Physical Sciences

Experiment 1

MEASUREMENTS

 

NAME:___________________________________ SECTION:___________ DATE:____________

 

INTRODUCTION:

 

All experiments to be performed in this laboratory require one or more measurements. A measurement is defined as the ratio of the magnitude (how much) of any quantity to a standard value. The magnitude is first determined by comparing the unknown quantity with the standard using some device and then the comparison is expressed as a number. A number representing the magnitude is not sufficient to express the measurement. A unit of measure must also be assigned to the number. To record a person's height as "64" is meaningless. We must record it as "64 inches". All measurements, therefore, must be recorded as a number and a unit of measure.

 

Many devices (rulers, balances, clocks, speedometers, thermometers, voltometers, oscilloscopes, spectrometers, etc.) are used to make measurements. The information obtained from these instruments must be recorded and evaluated in order to obtain an understanding of the physical quantity. Such terms as least count, significant figures, precision, accuracy and percent error must be learned and used.

 

OBJECTIVES:

 

To develop your understanding of various measuring devices. Those which will be used in this session include devices for measuring length, mass, volume and time. Methods and techniques for efficiently using and interpreting these devices will also be discussed.

 

APPARATUS:

 

Meter stick, balance, stop watch, graduated cylinder and wooden blocks

 

PROCEDURE:

 

1.                    The least count is the smallest subdivision marked on a measuring device. It is the smallest reading that can be made with the device without guessing. Determine the least count for the devices listed in TABLE 1.1. Record the numerical value for the least count and the corresponding unit of measurement.

 

 

 

 

TABLE 1.1 LEAST COUNT FOR MEASURING DEVICES

 

MEASURING DEVICE

NUMERICAL VALUE

UNIT OF MEASURE

Meter Stick

 

 

Balance

 

 

Stop Watch

 

 

Graduated Cylinder

 

 

 

Measure your bench work area from seam to seam and from the front edge of the bench top to the water trough. Record your values below using the least count concept. Determine the surface area of your work space.

 

SURFACE AREA = __________________ X __________________ = _____________________ cm2

Convert your answer for the surface area on page 1 to meters squared. Show your work.

 

 

 

 

 

SURFACE AREA = _______________________ m2

 

2. To make a measurement using significant figures, read all of the digits appropriate from your measuring device and then make an estimate of an additional decimal digit by determining the fractional portion your actual measurement exceeds the last digit you can read from the device. In essence, a significant figure is an extension of the least count that is made by guessing at an additional decimal place to the least count value. In an instance where a measurement is determined to be exactly on a least count line of a device, a zero is inserted to indicate that the number was exact and there was no significant figure.

 

Determine the length, width and height of a wooden block using the significant figures concept and enter your data in TABLE 1.2. Three measurements of each dimension are required and the averages obtained. Find the volume of your block by multiplying the averages you obtain for the length, width and height. Also remember, when two or more measurements are multiplied or divided, the number of significant figures in your final answer can not be greater than the number of significant figures in your measurement with the least number of significant figures. For example, if we multiplied the following measurements 1.2356 cm X 34.56 cm X 72.845689 cm; our answer would be 3110.68 not 3110.681088 since we have 34.56 cm (only two decimal places) as one of our numbers.

 

TABLE 1.2 VOLUME OF A WOODEN BLOCK

 

TRIAL

LENGTH (cm)

WIDTH (cm)

HEIGHT (cm)

1.

 

 

 

2.

 

 

 

3.

 

 

 

AVERAGE

 

 

 

 

VOLUME = length X width X height ________________ cm3

 

3. Determine the mass of your wooden block using a balance, FIGURE 1.1. Make sure that your balance is leveled and properly zeroed before beginning your measurements. Ask your instructor for assistance, if you need help.

 

MASS OF WOODEN BLOCK . __________________ g

 

4. The density of a substance is defined as the ratio of the mass to the volume of the substance. Determine the density of your wooden block using your data from procedures 2 and 3 above.

 

DENSITY = mass / volume . _________________ g/cm3

 

 

 

 

 

 

 

 

 

 

 

FIGURE 1.1

QUESTIONS:

1.                   Distinguish between least count and significant figures.

 

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2.                   Why do we try to avoid using the end of a meter stick?

 

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3.                   How can you increase the accuracy of your measurements?

 

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