Define the expression of work done by constant force
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Work
Work is done when a force is applied, at least partially, in the direction of the displacement of the object. If that force is constant then the work done by the force is the dot product of the force with the displacement:
W=\vec{F} \bullet \vec{d}.
W=
F
∙
d
.
The net work done on an object (the work of the net force) is equal to the energy added to the object. This is the reason for both the unit of work being the Joule, \text{J}J, and the work-kinetic energy theorem:
W=\Delta K.
W=ΔK.
Anne spends most of her day napping on a futon. In the reference frame of the Earth, what is the work done to Anne by the futon in one hour?
A futon is a couch that can also be folded flat to serve as a bed.
A futon is a couch that can also be folded flat to serve as a bed.
In the reference frame of the Earth, Anne is sitting still, so her displacement is 0 \text{m}m in any amount of time. Hence the work done in one day is
W=\vec{F} \bullet \vec{d} = \vec{F} \bullet \vec{0} = 0 \text{ J}.
W=
F
∙
d
=
F
∙
0
=0 J.
Work is done when a force is applied, at least partially, in the direction of the displacement of the object. If that force is constant then the work done by the force is the dot product of the force with the displacement: W = F ⃗ ∙ d ⃗ .