Why don't we crumble under our own weights?

Question

I know it seems like a funny and silly question but, I am serious! lol.

When we hold a book, our hands are holding it against the gravitational force of the whole earth (WHOA!) which has only been made possible by the electrostatic force between the charged constituents of our hand and the book at the surface in contact.

I know electromagnetic force is intrinsically so much stronger than gravity and that's what keeps us from collapsing.

But, shouldn't the electrostatic forces cancel out each other as the book and our hand are *almost* electrically neutral?

And even if they don't, why is electrostatic force *in this particular case* always negative (Attractive)?

There HAS to be an answer because gravity hasn't collapsed my chair or me yet. What force counters gravitational attraction? What makes it work in the opposite direction of gravitational attraction?

How did you like the question?

Answer 1

Great question! If you could grab two (negatively charged) electrons and force them together, their resistance (repulsion) would grow nearly without limit as you forced them nearer and nearer per the inverse square law. Because your hand and the book are composed of atoms (and molecules) that are surrounded by electrons (all negatively charged) the book can not be forced into your hand and is supported (repelled) by trillions of electrons at the "surface" of your hand. Your bones can not compress (and crumple) because the calcium atoms and bio-molecules repel each other. Of course if the human body could be separated into a skeleton and gallons of water, the water can crumble (as a liquid) because even though the water molecules repel each other they can flow and fill a container much like a gym filled with basketballs all attracted to the floor by gravity. As a matter of fact, bones lose much of their calcium (and strength) during long hospital stays and only exercise (resisting gravity) makes them strong enough to support our weight.

Answer 2

Gravity is so weak that the attraction between you and the entire Earth can be counteracted by a thin layer of atoms in the area of your footprint. The electron shells around the protons in your foot are just slightly compressed by your weight. The forces between the atoms and molecules in your feet aren't nearly as strong, but it still takes hundreds or even thousands of pounds per square inch of pressure to separate them. Given enough gravity, you would crumble, though. Don't try standing on Jupiter!

Answer 3

I'm strongly reminded of the (only) question in my physics exam, "what forces do you know"... (the answer took me about an hour)

The force holding up the book is not the electrostatic force between hand and book. Holding the book in your hand will have your arm counteracting the gravitic pull on the book. Friction stops the book from slipping between your fingers.

Our body uses the skeleton to avoid settling down into a blob, kept in position by muscles.

The bones in our skeleton are lots of single crystals intergrown with each other. They don't collapse easily under weight pressure because electrostatic attraction and repulsion at very short distances is many orders of magnitude higher than the gravitic force. For the moment, let's assume that the mass you need to crumble a bone at earth surface gravity is several times that of the human body.

The bones are held apart by cartilage material which is made up from proteins. This material is a three-dimensionally linked assemblage of protein fibres with interstitial liquid. The liquid is enclosed, and vertical pressure is transformed in lateral pressure against the membranes. What was a pushing exercise now is transformed into a pulling exercise. For the pulling strength of peptide bonds, consider nylon.

Keeping the bones and cartilage in the joints in place is the responsibility of muscles. Again, this becomes a pulling exercise, actuated by lots of fibres connected to one another via reversible complexes with calcium ions. This is the weakest force so far, but still way stronger than the force needed to pull two flat plates of 1 square foot connected by a fine film of water apart because we have dipols interacting with ions.

Between these fibres is liquid and fatty material enclosed in membranes - our body cells. Lots of weakly inflated balloons pressed or actually linked together. This explains how the flesh and skin of our fingers gets compressed when grasping the book.


Basically, it all comes down to the distances across which the forces work. Inside our body, close distances, towards the mass center of earth, long distance. Short distance wins.

A fun question...

Answer 4

before this discussion answer my question that why doesn't the earth collapse because even your body is applying the same force on the earth.

i agree with Claudie vois.
there are so many other parameters that are required.
i will try to give you a hint in the right direction...
its a fact that because of the atmosphere surrounding us the force on our body because of the earth's atmosphere is almost around weight of 10 elephants.
but still our body doesn't get deformed because the internal pressure of our body balances out the external atmospheric pressure.
this could be one of those parameters but still there will Be so many other things involved.



and most important of all
newton's third law : action and reaction are equal and opposite but they act on different bodies.... here if you consider only book (or hand ) as your system then only electrostatic force of attraction or repulsion should be considered.
but if you consider hand and book as your system than forces acting on the book and the hand being internal forces cancel out each other... so in this case what increases is the mass of the system.

Answer 5

I cant agree with you on these comments as there are thousands of other factors which you have left out in this equation besides gravity versus electrostatic forces + weight of the book. What about the fact that these factors would be only correct if camparing dead weight. The human is a much more complex scenario & it would take several lifetimes before an answer could be concluded.

I am not sure as to weather this was well thaught out on your behalf so I cant say if I liked it. I may be wrong but you would have to prove this to me.

Let me know what conclusions you come to.

Answer 6

Hello,Listen Mr. BATMAN my answer can't be as long as your answer but i will try.:)....so keeping aside your very informative details regarding question i want to say that, we don't crumble under own weight because "weight" is actually gravitational force acting on any object and gravitational force is a central force.According to one of the greatest scientist of this century Mr. NEWTON none of the force can be isolated in nature so it doesn't matter wheather whole earth is attracting us with gravitational force or anything.so don't under estimate yourself you too acting force of the same magnitude on earth.So,its impossible to be crumbled under our own weights.By the way you need not to worry,you will not fall from the place where you are hanging....thank you :P

Answer 7

Gravity is a force which typically a compression force. A LIVE body functions mainly under TENSION force (or STRESS) which is greater thus we have the force to move. When we DIE, the tension force drops to zero and we crumble under our own weights due to the gravitational force!

Answer 8

You know, Dear Abby printed a letter, some time back, that complained of the exact same thing. Talked about how the youth of today are slobs, have no respect for their elders, talk like morons, etc. It was written some two thousand or more years ago by Aristotle! We all feel that way about the next generation!

Answer 9

Different elements have different charges. You are not the book in your hand. You are kinda comparing yourself to a drop in an ocean. I am not the things around me. They are not the earth below me. They are various different elements with different charges and chemistry. Charged atoms never really touch they will always repel themselves and deflect whatever the other element is. If atoms didn't do that then you would be the ground you walk on and everything you touch you would become.

Answer 10

Gravity.