Lesson 1

Explore

In Try This 1 you worked with a variety of measurement tools and a variety of objects to measure. You may have discovered that some measurement tools are better suited for measuring large objects when accuracy may not be as important. However, others are better suited for measuring small objects where greater accuracy may be needed.

Suppose you measure the length of a wall using the length of your foot as a referent. As you can imagine, this method of measurement is not very accurate for a number of reasons. For example, you might not walk in a straight line, or your feet might not touch the same way each time, which would leave ample room for error. Instead, if a measuring tape is used, the length of the measurement will be more accurate, since it is a single measurement along a straight line.

It is important to recognize and choose the correct measuring device that is best suited for the required accuracy of a measuring task.

Self-Check 1

Order the following clocks from the least accurate time keeper to the most accurate time keeper. Explain your choice.

• alarm clock
  
  
  Martin Poole/Photodisc/Thinkstock
  
• hourglass
  
  
  iStockphoto/Thinkstock
  
• rusty clock
  
  
  Hemera/Thinkstock
  

Answer

In 1875, the first General Conference on Weights and Measures was held to set measurement standards. At this time, a metre was defined as the distance between two very fine marks on a bar made of an alloy that resists rusting and other changes. Copies of this bar were made and sent to laboratories in several countries of the world. Today, the standard for the metre is the distance travelled by light in a vacuum in of a second.