Newton's third law and energy transfer

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Discussion Overview

The discussion revolves around the implications of Newton's third law on energy transfer, exploring concepts such as work, force, and energy absorption in various scenarios. Participants examine specific examples, including pushing a box, punching a book, and dropping a ball, to clarify how energy is transferred or transformed in these contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how energy transfer can occur if Newton's third law states that every action has an equal and opposite reaction, suggesting that energy would be "given back."
  • Another participant explains that work is defined as force acting over a distance, indicating that energy is transferred when a force moves an object in the direction of that force.
  • A different participant clarifies that Newton's third law pertains to forces, not energy, and notes that energy can be absorbed by an object even if it does not move, such as when a book is punched, leading to deformation and heat.
  • There is a query about whether applying a force requires energy, with one participant asserting that it does not take energy to apply a force.
  • Participants discuss the energy transformations involved when a ball is dropped, noting the conversion of potential energy to kinetic energy and the subsequent loss of energy upon impact.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between force and energy, particularly regarding whether applying a force requires energy. The discussion remains unresolved, with multiple competing perspectives on how energy transfer operates in the context of Newton's third law.

Contextual Notes

Some assumptions about energy transfer and the definitions of work and force are not fully explored, leading to potential gaps in understanding. The discussion also highlights the complexity of energy transformations in different scenarios.

Berney123
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If Newtons third law says there is an equal and opposite reaction how can there be energy transfer.
For example if I push a box and give it 1000 joules of energy wouldn't it "give back" the energy. Also does an object have to be moved for it to gain energy, if I were to punch a book many times would it gain energy or is it just giving back the energy becausE of Newtons third law. And if I drop a ball from a height of 10 feet wouldn't it gain energy after it hits the ground because I am supplying it with potential energy than it is converted into kinetic as it falls once it hits the ground the energy is transferred into the ground and then back into the ball therefore giving the ball more energy than when it started. Please correct me if I am wrong
 
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Recall the definition of work, which is force acting over a distance; the direction of the force matters. If I push a box 1m along the X axis, with a force of 1N, I have expended 1J of energy, because the displacement is in the direction of the force. The box on the other hand absorbed 1J or energy(or rather friction did), as the force it applied was opposite the displacement.
 
Welcome to PF!
Berney123 said:
If Newtons third law says there is an equal and opposite reaction how can there be energy transfer.
For example if I push a box and give it 1000 joules of energy wouldn't it "give back" the energy.
Newton's 3rd law is about force not energy. If you apply a force to a box, it applies a force back at you.
Also does an object have to be moved for it to gain energy, if I were to punch a book many times would it gain energy or is it just giving back the energy becausE of Newtons third law.
There are different kinds of energy. If you punch a book a bunch of times and it doesn't move, it will absorb energy due to deformation and heat up.
And if I drop a ball from a height of 10 feet wouldn't it gain energy after it hits the ground...
It loses potential energy and gains kinetic energy until it hits the ground. Then it loses the (linear) kinetic energy too, converting it to heat and sound.
 
In my first question you said that the box applies a force back to you, but doesn't it take energy to supply a force. And in the second question about punching the book, would the same outcome happen to any object punched repeteadly.
 
Berney123 said:
In my first question you said that the box applies a force back to you, but doesn't it take energy to supply a force.
...
No. It does not take energy to apply a force.
 

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