#12 Gravity

The force of gravity seems like a big deal when you have to get out of bed in the morning, or you're helping a friend move furniture around, or when somebody drops a bucket of rocks and gravy out of a window onto your head. However, compared to the other forces, gravity is pretty weak.

There are four known forces in the Universe. Two of them, the strong and weak nuclear forces, keep atoms from flying apart and stuff like that. You shouldn't be concerned about them unless you are a nuclear physicist. If anybody asks, you didn't hear about them from me.

The other two forces are electromagnetism and gravity. If you slam your hand on a table, electromagnetism is what keeps your hand from flying through the table into your lap. This force is widely credited with the success of the restaurant industry.

Gravity pulls you toward the center of the Earth, and keeps you from drifting up toward the ceiling and getting it dirty.

Incidentally, Deimos, one of the two moons of Mars, is so small ("only" two million billion kilograms), and consequently has such weak gravity, that if you were standing on it, and you jumped hard, you could easily achieve escape velocity and never land back down on the ground.

Electromagnetism is also generated by magnets, and causes metal objects to be attracted to each other. A hand-held magnet is strong enough to lift a small screwdriver off a table.

Think about what's happening with gravity in this situation. The electromagnetic force generated by the magnet is strong enough to lift the screwdriver up off the table, overcoming the force of gravity. But what's generating the gravitational force?

The whole Earth!

The Earth has a mass of six million billion billion kilograms, and yet its gravity isn't enough to overcome the magnetic force generated by a magnet whose mass is a small fraction of one kilogram.

I'm out of shape and I have a desk job, and I can overcome the gravitational force created by the mass of the entire Earth with my little finger. Gravity isn't all that impressive.

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