Questions About Work, Force, and Pendulum

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Discussion Overview

The discussion revolves around the concepts of work, force, and motion, particularly in the context of pendulums and the application of forces. Participants explore theoretical implications and practical examples related to Newton's laws of motion and the nature of work done on objects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether applying a force for an instant while causing an object to move constitutes work, suggesting that work can be approximated as the kinetic energy of the object post-application.
  • Another participant argues that a constant force can lead to constant speed if it is balanced by opposing forces, clarifying that Newton's second law applies to the net force acting on an object.
  • Some participants assert that work only occurs while a force is actively applied, and once the force ceases, no work is being done.
  • There is a contention regarding the claim that applying the exact force to a pendulum to reach its maximum height would result in an infinite time to reach that height, with some arguing that it would reach that point in an infinitely short time instead.

Areas of Agreement / Disagreement

Participants express differing views on the nature of work and the implications of applying forces, with no consensus reached on several key points, particularly regarding the pendulum scenario and the conditions under which work is done.

Contextual Notes

Some claims depend on interpretations of Newton's laws and the definitions of work and force, which may not be universally agreed upon. The discussion includes assumptions about the nature of forces and motion that remain unresolved.

mprm86
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1. If you apply a force to an object only for just and instant, for examples, if you hit a ball with a force of 10 N and it moves 100 meters, are you making work?

2. How can a constant force that is applied to an object during a period of time can make it move with constant speed? According to Newtons second law, F=ma, so the object should accelerate.

3. My teacher says that if we push a pendulum with the exact force it requires to reach its maximum high, the time it will take to reach that point will be infinite. How can this be possible?

Thanks in advance.
 
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2. If the force you apply is balanced by another force, the object can move at constant speed. Think about pushing a block with constant force; if the force you apply is opposed by friction in the opposite direction then a constant speed can be achieved. Newton's second law refers to the net (overall) force acting on the object.
 
Work only happens while the force is being applied. After the force is done, no work is being done.

2. It can't. If a single force is being applied to an object, that object will accelerate according to his second law. Only in the presence of more than one force will variation of this law occur, in which case the principles of superposition will give you the net force.

3. This is not true. If its the exact force required to reach that point, it will reach that point for an infinitely short amount of time and leave. If you were JUST shy of the exact force, it would not reach the point at all. What he said is like saying if you tried to jump up to the moon it will take you an infinite amount of time to get there.
 
1. If you apply a force to an object only for just and instant, for examples, if you hit a ball with a force of 10 N and it moves 100 meters, are you making work?

i was. no one can hit a ball instantly - it always takes some certain time, during which i apply a force and the ball accellerates. The work one makes can be approximated as the kinetic energy of a ball just after the hit.
 

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