# Macroscopic interaction of objects

Discussion in 'Physics' started by logicman112, Feb 14, 2011.

1. ### logicman112 Thread Starter Active Member

Dec 27, 2008
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When two objects hit each other they repulse each other exerting fore. What is the type of this force? Electrical, Magnetical, gravitational, atomical?
It seems that force is none of the above!!

2. ### DumboFixer Active Member

Feb 10, 2009
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How about the transfer of kinetic energy ?

3. ### Wendy Moderator

Mar 24, 2008
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Would you believe electromagnetic? It is the force that binds matter, and keeps matter from interpenetrating. That one I remember from a physics TV show a long time ago.

4. ### logicman112 Thread Starter Active Member

Dec 27, 2008
69
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but electric forces are between two charged bodies. In our case we have two objects without charge! and magnetic forces exist when charge is on the move, we do not have charges here. Suppose we throw an electron towards a neutron, when they hit each other, the moment of each one changes. What is the type of force they exert on each other?

5. ### fila Member

Feb 14, 2011
64
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If two objects hit each other and none of them breaks apart that means that there wasn't enough energy to brake the bonds between molecules. You have covalent, metal and ion bonds but essentially those are all types of electromagnetic forces. Some are strong and some are weak. So if you imagine your objects as molecules you can say that because of the insufficient kinetic energy (force, pressure) those molecules were able to repel each other.

Aug 27, 2009
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7. ### Papabravo Expert

Feb 24, 2006
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Collisions come in two flavors: elastic and inelastic. In the first case imagine two tennis balls colliding. The rubber material is like a spring which converts kinetic energy to potential energy proportional to the displacement. When this process is complete and the velocity of both balls goes to zero. The potential energy stored in the spring accelerates the balls in the opposite direction.

The inelastic collision, of cue balls for example, is just a stiffer spring with a smaller deformation.

What kind of force is it you ask. It is a force that comes from acceleration: Newton's 2nd Law. When the acceleration is due to gravity it gives a mass a property called weight. Other types of acceleration give rise to a similar type of forces except the magnitude does not depend on the two masses or the distance between them, as is the case with gravity.

We are talking macro scale here, not quantum mechanics or special relativity.

8. ### logicman112 Thread Starter Active Member

Dec 27, 2008
69
2
We only have 3 types of forces in this world:
Gravitational, electromagnetic and atomic regardless of the type of physic we want to use(Classic, quantum...). My question is that in that scenario, what is the type of our force?

9. ### Papabravo Expert

Feb 24, 2006
10,144
1,791
You are misinformed. The four forces you are referring to are part of the Standard Model for particles smaller than an atom. There is nothing in Newton's 2nd law that says anything about gravity, electromagnetism, the strong force, or the weak force. There is just mass and acceleration to be concerned with. To be more precise there is just the time rate of change of momentum that gives rise to a force -- period, full stop. It is of course true that gravitation extends to the macro scale and has no distance limit.

Last edited: Feb 15, 2011
10. ### Wendy Moderator

Mar 24, 2008
20,766
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Going with what Papabravo said, there are 4 forces. The holy grail of physics is to link gravitational with the others, which are strong force, weak force, and electromagnetic. The latter three are connected in physics, but merging them with gravitational still eludes.

Funny thing is, when I started this post I thought there were 5, somewhere during my lifetime 2 have been merged into one force.

There is no such thing as atomical. A little reading goes a long way.

http://en.wikipedia.org/wiki/Fundamental_interaction

If you go to the end of that article you will find links to lots more reading material. That same article mentions how electromagnetic makes matter solid, though it is deep reading.

11. ### Papabravo Expert

Feb 24, 2006
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An interesting article. The crux of the OP's question however was "which of the four is involved in the collision of two objects"? My answer was none of them because the forces involved are not "fundamental". The force is rather a derived force arising from a time rate of change of momentum. As Newton observed, the time rate of change of momentum has nothing to do with any of the fundamental forces.

12. ### Black-Bird New Member

Jan 26, 2011
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Mechanical Force ?

13. ### logicman112 Thread Starter Active Member

Dec 27, 2008
69
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Papabravo, suppose a neutron hits an electron. They exert force on each other probably and are deflected. What is the fundamental force behind this?

14. ### BillO Well-Known Member

Nov 24, 2008
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Please don't take this the wrong way, but this is not true.

Elasticity has nothing to do with the amount of deformation, but rather the amount of energy consumed by the deformation. In a highly elastic collision most of the kinetic energy will be conserved. In a highly inelastic collision, most of the kinetic energy will be converted to a less accessible form (most likely thermal).

Good pool balls have elastic collisions, good crash helmets have inelastic collisions.

Edit: And, sorry, but this is a simplification (to limted example) of the situation. Elasticity is a big subject.

Last edited: Feb 28, 2011
15. ### bribri Member

Feb 20, 2011
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whatever you call it, it's the same one that got them moving in the first place.

Last edited: Mar 1, 2011
16. ### russ_hensel Well-Known Member

Jan 11, 2009
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the bodies are net neutral but not so microscopically. the repulsion is electrical.
in some way solid objects are so full of space that without these forces ( electric ) 2 objects could occupy the same space at the same time. the electric force also holds molecules together and solids and liquids together.