- DENSITY DEFINED:
Density is defined as mass per unit volume (or mass divided by volume).
It is always measured in units of mass (such as grams) divided by units of volume (such as cubic centimeters or milliLiters).
NOTE: A milliliter (mL) is the same as a cubic centimeter (cm3).
NOTE: At 4oC, the density of water is exactly 1.00 g/mL or 1.00 g/cm3
- Measuring volume:
For a rectangular solid, volume = Length x Width x Height; cm x cm x cm = cm3
For an irregular object, the volume is best determined by displacement:
- Fill a container full to the brim with water, then immerse the object.
The object will displace an amount of water
equal to its volume, so measure the overflow to determine its volume.
- FLOATING AND SINKING:
Place a solid object in a liquid.
- Objects with a density higher than the density of the liquid will sink.
- Objects with a lower density than the liquid will float. TIDBIT: The mass of the entire object
will equal the mass of the water displaced by the submerged part of the object, so an object with a density of 0.5 g/mL
will float half submerged and half above the surface, while an iceberg (density close to 0.9 g/mL) will float with 90% of its mass
submerged and only 10% ("the tip of the iceberg") showing above the surface.
-
- SAMPLE PROBLEMS:
Find the density of an object 2.0 cm x 3.1 cm x 3.7 cm with a mass of 16 g. Here's how:
| 2.0 cm x 3.1 cm x 3.7 cm = 2.0 x 3.1 x 3.7 cm x cm x cm = 22.94 cm3
| | 16 g / 22.94 cm3 = 0.69747 g / cm3 = 0.70 g / cm3
| | Notice that the final answer was rounded to two significant figures because all given units were in two sig. figs.
|
Find the volume of an object if its mass is 4.739 g and its density is 3.8 g/cm3
| 4.739 g x
| _ 1 cm3 _
3.8 g
| = _ 4.739 x 1 g x cm3 _
3.8 g
| | = 1.2 cm3 to 2 sig. figs. (because the density had only 2 sig. figs.)
| | Notice that the density fraction was inverted (1 cm3 per 3.8 grams) so that grams (g) could cancel in both numerator and denominator.
|
|