# Gayaza High School/Departments/Departments/Physics/O'Level Resources/Measurements

Units

Measuring an object means comparing it to a selected unit (such as a meter) and expressing it as a multiple or fraction of that unit (e.g., 2 meters, 1/2 meter, 1.3 meters). Accuracy of measurement refers to the discrepancy between the true or actual value and the result obtained by measuring. Precision refers to the agreement among repeated measures of the same quantity or object. To understand the differ­ence between precision and accuracy, suppose you use a meter stick to measure the length of a table and get these results: 2.31 m, 2.32 m, 2.30 m. The spread of the mea­surements is only 0.02 m, which indicates good precision, If, however, the meter stick itself were not graduated correctly, and was Actually 1.04 meters In length, then the marks on the stick would be slightly farther apart than they should be, Conseqently

Dimensions (units)/ measurement, accuracy, precision.

Material*'. None required.

Principles and Procedures:
We use units every day, often without even realizing it. In the k 1.1 foments that follow, you will find a wide variety of interesting facts, but each is missing a crucial piece of information—the dimensions. All the statements are meaningless until you supply the appropriate units.
Activity
On the basis of your experi­ences, try to determine the appropriate units from the list provided. Units may be used more than once or not at all.

Possible Units for Questions in (a)-(t)

 bushels centimeters days degrees Celsius degrees Fahrenheit feet grams hours inches kilocalories kilometers kilowatt hours meters miles miles per hour milligrams minutes percent persons pounds seconds square miles stories terms yards

a)   The world's tallest building (Sears Tower in Chicago) is 110 _; high.

(c)    The Nile is the world's longest river. It is 4,180 __ long.

(d)   The Amazon River in South America is __ 6,296 long.

(e)    Alaska has the lowest recorded temperature of any state. In 1981 the temper­ature was recorded at -81 __.

(g)   The world-record rainfall occurred in Cherrapunji, India, where 1,042 _ of

rain fell in one year.

(j)    Big fish don't always get away: In 1953 A. C. Glassel caught a marlin that weighed in at 1,560__.

(k)   The dimensions of a professional basketball court are 94_ by 50_.

Unit One: Measurement
(n)   The temperature of the core of the Earth is estimated to be 11,000__.
(o)   The world's fastest aircraft was the Lockheed SR-71 A/B Blackbird. Before

being retired, it clocked a record speed of 2,193.67__.
(p)   Iowa is the biggest corn producer in the country. Each year it averages over

1.6 million ___.

(q)   One large cooked egg yields an average of 6 __ fat and 274__ cholesterol.
(r)    A 16-year-old male requires an average of 2,800 __ of energy per day while

an average 16-year-old female requires only 2,100__.
(s)    Before its breakup, the world's largest country was the Union of Soviet

Socialist Republics. It had an area of 8,649,496 ___, compared to only

3,615,105 ____ for the Uganda.
(t)    The United States produces and consumes more electric energy than any

other nation. Each year she produces over 2,500 billion __ while the entire

nation of China produces only about 400 billion __.

# Reflection

 (1)Why is it essential that all measurements be accompanied by appropriate units? (2)    When you measure an object with a measuring instrument such as a ruler, there is always some uncertainty in the measurement. Explain. (3)    Distinguish between accuracy and precision in a measurement. (4)    Give an example of how measurements may have high precision and yet have low accuracy.