chapter 1 Physical quantities and Measurement class 7th physics скачать в хорошем качестве

chapter 1 Physical quantities and Measurement class 7th physics

What are physical quantities? Measurement of Area Area of Regular/Irregular Shapes Measurement of volume Volume of Regular/Irregular Shapes Density Speed What are physical quantities? Quantities that can be measured are known as physical quantities. For example length distance mass time temperature area volume, etc. The amount of surface acquired by an object or a plane figure is called its area The SI unit of area is square metre or m² Mutiples are used for larger measurements. Multiples of area are hectare, square kilometres(km²) 1 hectare= 100m×100m = 10000 m² 1 km²= 1km × 1km = 1000m× 1000m = 1000000m² Submutiples are used for smaller measurements. Multiples of area are cm², mm² 1 cm² = 1cm×1cm = 1/100m × 1/100m = 1/ 10000 m² 1 mm²= 1mm × 1mm = 1/10cm × 1/10cm = 1/100 cm² Plane figures like rectangle, square, circle, triangle have regular shapes the area of such figures can be determined by using certain formula. Area of regular shapes can also be measured by the use of a graph paper. Area of Irregular shape using graph paper If area of the irregular surface is small we prefer to use mm² (square millimetre) grid instead of a centimetre( cm) grid but the method is exactly the same. If one has a spherical ball of radius R then its total surface area is given by A= 4πr² The space occupied by an object is called its volume. The SI unit of volume is m³ or cubic meter Submultiple units of volume One a cubic metre is the unit of volume which is used to measure the volume of big bodies like volume of a tank filled with water or volume of a room. A more convenient unit of volume is Cubic centimetre or cm³. 1 m³= 1m×1m×1m 1m³= 100cm×100cm×100cm 1m³= 1000000cm³ A still smaller unit of volume is Cubic millimetre(mm³) 1cm³= 1cm×1cm×1cm 1cm³= 10mm×10mm×10mm 1cm³= 1000 mm³ The volumes of liquids like milk, Oil, petrol, etc are measured in litres and millilitres. The inner volume of a container, which holds a liquid, is known as its capacity. Thus, capacity is the space inside the container. The SI unit of capacity is litre. It’s submultiples and multiples are as follows: 1 centilitre( 1 cL ) = 1/100 litre(L) 1 millilitre ( 1mL ) = 1/10 centilitre ( cL ) = 1/1000 litre(L) 1 kilolitre ( 1 kL ) = 1000 litres (L) A cube, a cuboid, a sphere and a cylinder are regular solids as they have definite geometric shapes. Volume of these regular solids can be determined by using certain formulae. Volume of cube = a3 Volume of cuboid = l x b x h Volume of sphere = Volume of cylinder = pie r2 h Each side of an aluminium cube is a 4 cm. Find its volume as well as total surface area. A tank of length 32 m and breadth 20 m is filled with water. The depth of water in the tank is 2.4 m. Calculate the volume of water contained in the tank. Vessels used for measuring volumes/ capacities- Measuring cylinder and Measuring beaker Measuring cylinder is used in a laboratory to measure the volume of liquids and a regular solids of small size. Measuring can is used to measure the volume of kerosene and lubricating oils. Measuring beakers are commonly used to measure volume of milk and edible oil . Graduated cylinder is generally used by pharmacists to measure the volume of liquid medicines. 1cm³= 1 mL 1000 cm³ = 1L 1 m³ = 1000 L or 1 kL Volume of a given liquid can be easily measured by using ; Graduated cylinder Measuring(Graduated)beaker. By using measuring (graduated) cylinder: Take a clean and dry measuring cylinder. Now, pour the liquid, whose volume is to be noted, into the measuring cylinder. You will find that the liquid surface is slightly curved. This curved shape is called the meniscus. Now, note the reading at the lower level of the meniscus. This gives the volume of the liquid. Regular solids have no definite geometrical shape so we cannot determine the volume directly using a formula. we can determine the volume of irregular solid with the help of measuring cylinder: Numerical: Water is filled in a measuring cylinder and reading of water meniscus is 48 ml. When a small copper cylinder is immersed into the water, the meniscus reading become 65.5 ml. What is the volume of copper cylinder? The mass of an object contained per unit volume is called density. A piece of iron weighs 312 gram and has a volume of 40 cm³. Find the density of iron. Relation between SI and CGS Units of Density 100 ml of kerosene weighs 82 g. Calculate the density of kerosene in kg/m³. A lead sphere of radius 2 cm weighs 352 g. Determine the density of the Lead sphere. 2. A wooden cube of side 10 cm weighs 800 gram. determine the density of wood in kg/m³. When measuring cylinder is partially filled with water, the volume reading is 48 mL. when a glass stopper is immersed into water the volume reading is 74 mL. what is the volume of the glass stopper? If the mass of the glass stopper is 65 g, Density of irregular solid lighter than water Displacement method Density of a regular solids heavier than water and insoluble in it