Statics: Equilibrium

A dust tray

(a)                                                                               (b)
Fig. 1-12: An application of inequilibrium

Equilibrium may also be found in several common items used in daily life. Fig. 1-12a shows a dust tray which is often used in fast food restaurants to collect rubbish from floors. When moving the dust tray between locations, one lifts the vertical handle. The tray then rotates through an angle such that the rubbish will be kept at the end of the tray as shown in Fig. 1-12.b. The rotation occurs because there is a pivot on the tray and the pivot is purposely placed at the position which will cause the tray to turn. Because the mass centre of the dust tray in its horizontal position is not in line with the handle, the tray rotates until this is the case. If the larger portion of the tray lies behind the handle, the direction of rotation is such that rubbish remains trapped during movement.