1.5 OTHER UNITS

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

oC. Gram too small, so kilo gram is the base

unit Defined as the mass of 1 dm3 of water at

4oC. 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 = 0.225 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 0.000 000 025 seconds to nanoseconds.