Why were momemtum, kinetic energy and work introduced?

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Discussion Overview

The discussion revolves around the introduction and definition of physical quantities such as momentum, kinetic energy, work, and force in physics. Participants explore the necessity and utility of these concepts in explaining natural phenomena, as well as the historical context of their development.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether it is possible to explain nature without defining quantities like momentum and energy, suggesting that it would be much more difficult, if not impossible.
  • One participant argues that these quantities relate different physical aspects in a way that allows for accurate predictions of phenomena.
  • Another viewpoint suggests that the definitions of these quantities are based on their utility in making quantitative predictions, particularly those that are conserved over time.
  • It is noted that these quantities are useful for describing how the world behaves and are tied to fundamental symmetries in Newtonian and special-relativistic spacetime.
  • A historical perspective is provided, indicating that concepts like velocity, acceleration, and forces were developed to better understand motion, leading to the introduction of momentum and energy for more complex scenarios.
  • Participants discuss the naming conventions for physical quantities, questioning why certain derivatives, like the second derivative of momentum, do not have specific names, suggesting it may be due to their less frequent occurrence in equations.

Areas of Agreement / Disagreement

Participants express a range of views on the necessity and definitions of these physical quantities, indicating that there is no consensus on whether alternate quantities could suffice or on the specific reasons for naming conventions.

Contextual Notes

Some discussions touch on the historical evolution of these concepts and their practical applications, but there are unresolved questions regarding the adequacy of existing definitions and the potential for future developments in physics.

hackhard
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why were quantities like momentum, force , potential energy, kinetic energy,work ,etc needed to be introduced in physics?
and why were they defined the way they are defined?.
would it not be possible to explain nature without defining these quantities or by using alternate physical quantities ?
 
Last edited:
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hackhard said:
would it not be possible to explain nature without defining these quantities or by using alternate physical quantities ?

Even if it is possible, it would be MUCH more difficult. I doubt it would even be possible, really.
 
why were quantities like momentum, force , potential energy, kinetic energy,work ,etc needed to be introduced in physics?
 
I'd say that they relate different quantities to one another in a way that makes it possible to accurately predict a wide range of phenomena. I really don't know how to explain it very well. Without all of those concepts, physics as we know it would be much more difficult, if not impossible. Maybe someone else can explain it better. @Orodruin, any idea?
 
hackhard said:
why were they defined the way they are defined?
The quantities were defined based on what is useful to make quantitative predictions. For example, a quantity that is conserved over time is useful to predict what will happen.
 
It was "needed" as it was useful for describing how the world behaves, just as everything else in empirical sciences.
 
These quantities were introduced into physics because they are very useful to describe nature. From a modern point of view you can ask, whether you need forces, but all other quantities (i.e., momentum, energy, angular momentum) are related to the most fundamental properties of our description of nature, i.e., the symmetries of Newtonian and special-relativistic spacetime. These symmetries explain a lot why the physical laws the physicists discovered over the centuries look as they do. The most fundamental discovery is the discovery of these fundamental symmetries.
 
I'll try to answer this question in the chronology of which we study these topics. Before the time of Galileo and Newton most of the ideas about the motion of bodies were quite crude. It was Newton who first gave proper mathematical laws for the motion of bodies. His laws make use of concepts such as velocity (if we're studying motion then what better way to express it than change in position with time?), acceleration and forces ( which basically is the cause of motion or how motion is transferred b/w bodies). This was all well when we are doing problems of kinematics and simple dynamics, but then for problems such as collisions and variable mass systems, the idea of momentum and impulse was needed. Also, there were a different class of situations where the forces varied with distance instead of time, here the ideas of work and energy come into the picture. Some of these quantities, such as momentum and energy, turned out to be quite fundamental and also followed conversation laws.
These concepts are tools used to study the world around us. Why specifically these quantities? Because they seem to work best for us. Many concepts have been dropped in the past because they weren't satisfactory and in the future we probably will get some new quantities which lead to better understanding of nature.
 
a new quantity was defined for rate of change of velocity, momentum,work,etc but no special name for rate of change of acceleration .
was it because rate of change of velocity, momentum,work, occurred frequently in equations ,hence for simplification?
 
  • #11
Drakkith said:
It's called a jerk.
alright aim of my ques was different. if consider second derivative of momentum?
a new quantity was defined for rate of change of velocity, momentum,work,etc but no special name for second derivative of linear momentum .
was it because rate of change of velocity, momentum,work, occurred frequently in equations ,hence for simplification?
 
  • #12
hackhard said:
a new quantity was defined for rate of change of velocity, momentum,work,etc but no special name for second derivative of linear momentum .
was it because rate of change of velocity, momentum,work, occurred frequently in equations ,hence for simplification?

Pretty much. Those quantities which are used the most are the ones which have names assigned to them.
 

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