Question

Well , i wanna know WORK by a machine can be Negative or not ?????

Answer 1

no worl is scalar can no be done in negative direction. . .

Answer 2

i had a question by my Academy sir and he asked me this question and asked a example ... i didnt know example so i wrote just yes so he gave me half marks .... but when i asked from my school teacher he said this cant be... i just wanna justify this

Answer 3

work done is force*distance
force and distance both are scalar so work is scalar
you move a stone from at a distance d away from its original place and put it back there then work done is 2d not 0
work done has no direction so can not be negative

Answer 4

thanks ...

Answer 5

Actually it's more complicated than that, @theyatin & @AhsanAJ97


distance = |displacement|
So distance MUST be positive, always. (and "always" is a rare thing in science)

Force can be positive, the magnitude of a force always is because again, absolute value. However, the direction of a force can make it negative depending on how you define it.

Example?

x-component here: \(\large F_x = F \cos \theta\)
y-component here: \(\large F_y = F \sin \theta\)

But what if it's this?

We have a negative for sin\(\theta\). Oh noes negative force! This can't be!!!!



Actually, it can. A negative sign in front of your answer for work (units in Joules, BTU, ft-lbs, etc.) is perfectly valid in the laws thermodynamics, it just means energy is being release from the system to the environment.

In the case of falling object? Energy is release. In the case of fire burning paper? Energy is release.


What's important here is to realize the context and the assumptions you are making. In the falling object, it had potential energy to begin with and the NET change is a release of energy. We ASSUMED that down was "negative" in the vertical direction, so we get our answer as negative. In the combustion reaction, which is highly exothermic in this case, the cellulose fibers in the paper and the O\(_2\) gas in the air were at a higher chemical potential before the reaction, heated gases (and soot) were released as it burned.


This goes back to the question of do you understand the concept of what a vector is?