force acting THROUGH a distance on an object. Despite common usage, ft-lb is NOT a term that properly designates torque. Torque is a force acting AT a distance on an object not THROUGH a distance. Big difference. To acknowledge that difference, torque is properly termed as lb-ft and not ft-lb.

The samples you provide develop an energy (kinetic energy) of 200 ft-lb and 300 ft-lb respectively. Weight times height. This is not a force. The actual force that is developed when the weight lands depends entirely on the relative stiffness of the weight and whatever the weight lands on. That amount of energy has to be dissipated (usually by deformation of one or both objects) upon landing in order to bring the weight to rest. Extremely high forces can be developed when hard weights land on hard surfaces. A steel cannon ball on a concrete surface for instance. In comparison, the force developed by that same cannon ball when landing on a pile of modelling clay would be much less due to the relative ease of deformation of the clay.

The above is true if one neglects the effects of any change of gravity with height and the resistance of the air. Both are negligeable in the context of your question, I believe.

Rod

Follow Ups:

• Re: Re: True or False.... Ft/Lbs. HTR 17:38:58 12/03/03 (0)
• Re: Re: True or False.... Ft/Lbs. thurlow 16:43:01 12/03/03 (0)

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