What forces act on a bar when you do pull-ups?

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Discussion Overview

The discussion revolves around the forces acting on a bar during pull-ups, exploring the relationship between body weight, acceleration, and the force exerted on the bar. Participants consider both static and dynamic scenarios, including the implications of acceleration and the comparison to other exercises like push-ups.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that when hanging still, the force on the bar equals the individual's weight, while during a pull-up, the force may increase due to the need to overcome inertia.
  • There is a question about whether the speed of the pull-up affects the force exerted on the bar, with one participant proposing that a slower pull-up might differ from a faster one.
  • One participant states that if there is no acceleration, the force on the bar equals the weight, but if there is acceleration, the force exerted is greater than the weight, with the force increasing with greater acceleration.
  • Another participant elaborates that the force on the bar varies throughout the pull-up, suggesting it decreases as the arms contract and increases again during downward acceleration, proposing a periodic function of force over time.
  • Some participants express frustration regarding the clarity of the discussion, indicating a desire for more guided responses rather than direct answers.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact nature of the forces involved during pull-ups. There are multiple competing views regarding the effects of acceleration and the relationship between body weight and the force on the bar.

Contextual Notes

The discussion includes assumptions about equilibrium and acceleration, but these are not universally agreed upon. The mathematical relationships and functions proposed are not fully resolved, leaving room for interpretation.

Lotto
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TL;DR
If you do pull-ups, a force acts on a bar when you move upwards. Is the force twice your weight or has it the same value?
I am not sure here, even though it is probably simple. If you just hang on the bar and don't move up, you act on the bar with a force equal to your weight. But when you want to do a pull-up, I would intuitively say that you act on the bar with a higher force.

But when I think about it I would say that when you move upward, you have to apply a force equal to your weight in order to make your body move (let's say we don't want to accelerate). So does that mean your body "levitates" and its weight doesn't count to the total force acting on the bar? The only force acting on it is only the force I am using to move my body?

Does it work the same way when doing push-ups? If I did it on a bathroom scale, would it show still the same value?
 
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Do you reckon it matters how fast you pull yourself up? Is a really slow pull-up the same as a very fast pull-up?
 
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Lotto said:
TL;DR Summary: If you do pull-ups, a force acts on a bar when you move upwards. Is the force twice your weight or has it the same value?

(let's say we don't want to accelerate)
If you don't accelerate then you are in equilibrium and the force on the bar equals your weight. But if you do accelerate then the force ##F## that you exert is greater than your weight ##w##. The greater your acceleration the greater the value of ##F##.
 
Mister T said:
If you don't accelerate then you are in equilibrium and the force on the bar equals your weight. But if you do accelerate then the force ##F## that you exert is greater than your weight ##w##. The greater your acceleration the greater the value of ##F##.
And the force on the bar will be less than your weight as your arms get closer to full contraction until you stop and then as you accelerate down until you reach constant velocity again but down. So force as a function of time will be a periodic function, roughly sinusoidal, with a baseline at your weight.
 
Mister T said:
If you don't accelerate then you are in equilibrium and the force on the bar equals your weight. But if you do accelerate then the force ##F## that you exert is greater than your weight ##w##. The greater your acceleration the greater the value of ##F##.

kuruman said:
And the force on the bar will be less than your weight as your arms get closer to full contraction until you stop and then as you accelerate down until you reach constant velocity again but down. So force as a function of time will be a periodic function, roughly sinusoidal, with a baseline at your weight.

Guys, I was trying to LEAD him to that, not spoon feed him the answer.
 
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phinds said:
Guys, I was trying to LEAD him to that, not spoon feed him the answer.
Oops, sorry.
 
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