Kids' Astronomy: Movement and Distance

We started the class in a state of high excitement: the younger kids had not been in my class before, but had heard a lot from the older siblings.  We started out outside to burn off some of that energy!

 I told the kids to move in as many ways and in as many directions as they could think of, but they had to stop moving when I yelled "Freeze!"

After a few rounds of this, I told the kids that they were still moving. They were moving 700 mph west.  The older kids figured it out, first: they were moving because the Earth was spinning.

I explained that at the equator, they would be moving 1000 mph, and I took out a globe and showed them (with clay dots) how different latitudes traveled at different speeds (and that every step you took south, increased your speed!).

But how else were they moving?  Around the sun at 19 miles per second! But the sun is also moving, spinning and orbiting the Milky Way at 514,000 mph. We had to try it!

I was the sun and the kids tried orbiting (then spinning and orbiting) me as I moved.  It was really very silly! 

And, of course, the galaxy is moving, too.  In fact, if you add up all of our movement, relative to the center of the universe, we are moving at a mind boggling 805,000 miles...per second!

To look at how everything is moving relative to everything else, I had them draw clusters of dots on balloons, then inflate the balloons.  It's a good model for how everything in the universe is moving away from everything else.

So, the first point is that we re always moving, and moving quite quickly.

The second point is that things are really far away.

I showed the kids a standard picture of the solar system, and asked them what was wrong with the picture.

The planets and sun aren't sized correctly.

They also aren't spaced correctly.

At all.

I took a 20 sided die (the size of a grape) and had one lucky kid stand on our street corner.  That was the Earth.  Another kid held a pea, and stood a foot away.  That was the moon, correctly sized and spaced.  The sun, in this scale, is a 6 foot sphere.  I have a son who is 6 feet tall (but not wide), so Mxyl was our sun!  But where would he be, if the earth was grape sized?

This is the picture he took from the correct distance, a tenth of a mile away.  It was perfect!  Before he left, we set the "Earth" on the ground next to him as a size comparison.  Now we could see how small he looked away over there!

And the rest of the solar system?  At this scale, Jupiter (grapefruit sized) would be half a mile off, and Neptune (lemon sized would be 3 miles away.  The entire solar system, including the kuiper belt and the Oort cloud would take, at this scale, a jaw dropping 10,000 miles!

Which is why you rarely see an accurately scaled model of the solar system.  Although I did make one for this class: It's a black piece of construction paper with the tiniest pin prick I could make at the center.

But why are the things in the solar system moving?

Primarily, it's gravity, and gravity is a side effect of mass.  So how do you explain mass?  They need to understand volume, mass and weight.  If you don't explain volume at the same time as the others, the kids get confused between size and mass.

I have them reach as far as they can reach.  Volume is the amount of space you take up.  I put my hand in a bowl of water so they could see how my hand took up space and moved the water away. Naturally, they all wanted to try.

scale and balance

What weighs more, a pound of feathers or a pound of lead?  They have the same mass, but very different volumes!  Mass is how much stuff there is in you.   I had them jump and feel the mass of their bodies as they moved.

Then I used my primary balance to show mass another way.  As long as there was the same amount of stuff (the same mass) on both sides of the balance (in this case, baby teddy bears), it was steady.  That's the same if it's on the moon, or Jupiter, or here on Earth.  This mass of 5 equal bears will always equal the mass of 5 equal bears (about 28 grams).  Mass is measured on a balance

Weight is measured on a scale: a scale just measures how far it's pushed down.  Because gravity is relatively constant on Earth, the same amount of mass pushes down the same amount on the scale here.  But it would push down more on a larger planet, and less on a smaller one.

Just like the more magnets you have, the more magnetic pull you have (I used a bunch of magnets), the more mass you have, the more gravitational pull you have.  I "pulled" a kid in, and then, since we had increased in mass, we pulled a few more in, and so on.

Then it was back outside to look at orbiting bodies.  Zorg used his foxtail ball to demonstrate that an object in orbit will move away in a straight line as soon as whatever force keeping it in orbit is released.

Lastly, we looked at the effect of friction on orbits.

We rolled two marbles around in identical cake pans with one lined with construction paper.  The one with the paper slowed faster because of the friction with the paper.  Next time, I'd line it with fabric to make a larger difference between the two.

And then it was time to go!