Measurement and Experimentation Introduction
The goal of physics is to provide an understanding of nature. The science of physics was developed to explain our physical environment. Great Physicists like Galileo, Newton, and Einstein etc. framed laws to explain the various phenomena in nature. These laws have been verified experimentally. Experiments in Physics involve the measurement of various quantities and a great deal of effort has gone into making these measurements as accurate and reproducible as possible. So certain basic standards of measurements have been established and units agreed upon internationally.
In no subject does measurement play as important a role as in science. Real science cannot exist without measurement. According to Lord Kelvin, one of the greatest scientists, unless you can measure what you are speaking about and express it in numbers you have not started 'Exact Science'.
Thus there are two aspects regarding measurements. One is actual MEASUREMENT of objects or happenings and the second is expressing that in terms of NUMBERS.
Physics is an exact science. It deals with accurate measurements. But the question comes up 'How much accuracy do we need to make our measurements accurate?'
The answer depends upon the purpose for which measurements are made. To know exact time we take to reach the school we may need to know the number of minutes we take to reach the school. But Olympic records need timings in fractions of seconds! For us the year is equal to 365 or 365.25 days. And it is acceptable. But ask an astronomer. He will say that it is equal to 365.242195 days! But apart from such astronomers, for whom is such accuracy important?
It is easy to measure the length of your page but if you are asked to find the height of a high rise building how would you do it? It is of course possible to do that by going to the terrace of the building, hanging a rope… etc. Not very convenient!
On the other hand one can estimate approximate height of a floor and then do some simple arithmetic to arrive at a figure which, though not accurate from the point of view of an architect, may serve our purpose. Thus even if accurate measurement is necessary it is always advisable to estimate. This would help; you to avoid silly mistakes that frequently take place while calculating.For better estimations, specially for large numbers, comparison is easier to make. For example in the above calculations it would be easier to compare the height of the high rise building in terms of a building with two or three storeys.
In measurements approximation also plays an important role. In day to day practice we always use approximation. You must have heard people saying "It is approximately five minutes walk from the station" or "Both of them are more or less of the same height" etc. Approximations also play an important role in science. To give you some idea about the size of an atom your chemistry teacher would say, "In a centimetre, there might be approximately 100 million atoms lying side by side!
For understanding the relationships between matter and energy, measuring them is very essential. There are thousands and thousands of different things around us. There are different kinds of forces around us and there are different kinds of energies that we come across every day. Thus there would be millions and millions of physical quantities and energies that could be measured. Yet you would be surprised to know that there are only six basic units from which all other units are derived. These basic units are the units of length, mass, time, electric current, temperature and luminous intensity. Out of these only three fundamental or basic units of measurements are used in mechanics.
These are the units length, mass and time. All the measurements in physics are related to these three fundamental units. All other units of measurements can be derived from these three fundamental units.
While discussing these units of measurement we must be clear about two terms - unit and measure number. For example, when we say that the length of a line is five centimeters, the unit we have chosen is centimeter and the measure number is five as the line is five times the unit length.
Most experiments in physics require the observations made to be quantitative rather than qualitative. If observations are only descriptive or qualitative, they are likely to be imprecise and could cause disagreements between experimenters. For example, scientists cannot merely say that an object is large or small. Instead they have to specify its size as a quantity, that is, with a number and using a standard unit such as kilogram. This is called a quantitative observation.
As science advanced through the centuries, the importance of accurate and uniform measurements was realized all over the world. In order to enable scientists working in different parts of the world to compare their measurements, a need for certain basic unit of measurement was felt and hence later a basic unit was defined.Unit is a standard for comparison. In earlier times the measurement of quantity of things was quite arbitrary. In many cases it was related to the dimension of different parts of the human body. These parts were chosen as "units" to measure these quantities. For example, for measuring length, distance between the nose and the fingers or outstretched hand was used as a unit. Can you imagine the confusion caused when different countries used different units or measures! This also caused a lot of inconvenience.
The prefixes used in the system are shown in table below:
The above system is called the Metric system, which literally means, "measuring system". In the Metric System there are two commonly used systems of measurement, one based on the Meter, Kilogram and Second (MKS) and the other on the Centimeter, Gram and Second (CGS).
Usually all small measurements are expressed by using the prefixes - deci, centi, milli, etc. with the units.
For large measurements, we use deca, hecto, kilo etc. as prefixes with the units. The symbol and meaning of each prefix is given below
Estimation by orders of Magnitude of Size,Mass, Time
Thus there are two aspects regarding measurements. One is actual MEASUREMENT of objects or happenings and the second is expressing that in terms of NUMBERS.
Physics is an exact science. It deals with accurate measurements. But the question comes up 'How much accuracy do we need to make our measurements accurate?'
The answer depends upon the purpose for which measurements are made. To know exact time we take to reach the school we may need to know the number of minutes we take to reach the school. But Olympic records need timings in fractions of seconds! For us the year is equal to 365 or 365.25 days. And it is acceptable. But ask an astronomer. He will say that it is equal to 365.242195 days! But apart from such astronomers, for whom is such accuracy important?
Estimation
On the other hand one can estimate approximate height of a floor and then do some simple arithmetic to arrive at a figure which, though not accurate from the point of view of an architect, may serve our purpose. Thus even if accurate measurement is necessary it is always advisable to estimate. This would help; you to avoid silly mistakes that frequently take place while calculating.For better estimations, specially for large numbers, comparison is easier to make. For example in the above calculations it would be easier to compare the height of the high rise building in terms of a building with two or three storeys.
