Wall Acceleration: Physics Noob's Curious Query

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Discussion Overview

The discussion centers around the concept of force as described by Newton's third law, particularly in the context of pushing against a wall. Participants explore the nature of forces, acceleration, and how to measure forces in scenarios where neither the wall nor the person pushing it accelerates.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the origin of the force exerted by the wall when pushed, noting that the wall does not have mass or acceleration.
  • Another participant explains that objects only accelerate if there is a net force acting on them, and that other forces (like the ground) prevent both the wall and the person from accelerating.
  • A participant seeks clarification on how to calculate the force exerted by the wall if neither party accelerates, referencing the formula F=ma.
  • One suggestion for measuring the force involves using a spring scale or measuring the deflection of a beam under pressure.
  • There is a discussion about the formula for net force, with some participants emphasizing that it may not apply directly in this context.
  • Another participant introduces the idea that the wall and the person's hands compress slightly when force is applied, which relates to the amount of force exerted.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of force and acceleration, with no consensus reached on the application of the force formula in this scenario. Multiple competing views on how to conceptualize and measure the forces involved remain present.

Contextual Notes

Participants highlight the importance of considering net forces and the effects of other forces acting on the wall and the person. There is an acknowledgment that the relationship between force and acceleration may not be straightforward in this context.

classicalguss
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I'm a bit of a physics noob, but I am always curious about everything in the world.

I concluded from Newton's third law that when you exert a force on a wall it exerts a force back on you. But I want to know from where does that force actually come?

I mean ok you as a person might have a mass and an acceleration, but the wall doesn't though, so how come it has a force that it exerts on you? Does the wall accelerate to begin with?
 
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The wall or you--or any other object--will only accelerate if there's a net force on it. When you push the wall there are other forces acting on the wall (such as the ground) which prevent it from accelerating. Similarly, when you push the wall you don't accelerate either (unless you're standing on a puddle of oil) since the ground also exerts a force on you.
 
Thanks for the reply, and I think things are more clear now. The formula for Force though is F=ma. But since you said neither I or the wall accelerate, then how does it come, or better put, how would you ever calculate that kind of force.
 
To measure it directly, you could do something like put a spring scale between you and the wall. If it's some other structure, for example a beam which you know the properties of, you might measure the deflection of the beam when you push on it. (This is how a beam torque wrench works).

Anyhow, despite not contributing to any motion, these reaction forces have important implications -- for example, you might like to know how strong your wall needs to be.
 
classicalguss said:
The formula for Force though is F=ma.
That's a formula for net force, better written as: ΣF = ma.
But since you said neither I or the wall accelerate, then how does it come, or better put, how would you ever calculate that kind of force.
To produce an acceleration, all you need is a net force.
 
Doc Al said:
That's a formula for net force, better written as: ΣF = ma.
In other words, there are lots of other equations for force and that one doesn't really apply here.
 
If you push on a wall, the surface of the wall compresses a bit, similar to a sping. So does the surface of your hands, if you're pushing with your hands. The amount of compression corresponds to the amount of force (it's probably not linear like a spring though).
 

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