Measurement

Explain the concepts of measurement

Measurement is the process of assigning numbers to observations or events. It is the process in which the amount of values, data or quantity is obtained. Measurement is an important activity in Physics. During measurement, a scientist follows proper procedures and uses proper instruments so as to get exact amounts.

Importance of Measurement in Real Life

State the importance of measurement in real life

Measurement is among very important practices in several fields such as engineering, medicine, architecture, teaching, communication, transport and many more. It plays a great role in our daily life. Without measurement people would not be able to do things. Some of the importance of measurement can be seen in the following aspects:

 

1. Determination of time – Time helps us to plan our daily activities. Time can be measured in seconds, minutes, hours, days, years and so on. Time helps to know our age as well as historical events. It also helps us to control the occurrence of events e.g time for a chemical reaction to take place, laboratory practices, when to plant crops, when to harvest, and so on.

2. Determination of amount of quantities – It is important that we know the amount of food we want to buy or cook, the amount of water we want to use, amount of fruits we want to eat, size of shoes and clothing, the size of a house we want to live in and so on. Amount of quantities can be mass, volume or length.

3. Designing of equipment and materials – Materials and things like clothes, shoes, chairs, tables, television sets, computers, houses, cars, laboratory apparatus, airplanes, windows, mobile phones require the knowledge of measurement so as to make them meet the needs of the users.

4. Medical services – Doctors needs to know how much a patient is affected by a disease. Doctors will also want to give proper amount of medicine to cure the patient. All these activities require the doctor do some measurements.

5. Predicting weather conditions – Weather conditions help in planning for economic and transport activities as well as determination of the climate of a place. People need to know if it will rain, temperature of the day, humidity as well as wind speed and direction.

6. Understanding weight - Is that object too heavy to pick up by yourself or do you need to use something to lift it? Some may think this is not important but it is pretty easy to hurt yourself if you lift objects that are too heavy.

7. Transportation - How much weight is too much for a plane to take off or a car to move efficiently? How much fuel is needed to reach a certain point and how long will it take to get somewhere? Yes, measurements play a significant part in transportation.

 

Therefore, life could very hard and unpredictable without the knowledge and use of measurement in our daily life.

A Fundamental Quantity

Define a fundamental quantity

A quantity is the amount, size or extent of a material, object or event expressed in numbers. Examples of quantities are mass, speed, distance, force, and energy. A quantity has two parts, a number and a unit e.g. A mass of 12 kg has ‘12’ as a number and ‘kg’ as a unit.

 

A Unit is the standard which is used to explain measurement of a body like; kilogram, metre, seconds etc.

A quantity may be fundamental or derived. A fundamental quantity is the quantity which cannot be explained in form of other quantities. There are seven fundamental physical quantities namely mass, length, time, temperature, electric current, amount of substance and luminous intensity. Fundamental quantities cannot be derived into other quantities.

Three Basic Fundamental Quantities of Measurement

Mention three basic fundamental quantities of measurement

Among the seven fundamental physical quantities, there are three basic fundamental quantities which are mass, length and time.

Mass is defined as the amount of matter contained in a body. Length is the distance between two points or objects, while time can be defined as the gap or space between events.

 

SI unit (International System of Units): Is the system of units which is used internationally to measure seven basic physical quantities.

Note: With the exception of temperature, amount of substance and luminous intensity, other units of measurement that are smaller or larger than the most commonly used units are expressed by attaching a prefix to the most commonly used units.

 

Greater than 1 unit

Giga(G) = 1,000,000,000 (10ˆ9)

Mega(M) = 1,000,000 (10ˆ6)

Kilo(K) = 1,000(10ˆ3)

Hector (h) = 100(10ˆ2)

Decca(da) = 10(10ˆ1)1

Less than 1 unit

Deci (d) = 1/10 (10ˆ-1)

Cent (c) = 1/100(10ˆ-2)

Mill (m) = 1/1000 (10ˆ-3)

Micro(μ) = 1/1,000,000(10ˆ-6)

 

Measurement of length

Length is the distance between two points, objects or spaces. The SI unit of length is the meter (m). Other commonly used units are kilometre (km) and centimetre (cm). In the laboratory, length is measured by using instruments such as meter rule, vernier caliper and micrometer screw gauge.

