Tel: 0741 340 199

Two Forks in Balance

You can imagine that this is like a simple pendulum where the center of mass (the ball at the end of the pendulum) swings below the pivot. If the pendulum's ball is pulled up a little, it will try to return to its most stable position with minimum po-tential energy. The pendulum will con-tinue to oscillate about the pivot point until all its kinetic energy is lost to friction and it will settle down to the position with least potential energy. In our case if you want to have a stable situation, the cen-ter of gravity of this assembly has to be below the pivot point. The pivot point is where the toothpick rests on the rim of the glass. The actual center of gravity must lie in the empty space between the two forks and below the pivot point to achieve stability.

About this experiment...

IX D class, “Mihai Eminescu” National College

`Course science can be fun.

We rock science.

Papuţa Duţu Carmen

!X D

crmn_kat@yahoo.com

Str. Mihai Em

inescu, nr. 5 Loc. Satu M

are Jud. Satu M

are Rom

ania

IX D class, “M

ihai Eminescu” N

ational College

This is an old trick to balance two forks sup-ported by a thin tooth pick. This one is quite spec-tacular when you actually see the pivot point resting

o n t h e r i m o f a g l a s s . This demonstration shows not only the concept of center of gravity but also stability.

Material list:

♦ Two metal dinner forks, preferably identical.

♦ Toothpick

♦ One glass

♦ Matches

Assemble

Stick two forks one into each other and then stick the toothpick between their teeth, so that the assembly does not move. Now put the toothpick on your finger, and try to bal-ance the above assembly on your finger. If the angle of the forks is suitable, you should find a point on the toothpick that you can bal-ance the forks. Mark this point. Now try to balance the assembly on the rim of the glass. It should bal-ance at about the marked point. (see the first and sec-ond picture)

To do

Light the toothpick at the free end and watch the toothpick burn away (third picture). The burning will stop once it hits the glass rim, but the fork assembly continues to be balanced at that point. (last picture)

Physics explanations Center of Gravity of any object is the point about which you can balance the object as if

all the masses were concentrated or gathered at this point., regardless the shape of the object. In a uniform gravita-tional field, the center of gravity and cen-ter of mass are located at the same point. The center of gravity does not have to be on the object, it can be in the open space. For instance, the center of gravity of this fork assembly is in between the forks in the empty space. How do we make it sta-ble?

It will be stable if the center of gravity lies below the pivot point. If the center of gravity is above the pivot point, even a slight disturbance will pull it off balance.

Str. Mihai Eminescu, nr. 5 Loc. Satu Mare Jud. Satu Mare Romania

Phone: 0261 768 855 Fax: 0261 768 855 E-mail: crmn_kat@yahoo.com

IX D class, “Mihai Eminescu” National College

Center of Gravity of Two Forks

First picture

Third picture