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Name: Brittany
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 1999 


Question:
If you lift a 10lb weight it is considerd doing work, but if you walk a mile with that same weight is it considerd the same type of work? If so, what is the difference between the two?


Replies:
Brittany -

Work is force times distance. It makes no difference in what direction. However, if you lift the object farther above the ground, you have added potential energy (energy of position). If you move the object horizontally, you have still done work, but have added no potential energy.

In the case of lifting the object, because you have stored energy (defined as the ability to do work) you could use it to do work. Just let it go and it will fall. Force times distance...

The energy of position is sometimes called GPE - gravitational potential energy. This differentiates it from potential energy such as chemical potential energy.

work = force times distance

joules = newtons times meters (at least in the metric system)

Do you know what a "slug" is? It is a unit of measure you might want to look up.

Larry Krengel


It's not the same. In the first case, you're moving something against a constant opposing force. The work done is the force you're exerting multiplied by the distance the weight moves while you're exerting the force.

In the second case the only work done is in getting the weight from a standstill to walking speed (I'll assume you're walking in a straight line at constant speed -- i.e., no accelerations). Ideally, once you have the weight moving you just let it coast. It feels like work to you, because muscles use energy just to maintain tension, but the work is not being done on the weight.

Tim Mooney



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