Simple Machines

[Timorito]

Scenario 1.
Box being lift up an incline

Scenario 2. Box being lift straight up from rest

The force to lift up scenario 1 is F=mgsintheta because g is fractionalized. This makes sense to me
The force up scenario 2 is mg.

Work for scenario one is delta mgh
work for scenario 2 is delta mgh.

I might be conceptually confused. My professor says both require the same work. but isnt the work on scenario 1 have a fraction of g, making the total work less´

Why is the force for scenario 2 mg , why doesnt it consider height, it seems as its saying that you can lift it up to an infinite high with the same magniture of force mg. please correct me and brush up the ideas i seem to be confusing work and force here. if i lift something straight up do i put in work in the amount of potential energy that it gains at that height?

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[perpetuallylazy]

The incline allows for the FORCE to be reduced because you're pushing it a greater DISTANCE.

W = Fd = mgh

i.e. The block is easier to move but you're moving for a longer time / distance.

This is the concept of all simple machines: work is energy and stays the same for a given process, but you can make it easier by (usually) increasing displacement.

Hope that helps!

 

[Timorito]

Yes that makes sense to me, but lets say i raise up the box to height h, why is the work the change in potential energy, when u raise the box are u giving it the same energy via your muscles or watever if it was just lying at the same high on top of a cliff... thanks

 

[perpetuallylazy]

Yes, the energy is the same if you're lifting the box or sliding the box upward.

Remember that energy is scalar and work is a state function. If I move a box upward by 10 meters using a pulley, my arms, an incline, etc. the energy required to move the box upward can always be expressed by

PE = mgh

Another way of thinking about it: If I place a box on top of a cliff it will have some potential energy proportional to how high it is off the ground. But how did the box obtain that energy? I had to use energy to move the box (converted energy from one form to another).

If it's still not clear let me know and I'll draw a diagram or something! Best of luck.