Gravity pulls things together. So why doesn’t the Earth crash into the Sun…and the Moon into the Earth?

This may be one of those questions you’ve asked an elementary, middle-school, high-school, and/or college teacher about…and the answer, if you got one, always seemed a little muddy or confused. Basically, I was never given a good answer either. It took two years of college mathematics and physics before I understood it on my own. As always, I’m going to try and do better here.

Let’s start with what we know: The Earth IS moving around the sun right now. So, the entire Earth as one object has a speed and a direction.


I will try and post some of the recordings I do when I think they are worth listening to…so here is me drumming over the song, “Dancing in the Moonlight,” by King Harvest.

Well, is it?

If I am holding a bowling ball on the Moon and I decide to shake it left and right. Is that easier than it would be here on Earth…?

First, if I shook a bowling ball left and right on Earth that would be pretty hard. Does that have anything to do with the Earth’s gravity? No, it doesn’t. If you took the bowling ball and laid it on a flat table that was really, really slick. Then you don’t have to worry about overcoming any gravity at all. The ball is being held up by the table. Now, try and slide it back and forth on the table. It’s STILL pretty hard…without any gravity.

On the Moon if you threw the ball up in the air it would be easier to throw. It’s like jumping on the Moon. We’ve all seen that. So, left, right, up, down, it’s all the same, right? It’s easier to jump on the Moon because you weigh less so does that mean it’s also easier to move left and right?


Do you remember a teacher saying there was an important difference between mass and weight? You probably weren’t talking about shaking balls on the Moon. Instead, it was more likely part of a long, forgettable, and almost useless list of barely connected “scientific formulas”.

How are mass and weight different?

Your weight is how hard the Earth pulls on you. Your mass is how much “stuff you have”. On the Earth and the Moon it’s harder to pick up two rocks than it is to pick up one rock. That’s because two rocks have twice the mass as one rock. Finally, gravity, the cause of weight, only pulls down. If you are sitting on a flat chair on a flat floor gravity will never push you off the chair.

The Moon’s gravity pulls down less than the Earth’s gravity. But, even with no gravity, like in deep space, you still need a push to get moving and a push to stop. This push isn’t to overcome gravity…there is none! It’s to overcome the mass. Mass resists changes to it’s speed or direction. That idea is called things like inertia, momentum, and work. And mass doesn’t change when you move to another planet. Two rocks on Earth is still…well…TWO rocks on the Moon…

You can feel the difference by shaking your own hand.

First, shake your hand up and down. It is harder to shake up than it is to shake down, obviously. Now, shake it left to right. It doesn’t matter. It’s just has difficult to shake left as it is to shake right. When you shake your hand up and down you are feeling the effects of gravity on the weight of your hand. When you shake your hand left and right you feel how hard it is to move the mass of your hand.

So, shaking something left and right basically doesn’t have anything to do with what planet you are on…or not on. The only thing that matters is how much stuff you are shaking, and on the Moon or on Earth, for a human of average strength, a bowling ball…is a lot of stuff to be shaking.

Inspiring Trails

This image was startling to me when I first saw it. Now that I have a slightly better idea of what is going on in the picture…it’s even more stunning. These are the trails left by very small objects traveling at very fast speeds at CERN. At first it may seem hopelessly complicated, but only a few simple ideas can make some satisfying sense of this image.

First, notice there are some almost straight lines. These are neutral objects flying through the image. Things that are neutral have no charge. Just like a plain rock is not affected by a magnet, a neutral object is barely affected by magnets. In this image you can imagine that there is a huge magnet behind the screen. As these neutral objects fly past the magnet they are hardly moved.

But there is more than just straight lines in this image. It turns out neutral objects are really made up of little charged parts. If you have charge you are not neutral and you ARE affected by magnets. So what we are seeing is BIG neutral objects coming apart into much, much smaller charged parts. These small parts try and go in circles because of the magnet behind the screen.

Why they try to move in circles and why those circles inevitably fall inwards is for another post and another picture.

American Weight Gain

I took this slide show from a talk I had seen on the internet. I just wanted to make a cleaner presentation for it because I think it makes a great argument, visually.


Another collection I put together. Enjoy.

This is a segment I edited of Christopher Hitchens addressing what should be the real focus with Afghanistan.