Approximation
In measurements approximation also plays an important role. In day to day practice we always use approximation. You must have heard people saying "It is approximately five minutes walk from the station" or "Both of them are more or less of the same height" etc. Approximations also play an important role in science. To give you some idea about the size of an atom your chemistry teacher would say, "In a centimetre, there might be approximately 100 million atoms lying side by side!
Measurements
Everything that we use in our daily life is ultimately governed by principles of physics. All gadgets we use everyday at home, bicycles and cars, all different types of machinery and instruments, work on principles of physics. Hence to understand even the elementary working of these things, the study of physics is essential.For understanding the relationships between matter and energy, measuring them is very essential. There are thousands and thousands of different things around us. There are different kinds of forces around us and there are different kinds of energies that we come across every day. Thus there would be millions and millions of physical quantities and energies that could be measured. Yet you would be surprised to know that there are only six basic units from which all other units are derived. These basic units are the units of length, mass, time, electric current, temperature and luminous intensity. Out of these only three fundamental or basic units of measurements are used in mechanics.
These are the units length, mass and time. All the measurements in physics are related to these three fundamental units. All other units of measurements can be derived from these three fundamental units.
While discussing these units of measurement we must be clear about two terms - unit and measure number. For example, when we say that the length of a line is five centimeters, the unit we have chosen is centimeter and the measure number is five as the line is five times the unit length.
Quantitative Versus Qualitative
Back to TopAs science advanced through the centuries, the importance of accurate and uniform measurements was realized all over the world. In order to enable scientists working in different parts of the world to compare their measurements, a need for certain basic unit of measurement was felt and hence later a basic unit was defined.Unit is a standard for comparison. In earlier times the measurement of quantity of things was quite arbitrary. In many cases it was related to the dimension of different parts of the human body. These parts were chosen as "units" to measure these quantities. For example, for measuring length, distance between the nose and the fingers or outstretched hand was used as a unit. Can you imagine the confusion caused when different countries used different units or measures! This also caused a lot of inconvenience.
Metric Units in Common Use and their Relationship
At last in 1789 a system of measurement was invented based upon the powers of ten. Each unit quantity was divided into ten parts and each of these parts into further ten and so on. Multiples of the unit are ten, one hundred, one thousand etc. This was very logical. Once the size of the unit had been determined say, the "meter", submultiples were named decimeter, centimeter, millimeter for one tenth, one hundredth and one thousandth of a meter respectively. Multiples were named as the decameter (x 10), hectometer (x 100) and kilometer (x 1000) etc.The prefixes used in the system are shown in table below:
| Mega | Means | 106 |
| kilo | Means | 103 |
| Deci | Means | 10-1 |
| Centi | Means | 10-2 |
| Milli | Means | 10-3 |
| Micro | Means | 10-6 |
The above system is called the Metric system, which literally means, "measuring system". In the Metric System there are two commonly used systems of measurement, one based on the Meter, Kilogram and Second (MKS) and the other on the Centimeter, Gram and Second (CGS).
International System of Units
Basic Units in the SI System
Back to Top| Physical Quantity | Name of the Unit | Symbol |
|---|---|---|
| Length | meter | m |
| Mass | kilogram | kg |
| Time | second | s |
| Temperature | kelvin | K |
| Electric current | ampere | A |
| Luminous intensity | candela | cd |
| Amount of substance | mole | mol |
Usually all small measurements are expressed by using the prefixes - deci, centi, milli, etc. with the units.
For large measurements, we use deca, hecto, kilo etc. as prefixes with the units. The symbol and meaning of each prefix is given below
| Prefix | Symbol | Fraction/Multiple |
|---|---|---|
| Deci | d | 10-1 |
| Centi | c | 10-2 |
| Milli | m | 10-3 |
| Micro | μ | 10-6 |
| Nano | n | 10-9 |
| Pico | p | 10-12 |
| Femto | f | 10-15 |
| Atto | a | 10-18 |
| Deca | da | 101 |
| Hecto | h | 102 |
| Kilo | k | 103 |
| Mega | M | 106 |
| Giga | G | 109 |
| Tera | T | 1012 |
| Peta | P | 1015 |
| Exa | E | 1018 |
Derived Units
Back to Top| Quantity | Formula | Symbol (SI Unit) |
|---|---|---|
| Area | A=LxB | m2 |
| Volume | V=LxBXH | m3 |
| Density | D = Mass/Volume | kg m- 3 |
| Velocity | V = Distance/Time | m s-1 |
| Acceleration | a = Change in Velocity/Time | m-2 |
| Momentum | p = mass x velocity | Kg ms-1 |
| Force | F = Mass x Arceleration | N(newton) |
| Work | W = Force x Distance | J(joule) |
| Power | P = Work / Time | W (watt) |
| Potential Energy | P.E. = Force x Displacement = m xg xh | J(joule) |
| Kinetic Energy | KE. = (1/2) x mass x (Velocity)2 | J (joule) |
| Moment of Force | Moment = Force x Perpendicular Distance | Nm |
| Pressure | P = Force / Area | N m-2 or Pa(Pascal) |
Accuracy in Measuring
It is the smallest reading that can be accurately measured while using an instrument or a device. For example the least count of various measuring devices are listed below:
| Device | Least count |
|---|---|
| protractor | 1° |
| clock | 1 second |
| Ruler | 1 mm |
| Thermometer | 1° |
| Spring Balance | 1 gram |
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