When two physical surfaces make contact, we say they are 'touching' each other. This contact may make it appear that two different surfaces are actually touching, but in fact, no atoms of any one object can ever touch the atoms of another! The cool dude on the left is leaning on a wall, which his jacket is 'touching'. At least, it seems that way. But when you look very closely at the two surfaces 'in contact', and understand a little about what atoms are like, you discover that no jacket atoms are touching any wall atoms at all! Here's a simplified explanation of why this is so:

An atom could be described as a positively charged nucleus, surrounded by a cloud of negatively charged electrons. The nuclear forces between these two types of objects is so strong that no earthly conditions can cause the electrons to merge with the nucleus, even though they are opposite in charge. There is always space between them. When two atoms are forced into 'contact' (here, the jacket touching the wall), a similar type of force, electromagnetism, keeps negatively charged electrons from actually making contact with each other. Push as hard as you want; you cannot make two electrons come into contact. And the electrons never touch the nucleus. So the only thing actually 'in contact' is the electromagnetic force between the electrons, and there is always space between them! It's as if you are pushing with similar poles of two very strong bar magnets; you can push one around with the other, but can never force them together. Even standing on the floor, you are really supported by a very thin layer of electromagnetic force; no atoms of your foot actually touch atoms of the floor! But wait a minute ... what about when you cut something!?!! Don't the scissor blades have to touch what they're cutting, in order to cut? No, they don't. Atoms can't touch, remember? They just push against each other with an electromagnetic force. That's what happens with the scissors: Even the sharpest knife doesn't 'cut' ... it pushes apart the atoms of the material it's being used on. The atoms of the knife or scissors blade push electromagnetically against the atoms of cardboard (see the diagram above), spreading them apart. Even when the blade is withdrawn, and the material rejoins (as with flesh cut by a scalpel), the sealing is because of the positive and negative attraction between atoms and molecules with net charges (chemistry!) ... but this is not strong enough to force electrons together, just as it wasn't in the original uncut material. OK, what about sticky stuff? When something sticky attaches itself to a surface, aren't the atoms touching? No again! Stickiness is caused by a net electric charge on the molecules involved (positive attracted to negative). Minnie's lipstick actually sticks to Mickey's face because of electromagnetic charges! But this force, once again, is not strong enough to push the electrons on the outer edges of the atoms into contact; the force of repulsion is too strong. In a chemical bond, atoms may actually share electrons ... but nothing touches anything else! It's all done with forces. How about when you eat something and the atoms of sandwich end up in your stomach and bloodstream? Same story! The sandwich atoms are forced apart by the force from your teeth atoms, pulled apart by the chemical (electromagnetic) attraction of your saliva and stomach acid, mixed together (still never touching), and sent to the rest of your body ... pushed along by the electromagnetic forces of the atoms in your blood. You may be wondering how you can feel things, if you don't actually make contact with anything. For example, when you pick something up in your fingers, you can certainly 'feel' the contact! What's happening? The cave man on the right certainly felt the club when it made contact with his head! Let's examine what actually took place when that happened. Atoms of the club pushed against atoms of his head, and probably moved them around a lot (electromagnetically)! Buried in the skin are nerve cells, which have extra electrons they can release when acted on by a force from outside. These electrons flow along the nerves, atom to atom, eventually reaching the brain, where other cells interpret this electrical signal as 'pain'. At no time did any atoms or electrons actually touch each other; the only 'contact' was the electromagnetic force ( positive and negative) between particles! Friction is just the effect of atoms pushing against each other. On a smooth surface, with few bumps, there is little friction. Most of the atoms can slide right by each other without actually pushing against each other. But no surface is totally free of friction. If you examine any surface under a powerful enough microscope, no matter how smooth it appears to the naked eye, there will be bumps. This will cause atoms to come face-to-face. If the forces between one set of atoms (snow, in this case), are weak, those atoms get pushed out of the way. But this uses up energy. It's called 'friction'. If the atoms are joined by strong forces, as in rock, then they can't easily be pushed away. The forces between these atoms and your ski atoms, supposing that you were skiing on rock, might be enough to bring you to a stop! In either case, it's atoms pushing against each other, at a distance, (electromagnetically), that causes friction. Convinced? O.K., next time you kiss someone, just remember that at no time did your lips actually meet! It was just an illusion. Isn't physics wonderful?!?

FOOTNOTE: If you know a little more about particle physics, you might have realized that it is possible to force an electron to make contact with the protons in a nucleus. This is accomplished artificially by colliding them at relativistic speeds in a cyclotron; the force of the collision is able to overcome the nuclear force. One of the things that can happen when the electron hits a proton is that they can combine to create a neutron. This process also occurs in a neutron star, where the intense gravitational pressure collapses all the atoms of the star, so that all the electrons combine with all the nuclear protons, forming a solid soup of neutrons. You might expect that in this case, we could say that there really is contact made between different atoms. However, our current state of understanding leads physicists to believe that electrons and protons themselves are made from combinations of even smaller elementary particles called quarks, which are held apart by their own forces. So even on the sub-nuclear scale, there is no 'touching'. What is inside a quark is the subject of current research in the field ... a subject for a possible future page here on our site! Resources