But again, that's really not the case.

If you take these two tables.

And you can use a ruler if you've got one, to make these measurements and

convince yourself.

Or you can look on the website.

I'll say a little bit more about the website

later on which I'm going to invite you to explore.

Yous'l lee that these two sets of dimensions are exactly the same.

When you rotate this table 90 degrees,

the length and width are the same as the length and width here.

So again, in geometry, wow, something

weird is going on, and what is that?

Let's take a look at angles, another, angles that's,

in addition to sort of length and width, angles is a simple aspect of geometry that

we all learned about in grade school or junior high school.

And here are examples of the four angles that look very different.

This angle looks oblique or obtuse.

This angle looks acute.

This angle looks, more or less like a 90 degree angle.

And this angle looks different from all the rest.

So here are four examples of angles that look radically different from each other.

Well, it turns out that they are all actually 90 degree angles.

And you can, again, take a coat hanger,

bend it into a 90 degree angle, hold it in different positions.

And you'll see that you can It's not something I cooked up for

the purposes of the course.

You'll see that this is easily demonstrated to yourself or your friends.

These are all 90 degree angles,

even though they look very different.

So, this also applies to motion.

And here what you're going to see, you don't see anything right now, but

you're going to see a line moving from left to right across the screen.

And then we're going to take the same line, move it across the screen and

we're just going to look at it, instead of just looking at it in the full screen,

we're going to look at it through a peephole, through an aperture.

And you'll see that the perception of the speed and the direction.

They both change.

Speed is more subtle, but it's very obvious that the direction is changing.

And let me show you that.

So here is the line moving across the screen from left to right.

Now we see exactly the same line moving left to right, but

we see it moving through a peephole.

And you saw the direction of the line change

from that direction to this direction.

Well, again, that's not a small change.

That's a change of 30 degrees or so.