Work = the resisting force? (Physics)

[saltyload]

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If there is a crane picking up a beam, is there zero work when moving the beam side to side and only has work when it is being lifted perpendicular to the surface of the ground? Does this conservative force only depend on displacement?

If I'm pulling a 10kg crate that has a frictional force of 20N, why is the work done equal to the distance travelled times 20N? Do I not take into account the weight of the crate? Does nonconservative forces involving friction only depend on the force of impeding motion?

 

[lorenzomicron]

work is defined in a specific direction, i.e. the direction in which the force is being applied. thus, if given the force to lift a beam up, only the displacement in the direction of the force matters.

in the 2nd problem, the weight of the object directly correlates to the frictional force, so Ff= mu*Nf, where Ff is the friction, Nf is the normal force (weight in this case), and mu is the frictional coeff.
once again, keep in mind, direction of force and direction of movement; since the friction force resists the motion of the object, then overcoming it requires at least that much force, so then W= Ff*displacement.

Conservative forces do depend on displacement. They are defined as forces which act to produce the same work regardless of the path taken between two points. In a way, it is actually "independent" of the path, but dependent on the displacement.
Non-conservative forces are forces which are not conservative as defined above; in that case, the amount of work would change depending on path, not necessarily due to impeding motion.

 

[saltyload]

work is defined in a specific direction, i.e. the direction in which the force is being applied. thus, if given the force to lift a beam up, only the displacement in the direction of the force matters.

in the 2nd problem, the weight of the object directly correlates to the frictional force, so Ff= mu*Nf, where Ff is the friction, Nf is the normal force (weight in this case), and mu is the frictional coeff.
once again, keep in mind, direction of force and direction of movement; since the friction force resists the motion of the object, then overcoming it requires at least that much force, so then W= Ff*displacement.

Conservative forces do depend on displacement. They are defined as forces which act to produce the same work regardless of the path taken between two points. In a way, it is actually "independent" of the path, but dependent on the displacement.
Non-conservative forces are forces which are not conservative as defined above; in that case, the amount of work would change depending on path, not necessarily due to impeding motion.

I completely forgot about the normal force in frictional force. Thanks.

One more thing, a nonconservative force depends on path, which would be distance and not displacement. Correct?

The second problem shows a top down view of a crate being move up 5m, right 10m, down 5m, and right 10m. The distance is 30m, but the displacement is 20m. So I would multiply the frictional force(20N) by 30m to get the work done.