Amazing balancing fork trick

Safe­ty pre­cau­tions

Warn­ing! Only un­der adult su­per­vi­sion.

Equip­ment

• two forks;
• two tooth­picks;
• cork.

Step-by-step in­struc­tions

In­ter­twine the tines of two forks and in­sert a tooth­pick be­tween them. In­sert a sec­ond tooth­pick into a cork and set the con­struc­tion on the tooth­pick, es­tab­lish­ing a ful­crum for bal­ance. Sur­pris­ing­ly, this bal­ance will be sta­ble! You can even make the forks ro­tate around the sup­port.

Process de­scrip­tion

A body is in equi­lib­ri­um if all the forces that tend to move or ro­tate it (e.g. grav­i­ty and sup­port re­ac­tion force) are com­pen­sat­ed. When talk­ing about the bal­ance of our con­struc­tion, we must con­sid­er not only the val­ue of the forces act­ing on it, but also their points of ap­pli­ca­tion. Grav­i­ty acts on each part of the con­struc­tion, but we can con­sid­er that it ap­plies to the ob­ject’s cen­ter of mass. The po­si­tion of the cen­ter of mass of a com­pos­ite body de­pends on the rel­a­tive lo­ca­tion and mass­es of its parts, and may even be lo­cat­ed out­side of the body, as in our con­struc­tion. If the con­struc­tion is to stay bal­anced as it rests on the sup­port, its cen­ter of mass must be on the same ver­ti­cal line as the ful­crum. But that’s not all! It’s not enough to ob­tain bal­ance: it must be sta­ble! For the con­struc­tion to be sta­ble, it must be able to re­turn from small de­vi­a­tions from the po­si­tion of equi­lib­ri­um, for ex­am­ple, when we gen­tly strike one of the forks. For a body rest­ing on one point, this means that the cen­ter of mass must lie be­low the ful­crum as well as on the same ver­ti­cal line with it. The com­plex shape of our con­struc­tion ful­fills both of these con­di­tions.

Find even more ex­cit­ing ex­per­i­ments in the MEL Physics sub­scrip­tion!