 The Metric System  Objectives:  1. Explain why scientists use a standard measurement system.  2. Identify SI units of measure for length, mass, volume, and density  3. Calculate volume and density

 The metric system is a system of measurement based on the number ten.  Modern scientist use a version of the metric system called the international system of units abbreviated as SI.  Scientists all over the world use SI units to measure length, volume, mass, density, temperature and time  Using SI as the standard system of measurement allows scientists to compare data and communicate with each other about their results.

 The basic unit of length in the SI system is the meter.  One meter is about the distance from the floor to a doorknob.  To measure objects smaller than a meter, scientists use the centimeter or millimeter.  One meter is equal to 100 centimeters or 1000 millimeters.

 Mass is the measure of the amount of matter an object contains.  The basic unit of mass in the SI system is the kilogram.  The mass of a wooden baseball bat is about 1 kilogram.  To measure the mass of smaller objects, you can use the gram or milligram.  One kilogram is equal to 1000 grams.  A very common tool to measure mass is the triple- beam balance.

 Volume is the amount of space an object takes up.  The basic unit of volume in SI is known as the liter (L)  One liter is equal to 1000 mL  Scientists commonly use a graduated cylinder to measure liquid volumes.  The liquid at the top of a graduated cylinder will be curved. This curve is called a meniscus.  One cubic centimeter is exactly equal to one millilter.

 The volume of a regular shaped solid can be found using this formula: Length x Width x Height.  To measure the volume of an irregular solid, you record the volume of water in a graduated cylinder.  Then, carefully place the irregular solid into the water. Record the volume of the water with the object in the water.  Subtract the volume of water alone from the volume of the water and the object.

 Density is the measure of how much mass is contained in a given volume.  The formula to solve for density is: Density = Mass/Volume  Because density is actually made up of two measurements; mass and volume an object’s density is expressed as a combination of two units.  Two common density units are grams per cubic centimeter and grams per milliliter.

 The density of a substance is the same for all samples of that substance.  For example, all samples of pure gold no matter how large or small have a density of 19.3 g/cm 3  An object will float if it is less dense than the surrounding liquid.  For example, the density of water is 1 g/cm 3. A piece of wood with a density of 0.8 g/cm 3 will float in water.

Substance Density (g/cm 3 ) Air Ice 0.9 Water 1.0 Aluminum 2.7