Quiz 17-1: Decimal Addition Assessment
- Due No due date
- Points 3.75
- Questions 15
- Time Limit None
- Allowed Attempts 2
Instructions
DECIMAL ADDITION ASSESSMENT
As mentioned in the module overview, you are going to be learning about precision measurement tools in this module. The first one we'll discuss is the micrometer, however, in order to use a micrometer, you need to be fluent with decimal addition, since determining what a micrometer measurement is requires some math.
The Micrometer
Objectives: Students will familiarize themselves with the micrometer and accurately read measurements.
Directions: Go over the information and take the open-book quiz.
What is a Micrometer?
A micrometer is a measuring device that can measure very small amounts. A machinist would use a micrometer to make sure a part meets the tolerance for a particular product.
What is a tolerance? Let's say you're making a block that is supposed to be a 1" cube. It's very hard to get anything to be the exact size listed, so an engineer will give an acceptable range of sizes the block could be. For example, the size could be 1.000 +/- 0.005, meaning the block is good as long as it's within the range of 1" plus 5 thousandths to minus 5 thousandths of an inch. (0.995"-1.005")
You will be using an external micrometer that has markings for the inch system of measurement. It can measure up to one thousandth of an inch.
Here is a chart representing the value of each number left and right of the decimal point.
Parts of a Micrometer
Shown in Figure 1 below is a picture of a micrometer with the four main parts or areas identified. A micrometer will be needed for the next part; get your micrometer at this time.
Look at the picture and the micrometer that you have. You should be able to quickly identify measurements and the parts of the micrometer that are needed to take the measurements. Hold the frame of the micrometer in your left hand. Turn the ratchet on the thimble with your right hand. This will move the thimble up and down the barrel, which will move the spindle in or out. Try to remember what each section of the micrometer is called--you may be quizzed on this later.
Always use the ratchet (sometimes there is a friction screw instead of a ratchet) to close the spindles on an object. Otherwise, incorrect measurements will result and the tool could be damaged. There is also a locking lever which fixes the position of the thimble and right-hand measuring rod. The micrometer is a precision instrument and should be treated with care. It should never be forced. Be careful not to drop it.
Look at Figure 1 and then at the micrometer that you have. Identify the marks on the barrel of the micrometer. Each mark on the barrel is equal to 0.025" (twenty-five thousandths). Each line on the barrel with a number above it represents 0. 100" ( one hundred thousandths). The number "2" is 0.200 (two hundred thousandths), and the number "3" is 0.300 ( three hundred thousandths).
Next, look at Figure 2 and the micrometer that you have. Identify the marks on the thimble ( sometimes called a sleeve). Each of the marks on the thimble is equal to 0.001. The marks on the thimble go around the barrel. The mark that is read will line up with the index line. In figure 2, the ten lines up with the index line. It is written and read as 0.010 (ten-thousandths).
Turn the thimble and find the number 20. Using that as a reference point, continue turning the thimble until you come to the number 20 again. Notice that either more or less (depending on the direction that you turned the thimble) of the barrel has been exposed. The combination of numbers are used to determine the measurement. Consequently, we need to review your addition and subtraction skills.
Math Review
You must be able to accurately add and subtract decimal numbers, so we will have a quick review. When adding or subtracting decimals, write the problem in a stacked up fashion and keep the decimals in line. For example, the problem 0.500 + 0.034 + 0.003 = would be written as:
Work the following problems. You must get 12 of 15 problems correct to continue. The instructor will provide a calculator with which you must check your own work. Write down the correct answers by the ones you missed.