
Title:
0541 The Normal Force

Description:

Now, one important thing to notice is that this force of the ground pushing up on the ball

is always going to be perpendicular to the ground.

This is some sort of perpendicular force.

In fact, let's call it FN where N means normal.

Normal is just another word for perpendicular.

Before we move on, I want to point out something truly beautiful here.

We just discovered a force.

We discovered that force by having real trust in our model, F = ma.

If this is true and there really is a force downwards,

there has to be, must be, a corresponding force upwards.

We call that the normal force.

In fact, we can verify the existence of the normal force

with something as simple as a scale, like the one you might find in your bathroom.

Here you are, some person, your mass is m, and you're standing on a scale.

I don't like this picture, because people are hard to draw.

Let's simplify a bit. Here you are, standing on a scale again.

This time I've drawn you as a box.

No offense. I don't think you look like a box.

But it's just easier and we can find that drawing things this way

will actually make solving later problems much easier.

We know that gravity is pulling you downwards with a strength mg.

That mg, by the way, is what we colloquially call your weight.

The scale, of course, is pushing up with a normal force.

Now, let's think. How big is that normal force?

Is it bigger than mg, equal to mg, or less than mg?

Remember, the total or net force on an object is equal to

its mass times the object's acceleration. Choose the best answer.