Grades 3–5 · Materials & Matter
How does a sieve separate a mixture?
A sieve separates some mixtures by using openings of a chosen size. In the ideal drawing, a sphere smaller than an opening passes through, while a wider sphere stays above. The catch tray collects what passes so neither output group is lost.
In the diagramSeparate by size; keep every componentGiven mixture: six 1 mm + four 3 mm spheres2 mm openingsAbove: 4 • below: 6 • total: 10Ideal spheres; schematic is not to scale.
The mixture contains six spheres with a diameter of 1 millimeter and four with a diameter of 3 millimeters. Diameter is the distance across a sphere. The initial sieve openings are 2 millimeters wide, between those two sizes.
The six small spheres fit through to the tray. The four large ones remain above. Adding the two groups still gives ten spheres: the sieve has separated components rather than destroyed them. It has not dissolved them or made a new substance.
With 4-millimeter openings, both sizes fit through, so that sieve does not separate these two groups. Real particle shapes and clogging can complicate the process. This drawing uses stated sizes and ideal spheres to make the size comparison clear.
About this explanation
Starting knowledge: Compare millimeter lengths and add the counts of two groups without changing their identity.
Sources
- U.S. Geological Survey — Sieving Sediment
- U.S. Geological Survey — USGS East-Coast Sediment Analysis: Laboratory Procedures