Physics 101 (lab 3) Ivan Branov

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George Mason University *

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101

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Physics

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Dec 6, 2023

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Physics 101 (General Physics-1) Laboratory Exercise (3) The size of things and use of measurement instruments Your Name: Ivan Branov Lab partners name: Student ID:6468781 Date: 02/08/2022 Introduction: Physics is a quantitative experimental science and as such is largely a science of measurement. Over time, instruments of great accuracy have been devolved to help scientist make better measurements. Common laboratory measurements involve the determination of the fundamental properties of mass, length, volume density. Most people are familiar with the use of scales and rulers or meter stick. However, for more accurate and precise measurements laboratory balance and Vernier calipers or micrometer calipers are often used for smaller object measurements. In this lab, the dimensions of various objects will be measured using a meter stick, Vernier caliper, and micrometer. You will also get a chance to compare the British and metric system of units. With the use of an electric scale, the mass of some objects will be measured and from this, the density will be calculated. Objectives: The object of this lab is to (1) Learn how to use these instrument and what advantages they offer. (2) Learn how to measure small objects using Vernier calipers and micrometer calipers. (3) How to experimentally determine densities of several materials and (4) Distinguish between mass and density, and calculate % error between densities of different materials with the known densities. Equipment needed: Laboratory balance, Vernier caliper, Micrometer caliper, Meter stick, Graduated cylinder, Cylindrical metal rods, Some metal or glass sphere, Short piece of solid copper wire, Rectangular piece of metal sheets, Irregularly shaped metal objects. Theory: Using the proper instrument is extremely important for making accurate measurements of physical properties. The easiest way to measure length is to use a meter (or English yard) stick. For normal everyday measurements, a visible comparison between the object of interest and the scale is all that is needed. To make precise measurements, the scale must be very accurately made and must be read to a fraction of its smallest scale division. When an instrument is used to the limit of its precision, certain errors occur that cannot be eliminated. These errors are called random errors. When you make a series of measurements of a physical quantity, the individual results usually differ among

themselves because of the random errors involved. The best value of the quantity measured is then the average of the values obtained. The precision of measurements can usually be increased by using more accurate and complex equipment and by being careful to eliminate errors as much as possible. No matter what type of instrument you are using, you should always try to make measurements with the greatest accuracy attainable. Some of the instruments that will be using in this lab for accurate measurements are (a) electronic balance, (b) Vernier calipers and (c) micrometer calipers (a) Different types of Laboratory balance: Mechanical balance: are used to balance the weight of an unknown mass m against that of a known mass m 1 so that mg=m 1 g or m 1 =m. The mass of the unknown is then read directly in mass units. The weight W of an object is W=mg (where g=9.8 m/s 2 ) Double beam-double platform balance or equal arm balance: In this balance a set of known masses is used to balance an unknown mass A single platform triple beam balance: On a triple beam balance, the riders on the beams are used to balance the unknown mass on the platform. The common laboratory balance is calibrated in grams. In this case the least count is 0.1 gram and a reading can be estimated to 0.01 g. High form beam balance: In this balance on the left has a dial mechanism that replaces the lower mass beams. Digital balance: The balances with digital readouts are common and have the advantages of accuracy and ease of operation. However, these balances are much more delicate. Some electronic balances have auto calibration and other have key pad for calibration by the user. Most digital balances are zeroed by pressing a button and then when the material is added to the dish, the balance displaces the mass of the content alone. (b) Vernier calipers: In 1963 French instrument maker, Pierre Vernier invented the Vernier calipers in order to improve the precision of length measurements. This scale consists of two parts: A ruler with a main engraved scale and a movable jaw. The span of the lower jaw is used to measure the length and is particularly convenient for measuring the diameter of a cylindrical object. The span of the upper jaw is used to measure the distances between two surfaces, such as inside diameter of a hollow cylindrical surfaces.

The main scale is calibrated in centimeters with a millimeter least count, and the movable Vernier scale has 10 divisions on the main scale. When making a measurement with a meter stick it is necessary to estimate the fractional part of the smallest scale division (tenth of a millimeter). The function of the Vernier scale is to assist in the accurate reading of the fractional part of the scale division, thus increasing the precision. If the Vernier mark coincides with the mark on the main scale, then the Vernier mark number is the fractional part of the main scale division. However, a mark on the Vernier scale may not always lineup exactly with one in the main scale in this case we say there is a change in phase between two successive Vernier markings. (c)Micrometer calipers: Micrometer calipers commonly called mike provides for accurate measurements of small length. This instrument is particularly convenient in measuring the diameter of a thin wires and thickness of the thin sheets. The micrometer calipers consist of a moveable spindle, parallel faced jaw (Anvil) rotating thimble, engraved sleeve mounted on a solid frame and ratchet handle. The axial line on the sleeve main scale is calibrated in mm. 1 mm main scale divisions is analogous to 1$ and the thimble scale divisions as cents (0.01). One complete rotation of the thimble scale is 0.5$ and second rotation corresponds to going from $0.5 to $1.00, so two complete rotation go through 100cents, or $1.00 of the main scale. Measurements are taken by noting the position of the edge of the thimble on the main scale and the position of the reading line on the thimble scale. For example, for the drawing in the fig.(right) the mike has a reading of 5.785 mm. on the main scale is a reading of 5.000 mm plus one 0.500mm division (scale below reading line) giving 5.500 mm. Now the thimble is in the second rotation of a main scale division. The reading on the thimble scale is 0.285mm where 5 is the estimated or doubtful figure. Density measurements: The density, (rho), o ρ f a substance is defined as the mass m per volume V , i.e. = ρ m/V. This may be determined experimentally by measuring the mass and volume of a sample of a substance and calculating the ratio m/V. The volume of a regular shaped object can be calculated from length measurements; for example:

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