Question

in order for work to take place ...

Answer 1

In order for work to take place, force must be applied in the direction of motion.

Answer 2

......and motion must occur - in the direction of the force applied!!!

Answer 3

Work is equal to a force applied over a distance. \[W=Fd\]

Answer 4

All the above is not the NECESSARY CONDITION

The necessary condition can be put in the following fashion

A force is said to do work, if it displaces the object (in aNY DIRECTION but 90 degrees).

if the direction makes an acute angle with the applied force, the work done is positive
if the direction makes an obtuse angle, then the work done is negative , and if direction is perpendicular to applied force, then work is said to be zero.!

Answer 5

To elaborate on what @Mashy said, work is the dot product of the force vector and the displacement vectors:\[\large W= \vec F \cdot \vec d=Fd \space cos(\theta)\]From there you can see that if the angle between the force and displacement vectors is 0 degrees, no work is done. If it's acute (ie: in the direction of motion), then positive work is done...if it's obtuse, then negative work is done.

In general terms, work is done ON an object if the calculation above results in a positive value. This is why the first two posters stated that the motion must be in the direction of the displacement.

Answer 6

you can still say a NEGATIVE work is done ON an object, when the angle is obtuse :P.. technically.. so work can be done regardless of what angle.. (except for 90 degrees ofcourse :D)

Answer 7

is this the full condition?

Answer 8

BTW: Small correction in my earlier post...that should have read 90 degrees :)

Answer 9

@Mashy: I guess you could say that. But negative work ON an object is essentially the same as positive work done BY the object.

Answer 10

If you want to argue technicalities, work is done at every angle, it just so happens that the product of the force and distance (or cos of the angle) just so happen to equate to 0 in some instances and so we say that total work done is zero.

Answer 11

True enough

Answer 12

@Shane_B

need not necessarily

when you slide down a slope, the friction is doing NEGATIVE work ON you.. but you are not doing a POSITIVE work ON the ground.. :D..