In the last installment of Science Friday we discussed how all matter is made of more than 99% empty space. We ended the blog post by posing this question: If all matter is made up of mostly of empty space, why can’t my hand pass through the weld I just made?
Every time I think about this topic, I think of the opening to the Cohen Brothers movie, The Men Who Stare at Goats. If you haven’t seen the movie, here is the opening scene:
As funny as it is to watch a grown man run full speed into a wall and end up on his backside, this clip does illustrate a great scientific concept. If that wall is mostly empty space, why can’t he run through it? Why does it feel solid? Why did it leave him with a wicked headache, a black eye, and no dignity?
The answer is the electrostatic force. The electrostatic force holds electrons and protons together in atoms and allows the atoms of different elements to bond together to form new substances. It is also responsible for the solidity of solid objects. The electrostatic force is summed up in the law of charges: opposite charges attract and like charges repel, just like the opposite ends of a magnet.
Here’s how it works:
The inconceivably tiny atoms that combine to make all of the living and non-living things around us are made of the same three particles: protons, neutrons and electrons. Protons have a positive charge and electrons have a negative charge. Neutrons, as their name suggests, have no charge. The protons and neutrons are tightly packed in a central nucleus. Electrons, which are almost 2,000 times smaller than protons and neutrons, are found whizzing about outside the nucleus in regions that scientists call shells or orbitals. If the nucleus were the size of a golf ball then the nearest electron would be about a mile away. The space in between is mostly empty space!
The negatively charged electrons are held in orbit around the nucleus because they are attracted to the positively charged protons. Electrons play an electric balancing act; trying to get as close as they can to the nucleus while keeping as far away from each other as possible. The liked-charged protons in the nucleus don’t repel each other because protons themselves are made of even smaller particles called quarks. These quarks create a strong nuclear force that holds the nucleus together.
The behavior of magnets gives us a sense of the attractive and repulsive electrostatic forces at play inside atoms. If you hold the north pole of one magnet near the south pole of another magnet, an invisible but very real magnetic force will pull each of them together. If you flip the magnet around and try to push the south poles of each magnet together, the same magnetic force will cause them to repel each other. Unlike poles attract and like poles repel the way that opposite charges attract and like charges repel.
This is a fun little experiment, but what does it have to do with walking through a wall? After all, how many of us wouldn’t love to be able to walk through any wall or door? Well, atoms may be made of mostly empty space, but their outside edges—the part of the atom that you come in contact with when you touch a wall, a door, or any other solid object—is a collection of electrons. Of course, people are also made of atoms, so when the guy in the movie tries to run through the wall, the electrons on the outside edges of his atoms are repelled by the electrons on the outside edges of the atoms that make up the wall. It doesn’t really matter that atoms are mostly empty space between the nucleus and the electrons because when it comes to everyday objects we’re really only dealing with electrons!
If you head has not exploded yet, it will…
This is why you never really touch anything. Take two fingers and push them together. It feels as though they are touching, right? Each finger feels solid. You can feel the fingers pushing against each other. However, if you were to look at your fingers at the atomic level you would see that they never come into contact with one another! Your fingers are actually feeling the electrons in the atoms of one finger pushing against the electrons in the atoms of the other finger. This is similar to the repulsive behavior of a magnet when you try to bring like poles together. You feel the resistance of the magnetic force but the magnets never actually touch. This is the illusion of solidity!
When you pick up a welding torch, it feels solid, it has mass and weight. However, you are not in physical contact with the torch. Instead, the electrons in the atoms of the torch are repelled—at an infinitesimally close distance—by the electrons in the atoms of your hand.
Thus the electromagnetic force explains why you don’t fall through the floor even though the floor is made up of more than 99% empty space. This is also the reason why we can’t run through walls… which kind of sucks because I’d like to be able to scare my wife in the kitchen by just popping in through the wall.
If you feel like you missed something here is a quick little video I found that sums this all up:
IN THE NEWS
Happy Birthday Cell Phones!
This week the cell phone turned 40 years old. The DynaTac 8000X, the first commercially available cell phone cost a very reasonable $4,000. Considering that we can put the equivalent of a supercomputer in our pockets for a mere $200 these days, I would say the technology has come quite a long way.