- #1
eurekameh
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Shouldn't there be negative work done by the string?
Is Negative Work Possible with a String?
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In summary, the conversation discusses the concept of work done by a string and how it relates to the motion of a disk on a string. It is determined that there is no negative work done by the string in this scenario, as there is no relative motion between the string and disk. The string's role in converting work of gravity into rotational kinetic energy is also mentioned, and it is noted that the tension in the string contributes to the sum of linear forces acting on the disk. The conversation also touches on the force of static and kinetic friction in relation to the motion of a rolling ball, as well as the effect of no friction on the motion of the ball.
Shouldn't there be negative work done by the string?
- #2
collinsmark
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As it turns out, no.eurekameh said:
There would be [negative] work done by the string if the disk's axle was sliding on the string, causing the system to heat up. But that's not what's happening here. Whenever and wherever the string and disk are in contact, there is no relative motion between the string and disk. Given that fact, how does W = F·s apply?
- #3
eurekameh
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Thanks. That makes so much more sense. Am I right in saying that the only thing the string is doing is converting some of the work of gravity into rotational kinetic energy, and if there was no string to begin with, the disk would translate vertically at a faster speed than if the string was there to convert some of the work to rotational kinetic energy?
- #4
collinsmark
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I suppose that's a valid way to look at it.eurekameh said:
The relationship of v = (0.1 m)ω in this case is due to the string, in part. And the tension on the string also contributes to the sum of linear forces acting on the disk (which explain's why the disk's linear acceleration is less than g). The string just doesn't do any work though.A ball of radius r rolling on a hard, flat surface (ignoring air resistance) will continue rolling indefinitely. No work is being on the ball or by the ball. Yet it is the force of static friction that keeps the ball rolling, as opposed to sliding, and thus plays a role in determining the v = ωr relationship.
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- #5
eurekameh
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But if it was sliding instead, the force of kinetic friction would be doing negative work?
Also, if there was absolutely no friction at all, the ball would still be going indefinitely, but without rotation, right?
Also, if there was absolutely no friction at all, the ball would still be going indefinitely, but without rotation, right?
- #6
collinsmark
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Right.
FAQ: Is Negative Work Possible with a String?
1. What is the difference between work and energy?
Work is the transfer of energy from one object to another, or the application of a force over a distance. It is a measure of the amount of energy required to move an object. Energy, on the other hand, is the ability to do work. It comes in different forms such as kinetic, potential, thermal, and chemical energy.
2. Why is there confusion between work and energy?
The confusion between work and energy arises because they are closely related concepts. Both are measured in the same units (Joules) and have similar formulas. Additionally, the term "work" is used in everyday language to mean something different than its scientific definition, which can lead to confusion.
3. How can I differentiate between work and energy?
One way to differentiate between work and energy is to remember that work is a process, while energy is a property. Work is done on an object to transfer energy to it, and energy is what enables the object to do work.
4. Can work and energy be converted into each other?
Yes, work and energy can be converted into each other. This is known as the Law of Conservation of Energy, which states that energy cannot be created or destroyed, only transferred or converted from one form to another.
5. How can I avoid confusion between work and energy?
To avoid confusion between work and energy, it is important to understand their definitions and how they are related. It may also be helpful to use specific examples to solidify the concept. Additionally, using proper scientific terminology and avoiding colloquial language can help clarify the distinction between the two.