Die prentjie aan die regterkant wys 'n regterkantste fietstrap. Die rooi pyle wys die '''skynbare''' draairigting van die trap-as ten opsigte van die traparm agv die draaiweerstand van die trap-as. Dus, wanneer die fiets normaalweg getrap word, lyk dit of die trap sal neig om los te draai. Hoekom dan het die regterkantste trap 'n regshandige skroefdraad?
Die antwoord lê in meganiese presessie (kyk prentjie aan die linkerkant).
[[Lêer:Rotasie_van_as_in_gat.PNG|thumb||links|250px400px|Meganiese presessie: DieWanneer groendie roterendedaar pyl'n isantikloksgewyse die rigtingkrag waarinop die binneste as (blouuitgeoefen dele)word, gedraaisal worddit agvveroorsaak dat die trap-as sein draaiweerstand.'n Diekloksgewyse blou delerigting stelbinne die trap-asgroter vooris diegat beweeg.]]
- the process of a round part (in blue) in a round hole (in red) rolling in the direction opposite to the rotational direction of the applied radial force. (The applied radial force is depicted by the green arrow. The arrow's counterclockwise rotation depicts the direction of precession, while the direction of rotation is shown by the clockwise rotation of the blue square. The center of the blue square is traversing counterclockwise along a small circle, the orbit, of diameter equal to the difference of the diameters of the red circle and the blue circle, even though the blue square rotates clockwise). If the blue circle has a diameter ''d ''and the red circle a
diameter '' d + δ. ''The instant the green arrow is pointing downwards, the blue circle is pressed against the red circle at the bottom (point ''A ''on the blue circle). The force rotating counterclockwise causes the blue circle to roll around the red circle clockwise. When it has rolled a distance '' πd'', the circumference of the blue circle, point '' A'' again touches the red circle. Since the circumference of the red circle is π(''d'' + δ), point '' A'' touches the red circle a distance πδ clockwise from the bottom.]]
