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

In summary, during pull-ups, several forces act on the body and the bar. These include gravitational force, which pulls the body downward, and the tension force generated in the arms and shoulders as the individual pulls themselves upward. The bar experiences an upward tension force from the body while also undergoing a downward force due to gravity acting on the body’s weight. Additionally, friction between the hands and the bar can play a role in grip stability. Overall, these forces interact to facilitate the movement of the pull-up.
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Lotto
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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?
 
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  • #2
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##.
 
  • #4
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.
 
  • #5
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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FAQ: What forces act on a bar when you do pull-ups?

1. What forces act on the bar during pull-ups?

When performing pull-ups, the primary forces acting on the bar include the gravitational force acting downwards due to the weight of the person, and the upward force exerted by the person pulling themselves up. Additionally, there are reaction forces from the bar itself, which are equal and opposite to the forces applied by the person.

2. How does the weight of the person affect the forces on the bar?

The weight of the person directly influences the gravitational force acting on the bar. As the person pulls themselves up, this weight creates a downward force that the bar must counteract. The greater the weight of the person, the greater the force that the bar must withstand during the pull-up motion.

3. Are there any other forces at play besides gravity and the pulling force?

Yes, in addition to the gravitational force and the pulling force, there are also dynamic forces involved. These include the inertia of the body as it moves upward and any lateral forces that may occur if the body sways or shifts during the exercise. Friction between the hands and the bar can also play a role, although it is generally minimal compared to the other forces.

4. How does the angle of the body affect the forces on the bar?

The angle of the body during a pull-up can change the distribution of forces on the bar. If the body is more vertical, the force exerted on the bar is primarily vertical. However, if the body is angled or swaying, some of the force may act at an angle, which can introduce additional horizontal forces that the bar must support.

5. What happens to the forces when a person uses different grip positions?

Different grip positions can affect the distribution of forces on the bar. For example, a wider grip may require more lateral stability, increasing the horizontal forces acting on the bar. Conversely, a closer grip may allow for a more vertical pull, concentrating the forces in a downward direction. Each grip position can also engage different muscle groups, potentially altering the overall force dynamics during the pull-up.

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