MEASUREMENTS, THE METRIC SYSTEM, AND DENSITY

WHY DO WE USE THE METRIC SYSTEM?  Almost all other countries are using the metric system  Other countries’ companies are refusing to buy products from the U.S. if not labeled in metric units  Scientists need a universal way to communicate data (SI Units)

Lets look at our system…  fractions of inch...  12 inches to a foot….  3 feet to a yard….  5.5 yards to a rod an...  320 rods to a mile...  43,560 sq. ft. to an acre...  16 ounces to a pound...  12 ounces to a pound...  4 quarts to a gallon...  3 teaspoons to a tablespoon…

WHAT DOES THE METRIC SYSTEM MEASURE?  The gram measures mass  A balance is used to measure mass.  The liter measures volume which is used when measuring liquids.  A graduated cylinder is used to measure volume.  The meter measures the length of an object or the distance from place to place.  A ruler or meter stick is used to measure length.  These are the base units of measurement.

Prefixes plus base units make up the metric system.

Staircase Conversions

Metric units  U.S. Customary Units

Practice Problems  500 mL = ___ L  600 g = ___ kg  8 ounce carton of milk = ___ mL  218 pounds = _____ kg

Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object. Density is the amount of matter within a certain volume.

What is Density? Density is the Mass per unit Volume WoodWaterIron 1 cm 3 1 cm 3 1 cm 3 If you take the same volume of different substances, then they will weigh different amounts g1.00 g8.00 g Q) Which has the greatest mass and therefore the most dense? IRON

DENSITY g/cm 3 Aluminium2.70 Brass8.50 Iron7.86 Wood0.50 Slate2.80 Glass2.50 Lead11.3 Marble2.70 Wax0.89

Density Formula  Density is mass divided by volume.  Density = mass/volume  The unit for mass is grams  The unit for volume is mL or cm 3  The unit for density is…  g/mL or g/ cm 3

Units for density g/cm 3 or g/ml Formula: M = mass V= volume D = density M = D x V V = M / D D = M / V

Water and Density  Since 1-gram of water has a volume of 1-mL  then the density of water =1 gram/mL.  5o-mL of water will have a mass of 50 grams  so again the density of water =1 g/mL.  A kg of water will have a volume of 1000-mL  so again the density of water =1 gram/mL.

Floating  Less dense materials will float on top of more dense materials.  Objects with a density of less than 1-g/mL will float on top of water.

Neutral Buoyancy  Objects with a density equal to the density of water will float in mid water, at what ever level you place the object.  Fish and submarines control their depth by changing their density.

Objects that Sink  Objects with a density greater than 1 g/mL will sink in water.