- #1
Vivee=)
- 15
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So I'm trying to push an big object and it doesn't move, am I doing work on it? Or is work 0 joules?
In summary, work is the force applied multiplied by the distance the object moves. If an object does not move, then work done on it would be zero. In the case of a box sliding down a frictionless slope, the equation for work would be W=w*d*cos(90-theta), since the box is moving and work cannot be zero. However, in the absence of gravity and friction, the box would not move at all. This demonstrates that gravity is the active force pushing the box down. The equation for weight, which is weight = mass x gravity, assumes that gravity is a constant of approximately 9.81 m/s^2 on Earth. The removal of gravity was used as an example to show that it is the
- #2
cristo
Staff Emeritus
Science Advisor
- 8,146
- 75
What is the definition of work?
- #3
Vivee=)
- 15
- 0
Work is the force I would apply times the distance the object moves... OHHH, it's that simple. It doesn't move so work would be zero. Thanks cristo.
- #4
Vivee=)
- 15
- 0
Ok, I have another work question. What if the box is sliding down a frictionless slope. Would the equation for work be W=w*d*cos(theta), with w=weight and d=distance? Or would it be W=w*d*cos(90-theta)? I'm guessing it's one of these because since the box is moving, work cannot be zero.
- #5
Math Jeans
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Vivee=) said:
In that case the work would be done by gravity. Calculate the force that gravity is exerting on the box at that angle and relate it to the distance.
You can think of it this way. If there was no gravity, the box would just sit at the top of the slope because nothing is pushing it down.
- #6
Vivee=)
- 15
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Ohh yes, I got it. It must be W=w*d*cos(90-theta) because W=w*d*cos(theta) would find something else.
- #7
Colin1
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Math Jeans said:
What if there was no friction?
- #8
Math Jeans
- 349
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Colin1 said:
Even if there is no friction, nothing is pushing the box down. Space is a vacuum, there is no air resistance. If you are in space, there is no gravity, and no friction, and you still float. So does the box.
- #9
Colin1
- 23
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Interesting
so, if
weight = mass x gravity
is gravity a constant here? If so, what varies as what now that it's been removed?
so, if
weight = mass x gravity
is gravity a constant here? If so, what varies as what now that it's been removed?
- #10
Math Jeans
- 349
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Colin1 said:
Gravity on Earth is approximately equal to 9.81 m/s^2. This changes very slightly at higher altitudes, but the change is so small that it can be left out.
The removal of gravity was just an example in order to show that it was the active force pushing the box down.
- #11
Colin1
- 23
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Math Jeans said:
Sure
I understood that, I was just wondering where the equation went from there
- #12
Vivee=)
- 15
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Oh, I figured it out myself. Thanks for the reply.
- #13
Colin1
- 23
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Yeah
I think I did too
you end up with mass varying as mass or something equally useful
I think I did too
you end up with mass varying as mass or something equally useful
- #14
Loren Booda
- 3,125
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Consider that the object would essentially have to be of infinite mass and perfectly rigid not to perform work on it.
- #15
TVP45
- 1,044
- 5
You should specify that, if the object does not move, you are doing no MECHANICAL work on it. You are, however, doing some combination of elastic work, thermal work, and biological work; it's just that we don't usually count those in this kind of problem.
- #16
AbedeuS
- 133
- 0
Wouldnt it be easier to use Sin(Theta) rather then Cos(90-Theta)?
Edit: Since Cos is just a derivative function of Sin, and is 90 out of phase with Sin anyway, so adding 90 is effectively just superimposing a Cos wave onto a Sin?
Edit: Since Cos is just a derivative function of Sin, and is 90 out of phase with Sin anyway, so adding 90 is effectively just superimposing a Cos wave onto a Sin?
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- #17
AbedeuS
- 133
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In fact scratch that, that would be +90+Theta rather then minus i guess...
FAQ: Is Work on a Static Object Possible?
What is work on a static object?
Work on a static object is the amount of force applied to an object that does not result in any displacement or movement of the object.
What is the formula for calculating work on a static object?
The formula for calculating work on a static object is W = F * d * cosθ, where W is work, F is the applied force, d is the distance over which the force is applied, and θ is the angle between the force and the direction of motion.
Can work be done on a static object?
Yes, work can be done on a static object. However, since there is no displacement, the work done will be zero.
How is work on a static object different from work on a moving object?
Work on a static object does not result in any displacement, while work on a moving object does. This means that work on a static object will always be zero, while work on a moving object can be either positive or negative depending on the direction of the displacement.
What are some real-life examples of work on a static object?
Some examples of work on a static object include pushing against a wall, holding a heavy object without moving it, and carrying a book while standing still.