Synopsis

• The observation of a phenomenon is made possible by using the five senses: sight, smell, touch, hearing and taste. 
• Our senses are not always reliable. They are subjective. 
• Sometimes it is necessary to make an exact measurement. 
• Physics is a science of measurement. 
• We use instruments to get an exact measurement. 
• Four basic measurements in our daily life are: measurement of length, measurement of mass, measurement of time, and measurement of temperature. 
• Measurement is basically a process of comparison of the given quantity with a standard unit. 
• For measuring a quantity we need a unit, and then we find the number of times that unit is contained in that quantity. 
• The unit selected for measurement should be of a convenient size and it must not change ‘with place or time. 
• The distance between two fixed points is called length. 
• The S.I. unit of length is metre (m). Its multiple is kilometre (km), where 1 km = 1000 m. Its sub multiples are centimetre (cm) and millimetre (mm), where 1 cm = 10^-2 m and 1 mm = 10^-3 m. 
• The FPS unit of length is foot (ft) and its sub multiple is inch where 1 ft = 12 inch and 1 ft = 30.48 cm. 
• The most common instruments used to measure length are the metre ruler and the measuring tape which are marked in cm and mm. 
• To measure a length accurately with a metre ruler, the scale should be placed with its markings close to the object and parallel to its r length. The eye is kept in front of and in line with the reading to be taken. 
• The quantity of matter contained in a body is called its mass. 
• The S.I. unit of mass is kilogram (kg). Its multiples are quintal and metric tonne. 1 quintal = 100 kg and 1 metric tonne =10 quintal = 1000 kg. Its sub multiples are gram (g) and milligram (mg) where 1 g = 10 kg and lmg = 10^-6 kg. 
• The FPS unit of mass is pound (lb) where 1 lb = 453.59 g. 
• Mass of a body is measured by using a beam balance or an electronic balance. 
• The interval between two instances or events is called time. 
• The S.l. unit of time is second (s), 1 s 1 / 86400 of a mean solar day. The C.G.S. and F.P.S. unit of time is also second (s). 
• The multiple unit of time are minute (mm), hour (h), day and year where 1 min = 60 s, 1 h = 3600 s, 1 day = 86400 s and 1 year = 3.15 × 10⁷ s. 
• The time at any instant is recorded by a pendulum clock or watch and the time interval of an event is measured by using a stop watch or a stop clock. 
• The temperature is the measure of degree of hotness or coldness of a body. 
• The S.I. unit of temperature is kelvin (K), but the common unit of temperature is degree Celsius (°C) and degree Fahrenheit (°F). 
• Doctors use a clinical thermometer to measure the patient’s body temperature. 
• The normal temperature of a human body is 37°C or 98.6°E 
• The total surface occupied by an object is called its area. Area is expressed as the product of measured length of two sides. 
• The S.I. unit of area is square metre (m²). 
• One square metre is the area of a square of each side one metre. 
• The bigger (or multiple) units of area are dam², hectare and square kilometre (km²), where 1 dam²=100 m²,1 hectare= 10⁴ m² and 1 km² = 10⁶ m² 
• The smaller (or sub multiple) units of area are cm² and mm² where 1cm² = 10^{– 4} m² and 1 mm² = 10^-6 m²