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Say for instance a person who was strong enough to lift double his body weight. If he placed his hands under his bottom and tried to lift$^1$ himself$^2$ off the ground, could he?


$^1$In a slowly, controlled motion; sudden jumps etc. are excluded.

$^2$ All parts of himself without touching or being supported by the ground in any way.

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2ünchhausen Baron Von Munchhausen lifted himself out of the quicksand – Bernhard Aug 1 '12 at 17:38
My father used to tell me about our mythical ancestor Bootstrap Thompson, the only man in the world who could pick himself up by his bootstraps and hold himself out at arm's length. – Keith Thompson Aug 2 '12 at 0:17
The question is ambiguous. If you push down against the ground, it's possible. If you try to pull up against your own body, it's not. – Keith Thompson Aug 2 '12 at 0:18
Taken as what the open should have said then no because you can not pick yourself up in this manner unless you have a higher mass objects to offset the force. The wording is very non-specific. – Argus Aug 2 '12 at 14:00
I don't know why this is downvoted... he asked a thought question which plays with the ideas of Newton's Laws, and there is an answer to this question. I see so many retarded questions on this forum of people pretending to understand "advanced physics" and they get 200 upvotes, when the answer is completely trivial (or the question just doesn't make sense)... – Chris Gerig Aug 3 '12 at 5:45
up vote 2 down vote accepted

No, it's not possible.

Why? Think about, for a second, what you're trying to achieve. The most important concept that you're missing is that a force is an interaction between two objects. One applies a force to the other and the other applies that same force back. You might be wondering how anything gets done/moved then?

Well, if you think about the simplest mathematical expression of force $F= ma$, it shows that the force exerted is the product of mass and acceleration. When we say that an object exerts the same force on an object, it does. But the gist of it is that objects differ in mass. Sometimes drastically.

$$m_1a_1 = m_2a_2$$ $$F_{1\rightarrow2} = F_{2\rightarrow1}$$

Here's that in written form. Object 1 applies a force to Object 2. An interaction. Object 2 applies a force to Object 1. Forces are equal, yet, they move. Why? Think about it, if object 1 has $m_1 = 100m_2$ (100 times the mass of object 2) and exerts a force of, let's say, 300 N on it, it will move it without breaking a sweat. Object 2 will apply that same force on it, but because it has such low mass, it won't make even a dent in the acceleration of Object 1. That's a crucial part of that interaction. Here, even the math agrees:

$$100m_2a_1 = m_2a_2$$ $$100a_1 = a_2 $$

The acceleration of object 2 is, linearly, 100 times bigger more than object 1. Now, let's get to your problem. Can someone lift himself? You push yourself and yourself pushes you. Since we're talking about the same object, this reduces down to two same masses exerting the same force on each other. And the net force is $0$.

Same goes for cartoonish ideas like moving a boat by blowing into the sails. This is a repercussion of the translational symmetry of our Universe, conservation laws and common sense™. Hopefully, this is simple enough to make you see why it doesn't "work".

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A better way to say this: Newton's Law is for external forces, but pushing on yourself is an internal force, giving zero acceleration. – Chris Gerig Aug 3 '12 at 4:18
@ChrisGerig True enough, but this is just a bit more expressive since the OP didn't seem convinced. – Domagoj Pandža Aug 3 '12 at 4:21
@ChrisGerig not to forget conservation of momentum too. If the act of lifting exhausted gas :) for example. – anna v Dec 13 '12 at 15:06

NO because you are applying the force to yourself the appliation point and the origin of the force are ate the same point you can not lift yourself as in cartoons :D

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Just step on your hands, you are now lifting yourself.

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Hello Anon. Welcome to Physics.SE. While answering questions, please keep in mind that your answer addresses the question. For me (as a plain user), This is just nothing..! – Waffle's Crazy Peanut Dec 13 '12 at 14:48

The simple answer: yes

@bernhard In the spirit of the question if your arms are long enough and you build enough momentum with your arms then your arms will lift your body off of the ground.

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-1, the question was: can you lift yourself, by putting your own hands under your own bottom. – Bernhard Aug 2 '12 at 5:41
@Bernhard: Yes, and if you put your hands under your bottom and push down, you can lift yourself. The question, IMHO, is poorly phrased. – Keith Thompson Aug 2 '12 at 6:25
Using your wrist as a fulcrum and pushing your hands down ie straightening your wrist. In the wording of the question this is completely possible. – Argus Aug 2 '12 at 13:56
@Argus: Well, not for me. 8-)} – Keith Thompson Aug 3 '12 at 0:37
@Bernhard: I edited my answer to reflect the intended question. – Argus Aug 3 '12 at 1:59

protected by Qmechanic Dec 13 '12 at 15:18

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