Why doesn't a spinner want to fall?

It’s much more fun to study the laws of physics with a spin­ner in your hand!

Safe­ty pre­cau­tions

  • Only un­der adult su­per­vi­sion!
  • Be care­ful when us­ing the drill!


  • spin­ner;
  • screw­driv­er;
  • dow­el;
  • screw;
  • string;
  • straw;
  • drill.

Step-by-step in­struc­tions

Re­move the spin­ner’s plas­tic lin­ing. In­sert a screw into the hole in the cen­ter of the spin­ner and tight­en it. Make a loop in the string. Set the spin­ner in mo­tion (we used a drill to in­crease the speed of the spin) and hook the end of the screw on the loop or bal­ance it on a straw. Let it spin, and some­thing in­cred­i­ble will hap­pen! In­stead of fall­ing, the spin­ner will con­tin­ue to ro­tate ver­ti­cal­ly, and will also start to re­volve around the ful­crum! You might ex­claim: “This is im­pos­si­ble!” – and a physi­cist would an­swer, “No, this is just pre­ces­sion.”

Process de­scrip­tion

An­gu­lar mo­men­tum char­ac­ter­izes ro­ta­tion­al mo­tion the same way that or­di­nary mo­men­tum char­ac­ter­izes trans­la­tion­al mo­tion. This an­gu­lar mo­men­tum of a body is de­ter­mined rel­a­tive to a se­lect­ed point of ref­er­ence, and de­pends on the body's mass and ve­loc­i­ty, as well as on the dis­tance be­tween the body and the ref­er­ence point. The ro­tat­ing spin­ner has a large an­gu­lar mo­men­tum rel­a­tive to its own axis of ro­ta­tion. The ac­cel­er­a­tion of the ro­tat­ing spin­ner doesn't co­in­cide with the di­rec­tion of grav­i­ty due to the pe­cu­liar­i­ties of the law of change of an­gu­lar mo­men­tum. More­over, the force of grav­i­ty changes only the di­rec­tion of the an­gu­lar mo­men­tum, with­out chang­ing its val­ue. Un­der the in­flu­ence of grav­i­ty, the spin­ner starts spin­ning around the ful­crum in­stead of fall­ing over.This ad­di­tion­al ro­ta­tion is called pre­ces­sion. The ro­tat­ing spin­ner is a sim­ple form of a gy­ro­scope, a de­vice that al­lows you to de­ter­mine the spa­tial ori­en­ta­tion of a sup­port. Gy­ro­scopes are wide­ly used in nav­i­ga­tion and sta­bi­liza­tion sys­tems. Even our plan­et Earth is a gi­ant top, the axis of ro­ta­tion of which is in­clined rel­a­tive to its plane of or­bit. The Moon and the Sun cre­ate tidal forces which cre­ate a ro­ta­tion­al mo­ment. Un­der the in­flu­ence of these forces, the Earth's axis slow­ly pre­cess­es, re­turn­ing to any set “start­ing point” ap­prox­i­mate­ly once ev­ery 26,000 years.