# Work

Discussion in 'Physics & Math' started by Arcotik, Nov 15, 2007.

1. ### ArcotikRegistered Member

Messages:
30
Ok, W = Fd. Question: is there work when someone lifts and object upwards with a y-displacement but no x-displacement? What about when they let it come down?

The book I have is confusing. Help?

to hide all adverts.
3. ### draqonBannedBanned

Messages:
35,006

to hide all adverts.
5. ### ArcotikRegistered Member

Messages:
30
I didn't care too much for the link. I don't know...I'm in a weird bit of states right now. Thanks all.

to hide all adverts.
7. ### James RJust this guy, you know?Staff Member

Messages:
31,272
The equation you have given applies to a constant force F in the same direction as the displacement d.

The force of gravity on an object is F=mg, and it acts vertically downwards. If you lift an object distance h in the vertical direction, the work done by gravity is

W = Fd = -mgh

where the negative sign comes because the displacement (upwards) is in the opposite direction to the force (downwards).

When you drop an object from height h, the work down by gravity as it falls to the ground is

W = mgh.