Meter rule

It measures length to the accuracy of 0.001 m or 0.1 cm. It is calibrated from 1 cm to 100 cm which is equal to 1m length. It is used to measure linear length (lengths with no curves).

 

How it works

Align a meter rule close to and along the edge of the length of the object to be measured.

Take the reading by looking at the mark from vertically upwards to avoid parallax errors.

Record the reading.

Vernier caliper

It measures length to the accuracy of 0.01cm (0.1mm). It is used to measure lengths in the range of 1.0cm to about 12.0cm. It has two scales, namely the main scale and the vernier scale. The main scale is marked in cm from 1 cm to 12 cm, while the vernier scale is marked with 10 marks measured in mm. It has two outside jaws used to measure the length and external diameter of cylinders and pipes. It has two internal jaws for measuring the internal diameter of cylinders and pipes.

 

The inside jaws are used to measure the inside diameter, while the outside jaws are used to measure the outside diameter. The vernier slides over the main scale.

How to read:

Fit the object to be measured between the jaws, and make sure not to press the object.

Record the reading on the main scale by reading the mark which is just behind the zero mark of the vernier scale.

Record the reading on the vernier scale by reading the mark which coincides with the mark on the main scale.

The length of the object is obtained by adding the reading from the main scale and the reading on the vernier scale.

Micrometer screw gauge

It measures small lengths to the accuracy of 0.001cm (0.01mm). It is used to measure the diameter of wires and ball bearings. It can measure small lengths up to about 2.5cm. It has a spindle with a linear scale on one of its side. It has a vernier scale (circular scale) on its thimble. The vernier scale has 50 equal marks each measuring 0.5mm.

 

How to read a micrometer screw gauge:

After fitting the object between the anvil and spindle, take the reading on the linear scale by recording the last mark visible. The reading is in mm.

Record the reading if there is a mark below the datum line or reference line.

Take the reading on the vernier scale by recording the mark which coincides with the datum line of the sleeve in mm.

The length/diameter of the object in mm is obtained by adding the two readings.

Precautions when using a micrometer screw gauge:

1. Before use, the faces of anvil and spindle should be wiped clean to remove any dirty particle which would give false readings.

2. Check and record for zero error then + or –the correction to the final answer.

Time

It is the gap between two occasions or events. The SI unit of time is second (s). Other units used are minutes (min), hours (h), days, etc.

 

1min = 60s

1h = 3600s

1day = 86400s

The instruments for measuring time are clocks and watches.

In the laboratory, time is measured by using the stopwatch. Stop watches are used for timing laboratory experiments. Stop watches may be mechanical or digital. Digital stop watches are more accurate than mechanical stop watches.

 

Basic Apparatus/Equipment Used for Measurement

Describe basic apparatus/equipments used for measurement

Several experiments are carried out in the physics laboratory by a physicist. The experiments involve measurements which are to be done by using proper instruments. Some of the common measurements in the laboratory are the measurements of volume, weight and density.

 

Volume

Volume is the amount of space occupied by a substance. The SI unit is cubic meter (mˆ3).Other units used are cubic centimetre (cmˆ3) and litre(l).

Instruments used to measure the volume of liquids:

Measuring cylinder-used for measuring or pouring out various liquids.

Measuring flask and pipette are used for getting fixed pre-determined volume.

Burette-used to deliver any required volume up to its total capacity.

How to read volume measuring instruments (precautions).

Readings are always taken at the level of the bottom of the meniscus or curved surface of the liquid. Mercury is an exception as its meniscus curves downwards.

Care should be taken to place the eye correctly to avoid parallax errors. When taking readings, the pipette and burette must be upright and the cylinder and flask must stand on a horizontal bench otherwise errors may arise from tilting.

Measuring volume of irregular objects.

The volume of an irregular solid can be determined by measuring the volume of water displaced in a measuring cylinder directly or with the aid of an overflow eureka can.