# CENTRIPETAL FORCES

See these children flying around ? They are safe…

The chains keep the seats in place while they go around and around…

How come?

++++++++++++++++++

Look at the sketch.

The ball on her string follows a perfect circle.

The string pulls on the ball with a force, called CENTRIPETAL force.

(“Centri…” means center and “petal…” means to seek: the force on the ball is towards the center)

The colored arrow shows the speed of the ball around the circle…

But when you let go, the ball flies away in a straight line.

You can try it out with a tennis ball or any soft piece, a little bag with sand will do.

+++++++++++++

You have to tug on the string and that force is called CENTRIFUGAL force.

You already know what “centri…” means and “fugal” comes from “to flee”

So hold on if you want the ball to go around in a circle

Let go and the ball no longer goes in a circle but flies away, straight…

For the ball,

ONLY THE CENTRIPETAL FORCE MATTERS,

while you swing it around!

+++++++++++++++++

Figure Skating …

The male skater holds on to his partner and she goes around in a circle because of the centripetal force on her body.

WOW

++++++++++++++++

CENTRIPETAL  TOY,

you move the bowl in small circles while you hold it at the handle with the bowl horizontal.

The marble starts running around at a  high-speed.

The bowl keeps it in a circle and presses on it with the CENTRIPETAL  force.

BUT, the marble tries to go faster in a larger circle and therefore climbs up the wall of the bowl!

YOU

stop it from flying out off the bowl when it wants to go too fast,

it hits the rim we made of red tape.

STOP

the motion of your hand and the marble slows down

and rolls into the bottom of the bowl,

because GRAVITY is pulling it down.

++++++++++++++

If you just hold it there the marble will sit quietly at the bottom of the bowl,

it can not go anywhere else, right?

Then try again… Keep experimenting.

As long as you hold the bowl horizontal, you can spin the marble as fast as you can!

++++++++++++++++++++

Let’s go in ORBIT…

EARTH moves around the SUN once per year as long as we can imagine…

The sun is very BIG  and our earth is small

(The sun is about 100x as wide as earth and 1,000,000 as big in volume)

(but earth is all we have as our space to live, save it! )

In the sketch the sun at the center is   NOT the right size or scale:

What keeps the earth going around the sun like somebody in a merry-go-around?

The centripetal force of GRAVITATION.

Notice: where earth is in June, September, December and March,

it takes one year for earth to go around the sun once.

++++++++++++++++

But we are not alone…

Here is our own moon circling earth,

the blue line is just to show she goes around our earth.

The CENTRIPETAL GRAVITATIONAL  force of the earth keeps the moon in orbit.

You can see the moon rising early in the evening.

Like here, across the Red Sea, but you can ALSO see her from your window when the night is clear.

+++++++++++++++++

But there is still more and more and more…

The sun and its planets all in orbit around the sun.

See planet earth among the planets?

And all that is part of this… the

# Galaxy

And more and more… all held together by the gravitational centripetal forces!

Sorry I am getting a little dizzy, what about you?

Phew…

Let’s make our Centripetal Force Toy.