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ashtadmir
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If an object moves in such a way that the point of application remains fixed then what can be commented on the work done by the force? (only qualitative analysis required)
No I don't. I was reading conceptual problems of a book when I got this TRUE/FALSE question "work done by a force on an object is zero, if the object moves in such a way that the point of application of the force remains fixed."russ_watters said:Do you have an example in mind? This is typically a misunderstanding of the system definition and how the force is applied.
That doesn't sound right to me either. What book is this question from?ashtadmir said:According to the answers this statement is False.
ashtadmir said:the object moves in such a way that the point of application of the force remains fixed
Doesn't sound right to be either. It is from a famous book in my country for preparation of admission to college. The name is "practice book of physics by DC Pandey". I don't think you would have heard of it.Doc Al said:That doesn't sound right to me either. What book is this question from?
I agree with you, the point of reference must be stated.CWatters said:Badly worded? Fixed relative to what?
If you push a book across a desk against friction the "point of application of the force" can remain fixed relative to the book but move relative to the table.
Isn't the conveyor belt moving? And if the wheel starts rotating, something must have done work on it.ashtadmir said:Now since the point of application of force remains fixed and the center of mass does not move, we can say that the work done by that force is equal to zero.
The conveyor belt is moving but the point of application of force i.e the point of contact between the wheel and belt isn't.Doc Al said:Isn't the conveyor belt moving? And if the wheel starts rotating, something must have done work on it.
That answers my question to satisfaction. Thank you.jbriggs444 said:Work is being extracted from the conveyer because the material at the point of application is moving in the opposite direction of the force applied to that material.
Sure it is! The point of contact between wheel and belt does move (with respect to the room). I think what you're thinking is that, ignoring slipping between the surfaces, the relative motion of wheel and belt is zero. That's certainly true, and it just tells you that the "real" source of the work is whatever is moving the belt.ashtadmir said:The conveyor belt is moving but the point of application of force i.e the point of contact between the wheel and belt isn't.
You are probably thinking of center of mass "work" (or pseudowork).ashtadmir said:I could be wrong about the work, but according to me since there is no net displacement of the wheel therefore work done is zero.
I'm getting there... slowly. (Multi-tasking, and not very well.) :)jbriggs444 said:I am a little surprised not to see Doc Al jump all over this.
I don't get it, how is the point of contact moving with respect to the room?Doc Al said:Sure it is! The point of contact between wheel and belt does move (with respect to the room). I think what you're thinking is that, ignoring slipping between the surfaces, the relative motion of wheel and belt is zero. That's certainly true, and it just tells you that the "real" source of the work is whatever is moving the belt.You are probably thinking of center of mass "work" (or pseudowork).
Isn't the conveyor belt moving?ashtadmir said:I don't get it, how is the point of contact moving with respect to the room?
Doc Al said:Isn't the conveyor belt moving?
Contrast this with an example of a wheel rolling on the ground. In that case, the point of contact of the wheel is (momentarily) stationary. Not so with the conveyor belt.
I'm not quite clear what distinction you are making. When I speak of the "point of contact" of the wheel with the surface, I mean that physical portion of the wheel that is in momentary contact with the surface. What do you mean by "point of contact"?jbriggs444 said:There is a distinction that can be drawn between the material at the point of contact and the point of contact itself.
The point where contact is being made. The position of that point will be a function of time and might even be differentiable.Doc Al said:I'm not quite clear what distinction you are making. When I speak of the "point of contact" of the wheel with the surface, I mean that physical portion of the wheel that is in momentary contact with the surface. What do you mean by "point of contact"?
Ah, now I see what you were saying. I was using "point of contact" as a shorthand way of referring to the physical portion of the wheel that is instantaneously in contact with the surface. And I see where my use of that term could lead to confusion. Thanks!jbriggs444 said:The point where contact is being made. The position of that point will be a function of time and might even be differentiable.
Work done when the point of application of force remains fixed refers to the amount of energy transferred to an object when a force is applied to it and the point at which the force is applied does not move.
The formula for calculating work in this scenario is W = Fd, where W is work, F is the force applied, and d is the distance over which the force is applied.
Examples of work done when the point of application of force remains fixed include pushing a box across a floor, lifting an object straight up, and holding a heavy object in place.
No, work can be both positive and negative in this scenario. Positive work is done when the force and displacement are in the same direction, while negative work is done when the force and displacement are in opposite directions.
The angle between the force and displacement affects the work done by changing the direction of the force. When the force and displacement are in the same direction, all of the force is transferred into work. When the force and displacement are at right angles, only a portion of the force is transferred into work, and the rest is used to change the direction of the object's motion.