Sometimes it's hard to imagine how things move on Earth.  There is so much going on!  People walking, cars driving, clouds floating, cats running, rocks falling.  It can be a lot to take in.  So for this next lesson I am going to erase it all.  Wshh, wshh, wsssshhhhhhhhh . . . 

There.  Now you and I are standing in an empty world.  We can look at just one part of motion without anything else bugging us.

Your eyes are in your head.  They see how things move, as they come closer to you and as they move farther away.  When we watch things move, we need a point that does not move so we can see how far the thing moves.  A reference point is a fixed place from where you can observe movement.  Watch me run far away.  Now watch me run back.  It would be very hard to tell how much I had moved if you were running around too.  For this next part, I will draw a skateboard for myself.  Oh, you want to ride the skateboard?  Be my guest.  I guess I'll just stand here.

It's a simple question. Where are the brakes on this thing?

You ride every which way on the skateboard, going in circles, doing tricks.  As you ride around, you move from place to place.  When we talk about where something is, we are talking about its position.  Position means location, or where you can find something.  As you move from place to place, we can say you change your position.  It's good to know where you are just in case you are on train tracks and a train is coming.  This would be a good time to change your position.  Or say you are lost in the woods.  Knowing where you are can help you find your way home.  But we do not need to worry about this in the blank world we created.  Just look around and look for the one thing out here.  That will be me.  Or the skateboard that got away from us.

Do you know what time it is when you see this coming? Time to change position.

It's time for you to go crazy on that skateboard.  Now I will be the reference point.  I will stand still here and watch you move.  First, ride as far away as you can.  Second, ride back back.  In relation is how something's position compares to our reference point.  If you ride far away, you are far away in relation to me.  This helps us tell how fast something is moving or how far it has moved, compared to where it started.  You can be near.  You can be far.  Or you can be doing a flip over my head.  Just be careful with my head.  It would take a long time to draw a hospital.

OK, so maybe that wasn't ALL the way over your head.

It's a lot easier to watch how things move when we erase everything else.  When talking about how things move, you will always want a reference point, or one point that holds still.  If you know the position of the thing that moves, then you can know where it is in relation to that point that holds still.  I did not move, so I could see all of your great skateboard tricks.  That worked better than running around myself and making the space between us go really crazy.  Speaking of really crazy . . . I guess we should get back to the real world now.  Now if you will excuse me, I have got a lot of drawing to do.


Study Physics.  "Lesson 9: Relative Motion and Frames of Reference"  Study Physics, 2011.  <>