Does an impulsive force produce any work?

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In summary, the conversation discusses whether an impulsive force produces any work within the abstraction of basic mechanics and an inelastic impact. The concept of an impulsive force is described as a convenient way of summarizing the effect of an ordinary force over time. It is noted that any forces which are perpendicular to the displacement cannot be considered impulsive. The idea of infinitesimal time and infinite forces is also discussed, with the reminder that if energy is lost or gained, work is done. The conversation concludes with the understanding that, in real life, the work of an impulsive force can be calculated through other considerations, such as changes in kinetic energy.
  • #1
valleyman
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Studying it within the abstraction of basic mechanics, with the schematization of impulsive forces (so with no effect of external forces during the impact) does an impulsive force produce any work? I've been discussing about this with a friend, as I think they don't, but we still didn't find a final solution or definition. More in particular, within an inelastic impact, do agent forces produce work?

I thought that considering that the time is considered infinitesimal there can't be any movement or shifting of an object under the effect of those forces, whereas Space = velocity * time. Conseguently, there shouldn't be any work, having that work is Work = Force * Space. This would mean also that friction forces cannot be impulsive forces, as they always generate negative work.

Am I wrong?

Thanks for interesting :smile:,
Valleyman
 
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  • #2
valleyman said:
… does an impulsive force produce any work?

in particular, within an inelastic impact, do agent forces produce work?

I thought that considering that the time is considered infinitesimal there can't be any movement or shifting of an object under the effect of those forces, whereas Space = velocity * time. Conseguently, there shouldn't be any work, having that work is Work = Force * Space. This would mean also that friction forces cannot be impulsive forces, as they always generate negative work.

Am I wrong?

Hi valleyman! :smile:

There isn't really such a thing as an impulsive force (or impulse) …

it's just a convenient way of summarising the effect of an ordinary force over a time …

the actual time is not infinitesimal … but it's convenient to say it is, and to say the force is infinite, and they have a finite product

the only forces which can never be considered impulsive are those which by their nature are perpendicular to the displacement (eg normal forces and magnetic force) …

if energy is lost or gained, then there is work done and so there is an impulse

(and useful tip: if it makes a noise, then work is done! :wink:)
 
  • #3
Hey tini_tim, thanks for replying.

tiny-tim said:
Hi valleyman! :smile:

There isn't really such a thing as an impulsive force (or impulse) …

it's just a convenient way of summarising the effect of an ordinary force over a time …

Well, I imagined something like this, but as I said, I wanted to know the answer within the abstraction (or maybe schematization) of basic mechanics. Raw question could be "if my Physics 1 exam asks to calculate the work of an impulsive force, should I say that it doesn't produce work?

the actual time is not infinitesimal … but it's convenient to say it is, and to say the force is infinite, and they have a finite product
[...]
(and useful tip: if it makes a noise, then work is done! :wink:)

I'm not sure if i understood the sense of the answer well, but it sounds to me that you mean that in real life, while I'm asking what would happen in a hypothetical abstract environment, like those which I studied in the first year of university (that means no noise, no air, no compromises :smile:)
As I see that, in abstract environments infinitesimal time is inappreciable and so is the conseguent movement during this time (as velocity is not infinite).
Is this a wrong way to intend the schematization of basic mechanics?:confused:

Thanks for the help
valleyman
 
  • #4
Hi valleyman! :smile:
valleyman said:
if my Physics 1 exam asks to calculate the work of an impulsive force, should I say that it doesn't produce work?

No … impulsive force usually does work …

the typical example is a bat hitting a ball …

the ball deforms, and the bat remains in contact with it for a very short (but not infinitesimal) time …

the impulse is then calculated as the integral of force times time (and the work done is the integral of force times distance, but some energy is "lost").
in abstract environments infinitesimal time is inappreciable and so is the conseguent movement during this time (as velocity is not infinite).
Is this a wrong way to intend the schematization of basic mechanics? :confused:

Yes … as I said before, it's convenient to say that the actual time is infinitesimal, and the force is infinite, and they have a finite product.

The movement being notionally zero does not matter, since the force is notionally infinite. :smile:
 
  • #5
Following up on what tiny tim said. If you have an infinite force acting over a zero distance then the work is undefined. You will have to determine the work from other considerations like the change in KE.
 
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  • #6
I think I've understood the point, I've lost the bet :biggrin:
thanks for the help
 

FAQ: Does an impulsive force produce any work?

Does an impulsive force always produce work?

No, an impulsive force does not always produce work. Work is defined as the product of force and displacement in the direction of the force. If the force is applied at an angle to the direction of motion, the component of the force in the direction of motion will produce work, while the component perpendicular to the motion will not.

How is work related to an impulsive force?

Work is directly related to an impulsive force. The amount of work done by an impulsive force is equal to the force multiplied by the distance over which the force is applied. This means that a larger impulsive force or a longer distance will result in more work being done.

Can an impulsive force do negative work?

Yes, an impulsive force can do negative work. This occurs when the force is applied in the opposite direction of the displacement. In this case, the work done will be negative, indicating that energy is being taken away from the system.

How is the work done by an impulsive force different from the work done by a constant force?

The work done by an impulsive force differs from the work done by a constant force in two main ways. Firstly, an impulsive force is applied for a very short duration, while a constant force is applied over a longer period of time. Secondly, an impulsive force does not produce a continuous change in motion, while a constant force does.

Can an impulsive force be used to do work on an object?

Yes, an impulsive force can be used to do work on an object. If the impulsive force is applied in the direction of motion, it will result in an increase in the object's kinetic energy. This can be useful in situations where a quick burst of energy is needed, such as in sports or in the operation of certain machinery.

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