measuring length by the handful the english units that we use in the united states developed over a...
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Measuring Length by the HandfulThe English units that we use in the United States developed over a long period of time. For example, the hand was devised in ancient times as a unit of length. It was defined as the length of a
person’s hand from the little finger to the thumb. Today the height of horses is still measured in hands, but the definition of a hand is standardized at 4 inches or 10.16 centimeters. 1. Why did the hand produce unreliable measurements before it was standardized? 2. Measure the height of your desk in hands. Compare your results with other
classmates. How do the results vary?
Starter 9/14
MEASUREMENT
• Measurements must have a number and unit to make sense 5 cm.
• Scientists use the SI system (SI = METRIC)
UNITS• Two types : base units and
derived units 1. Base unit – basic, simpleEx. meter, liter, gram, seconds
** add prefixes to make larger or smaller
millisecond, kilogram
Base Units :Length – meters (m)Mass – gram (g)Time – seconds (s)Volume – liter (L)
• Kilo k 1,000 • hecto h 100• deca da 10• base: 1• deci d 0.1• centi c 0.01• milli m 0.001
PREFIX Symbol multiplier
2. Derived units – combining different units using math
Speed = distance unittime unit
meters per second or (m/s)
Precision
• Precision – an EXACT measurement–Ex. Digital clocks tell the exact
time–Ex. You sit in only one specific
seat at the Phillies game.
Accuracy• Accuracy- measurement that
is CLOSE to the actual number. –It’s consistent, but not exact.–Ex. Same ball park, different
seat each game–Ex. Setting a clock – keeps time
but may not be the precise time
Starter 9/15
• Look around your seat and find 2 items that are 5 mm in length
• Find 2 items that are 3 cm in length.
Significant Figures
• Significant Figures – all the digits of a measurement that are KNOWN. –More digits = more precise–Track time = 7.8 s or 7.778 s
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