Objectives: Distinguish between mass and weight Convert mass and weight units Convert time units

Mass and Weight  mass – quantity of matter in an object.  gram – unit of mass in the metric system.  Defined as the mass of 1 cc of water at 4 o C.  Gram too small, so kilo gram is the base unit  Defined as the mass of 1 dm 3 of water at 4 o C.  A paper clip is about a gram  Smaller unit, the mg  About the mass of a grain of salt  Larger unit, the metric ton (= 1000 kg)

 weight – measure of the gravitational force acting on an object.  While the mass of an object does remains the same, the weight of an object changes with distance from earth (or another planet).  SI unit, the Newton (N)  About the weight of a small apple  U.S. unit, the pound (lb)  1 lb = 16 oz  1 N = lb, or 1 lb = 4.45 N

 Weight is measured with a spring scale – contains a spring that stretches in proportion to the weight of an object.  Has a pointer with a calibrated scale read directly in pounds or Newtons.  A platform balance measures mass of an object by comparing the pull of gravity of a known mass to an unknown counter- mass on a fulcrum.

 Example 1: Change 74 kg to grams.  Example 2: The weight of the intake valve of an auto engine is 0.18 lb. What is the weight in ounces? Newtons?

Time  Units based on the motion of the earth and the moon.  Revolution  Rotation  Lunar cycle  Basic unit is the second (s)  Was based on 1/86400 the average solar day.  Now defined by the frequency of radiation emitted from Cesium (Cs)

 Equivalents  1 min = 60 s  1 h = 60 min  1 day = 24 hr  1 yr = 365 days  Example 3: Change seconds to nanoseconds.