# How does table exert force on me?

1. Jun 2, 2013

### Erika E.

I now this is a very fundamental idea, that when I slam my hand on a table, the force that I exert on the table is also exerted back to my hand, if this were not true then the table would move in the direction that I hit it or I would make a dent in it. This idea is hard for me to grasp, because I don't understand how an inanimate object can get energy to exert force on my hand? I think it has something to do with the atoms, and the energy they hold, maybe? Thanks.

2. Jun 2, 2013

### stevendaryl

Staff Emeritus
When you slam your fist down on a table, the table compresses slightly, just like a spring. The force of the table on your hand is the resistance to compression.

3. Jun 2, 2013

### Drakkith

Staff Emeritus
When your hand contacts the table the atoms and molecules in the table repel those in your hand. This force requires no energy to work, as atoms are made of charged particles that always exert forces on things around them and never stop. In fact, energy is a result of these forces acting on objects and accelerating them. For example, a book sitting on a table is repelled by the table, otherwise it would pass through it, yet no energy is expended and no work is performed on either the book or the table.

4. Mar 13, 2016

### AndrewBerkeley

The resisting force provided by the table is NOT the force of atoms and molecules repelling those in your hand and it has nothing to do with the charge of particles. It is the strength of the structure of the atoms and molecules, the rigidity of the material, and it's resistance to compression. Consider what would happen if you slapped the surface of water vs. a pillow vs. a wooden table.

5. Mar 13, 2016

### Drakkith

Staff Emeritus
To clarify, the rigidity of the table is exactly what you said it was and is the reason the table doesn't collapse. The force repelling your hand works just like I said it does.

Absolutely.

6. Mar 13, 2016

### FactChecker

@Erika E., You are right about the energy coming from molecular forces. You have probably not realized the strength of molecular forces in a solid object. They are enormous compared with the forces that we are used to observing in daily life. Most people think that the force of gravity is strong. When something falls 30 feet, it is pulled by the entire Earth and accelerates to a fast speed in that 30 feet. If it hits concrete, it will stop dead in millimeters just from the molecular forces in that tiny impact area. Those local molecular forces are many orders of magnitude stronger than the gravitational attraction of the entire Earth. That is where the energy comes from.

7. Mar 14, 2016

### The Vinh

All you need to know is Newton's Third Law, that's all. You don't have to care about energy, mocule or quantum or even temperature of black hole.

8. Mar 14, 2016

### hackhard

best way to grasp this is to change your perspective of motion .
an ant sitting on your hand as you hit table, will instead think that table (along with planet earth) is hitting your hand, not the other way round