Physics is a quantitative science, relying on accurate measurements of fundamental properties such as time, length, mass and temperature. To ensure measurements of these properties are accurate and precise, instruments such as meter sticks, Vernier calipers, micrometer calipers, triplebeam balances and laboratory thermometers are often used. It is important to understand how to properly use these devices. With any measurement tool, the student should always try to achieve the greatest accuracy the apparatus will allow.
Meter stick. The simplest way to measure length is to use an ordinary meter stick. In the laboratory, our meter sticks are carefully calibrated in centimeters with a millimeter least count. That is, the millimeter is the smallest subdivision on the meter stick, which can be seen in Figure 1. This means the millimeter is the unit of the smallest reading that can be made without estimating.
Vernier caliper. A vernier caliper (or vernier), shown in Figure 3, is a common tool used in laboratories and industries to accurately determine the fraction part of the least count division. The vernier is convenient when measuring the length of an object, the outer diameter (OD) of a round or cylindrical object, the inner diameter (ID) of a pipe, and the depth of a hole.
The vernier consists of a main scale engraved on a fixed ruler and an auxiliary scale engraved on a moveable jaw (see Figure 3). The moveable jaw is free to slide along the length of the fixed ruler. The main scale is calibrated in centimeters with the smallest division in millimeters. The moveable auxiliary scale has 10 divisions that cover the same distance as 9 divisions on the main scale. Therefore, the length of the auxiliary scale is 9 mm. When the vernier is closed and properly zeroed (see Figure 4), the first mark (zero) on the main scale is aligned with the first mark on the auxiliary scale. The last mark on the auxiliary scale will then coincide with the 9mm mark on the main scale. A reading is made by closing the jaws on the object to be measured. Make a note of where the first mark on the auxiliary scale falls on the main scale. In Figure 5, we see that the object's length is between 1.2 cm and 1.3 cm because the first auxiliary mark is between these two values on the main scale. The last digit (tenths of a millimeter) is found by noting which line on the auxiliary scale coincides with a mark on the main scale. In our example, the last digit is 3 because the third auxiliary mark lines up with a mark on the main scale. Therefore, the length of the object is 1.23 cm.
Triplebeam balance. The triplebeam balance, or laboratory balance, measures the mass of an object by balancing the unknown mass with sliding masses of known values. The triplebeam balance is usually calibrated in grams with a least count of 0.1g. A measurement, then, can be made to 0.01g. It is important to note that laboratory balances are used to make measurements of an object's mass, not weight. (The weight of an object, as you will learn, is the product of the object's mass, m, and the acceleration due to gravity, g, or W = mg.) Before the triplebeam balance is used to make a measurement, verify that the balance is properly zeroed. Fine adjustments may be made by turning the knob under the balance pan.
Graduated cylinder. The volume of an irregularly shaped object may be determined with the use of a graduated cylinder. To do so, fill the cylinder with water or other liquid and completely submerge the object in the liquid. The volume of the object is measured by calculating the difference in the water level before and after the object was submerged. Graduated cylinders are usually calibrated in milliliters or cubic centimeters (1ml = 1cc = 1cm^{3}) but their least counts vary from 1ml to 10ml depending on the size of the vessel.
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