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

• B
• Lotto
Lotto
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?
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?

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?

berkeman
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.

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

phinds

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