Thames & Kosmos Physics Workshop handleiding

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Handleiding

You will also need: 1 wooden matchstick, 2 small raw potatoes (as round as possible, one

about 3 cm (1 in) thick and other about 5 cm (2 in) thick)

First, hold the smaller potato between your thumb and foreﬁnger beneath the last hole in

the small rod at the top of the potato trap model, without it touching the assembly. If the

potato is not perfectly round, turn its fat end to the boom, so that it doesn’t rotate too

much as it falls. Let it go carefully, without jerking it! Did it hit the target stick? If not, try

again. When you hit the stick, use the second matchstick to measure how deep of a hole

you made in the potato. Make a mark on the matchstick with a sharp pencil to record the

depth of the penetration of the match into the potato.

Now drop the larger potato. Measure the depth of penetration. Have you noticed

something? Exactly: the faer potato has the deeper hole.

Potatoes and Weight

The results of this ﬁrst experiment probably make complete sense to you. After all,

the faer potato is heavier. Right. But what exactly do we mean by “heavy?” If you

try to stab the matchstick into the potato with your hand, you will notice that you

need to use some force. And because the matchstick embedded itself in the potato

when it fell, there must have been force in the falling potato too.

Another name for the force of gravity is gravitational araction. Earth aracts

or pulls on all objects with its great mass. It is this force of araction that makes all

objects “heavy,” and that gives them their weight. When you hold a potato in your

hand and feel its weight, you are feeling the gravitational force of Earth, which pulls

the potato downward.

Mass Is Everything

Why does Earth aract things? First of all, there will always be a force of araction

between two bodies — that is a law of nature. The araction exerted between two

bodies is called gravitation (from Latin gravis = “heavy”). Earth is a powerfully large

body and its force of araction acts on all other bodies on or around it. It acts more

weakly on those bodies we call “light,” and more strongly on those we call “heavy.”

That is why the penetration hole was deeper in the larger potato than in the smaller

one. The strength with which Earth aracts a body depends on its mass. But what

exactly is meant by mass?

On the Moon

Let’s touch down on the moon for a lile while. We get out of the landing module

and work up the courage to take our ﬁrst step. As soon as we take it, we’re carried

along for several meters, hovering just over the surface before our foot lands. The

reason: the moon has a mass one sixth that of Earth, and a gravity weaker than

Earth’s by that same factor. Thus, we weigh six times less on the moon than we do on

Earth. But whether we are on Earth or the moon, our mass remains the same.

GAME

Who has the

best aim?

After the experiment, two or more

players can drop their potatoes onto the

spit ﬁve times each. Whoever gets the

most hits, and whoever ends up with

holes closest to one another, wins the

game. The loser has to peel and cook

the potatoes. The grand prize winner is

the one whose potato is impaled two or

more times in the same hole. The prize?

You have to think that up for yourselves.

KEYWORD:

GRAVITATION

Gravitation is a force manifested by

acceleration toward each other of two

free material particles or bodies.

KEYWORD: MASS

Mass is the property of a body that

is a measure of its inertia and that

is commonly taken as a measure of

the amount of material it contains

that causes it to have weight in a

gravitational ﬁeld.

EXPERIMENT 1: POTATO TRAP

Earth Attracts Us

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