you can measure the density of plastic using an instrument called electronic densimeter. this densimeter give you the density measurements very easily and fast. below is few models of this instrument.
http://www.worldtesters.com/Tester_Meters/Densimeters.htm
specific gravity test
A hydrometer is commonly used to test the specific gravity of a forklift battery. This device measures the density of the electrolyte in the battery, which can provide information about the state of charge and health of the battery.
An aerometer is an instrument used to measure the mass and density of gases.
a viscometer is used to determine viscosity(density) of a liquid.
this is an instrument in the laboratory that is used to clean various kinds of test tubes.
Plectrum
Spirometer
Piano
The instrument used to test knee reflexes is a reflex hammer. The doctor will tap the tendon below the kneecap to evaluate the neurological responses and reflexes in the leg.
False. The streak test is not a test of mineral density but is used to determine the color of a mineral in powdered form by scratching it on a ceramic plate.
The first plastic bottles were used in 1947, but they didn't become widespread till the 1960s when high density polyethylene was used.
Battery capacity tester