Short notes-1 of chapter-1( physical quantities and Measurement) of class-7

 ☆ physical quantity-

• A quantity that can be measured is called a physical quantity. 

Or a measurable quantity is called a physical quantity.

• a physical quantity can be of two types:

     1. Scalar quantity- which can be expressed only by their magnitude.eg. mass, length, time ,distance, density ,volume, speed, temperature,  work, energy, power, pressure etc.

      2. Vector quantity- which requires the magnitude as well as the direction to express them.eg. force ,weight, velocity , displacement ,acceleration,magnetic field ,moment of force etc.

•  physical quantity= magnitude× unit

• basic quantities or fundamental quantities with their S.I. units:

1. Length - metre- m

2.Mass- kilogram- kg

3. Time- second-s

4. Temperature- Kelvin-K

5. Luminous intensity- candela-cd

6. Electric current- ampere-A

7. Amount of substance-mole-mol

☆ measurement-

- measurement is a comparison of an unknown quantity with a known fixed quantity of the same kind.

☆length -

• length is the distance between two points.

• SI unit is metre.

• Symbol is 'm'

• measured by measuring tape or metre ruler.

☆ mass-

• mass is the quantity of matter contained in the body.

• SI unit is kilogram.

• symbol is 'kg'

• measured by beam balance or an electronic balance.

☆ time-

• time is the interval of occurrence of an event.

Or 

the interval between two instances or events is called time.

• s i Unit is second.

• symbol is 's'

• measured by pendulum clock or watch.

☆ temperature-

• temperature is A quantity which measures the hotness or coldness of a body.

• SI unit is Kelvin.

• symbol is 'K'

• measured by a thermometer.

☆ measurement of volume-

• the space occupied by an object is called its volume.

• SI unit is Cubic metre or m³.

• 1 cubic metre is the volume of a cube with each side 1 metre long.

• other units of volume

Cubic centimetre, litre,dm³,mL,etc.

• relationship between different units-

 1m³=1m×1m×1m

        =100cm×100cm×100cm         (1m=100cm)

        =1000000 cm³

        =10⁶ cm³

1L=10-³ m³

1m³=1000L

1L=1000 cm³

1L=1000 mL.

1dm³=1dm×1dm×1dm

          =10cm×10cm×10cm    (1dm=10cm)

          =1000 cm³

         =1L

1L=1dm³

1mL=1cm³

☆ vessels for measuring the volume of liquids

• measuring cylinder-

• area of cross section of 10 centimetre square is is made up of either glass or plastic.

• it is is of capacity 100cm³ or 100mL.

• used in laboratory to measure the volume of liquids.

• used to find the volume of an irregular object by measuring the displacement of water or liquid by the object.

•Measuring beaker-

- used to measure a fixed volume of a liquid such as milk, oil  etc.

• available in different capacities such as 50ml, 100 ml ,200 ml, 500ml ,1000ml .

☆ measurement of volume of a liquid

• by using a measuring cylinder

• by using a measuring beaker

☆ measurement of volume of regular objects

• the volume of regular object is measured by finding its three dimensions that is Length ,breadth & height or  radius and then using the formula.

1 volume of a cube=side×side×side

                                  =s³

2. Volume of a cuboid= length× breadth× height                                            =l×b×h

                                         =A×h    (A=l×b)

 3. Volume of a sphere=4 π/3 × r³

4. Volume of a cylinder=π×r²×h

5. Volume of a cone=π/3 ×r²×h   ,

   π=22/7  or pie=3.14

☆ measurement of volume of an irregular body-

• volume of irregular shaped body is measured by using a measuring cylinder by the method of displacement of liquid.

• volume of a body of irregular shape= volume of liquid displaced by the body when it is immersed completely into the liquid.

• the difference in the final level from the initial level gives the volume of the liquid displacedi.e., V=V2 -V1   V2=final level ,V1=initial level.

☆ area-

•  The surface occupied by an object is called its area.

• SI unit of area is square metre.

• symbol is m²

• square metre is equal to the area of a square of side 1 metre.

1m²=1m×1m

• Bigger units of area are:

1 decameter² (are)=10m×10m

                                   =100m²

                                   =10²m²

1 hectare=100m×100m

                 =10000m²

                 =10⁴m²

1km²=1km×1km

         =1000m×1000m

         =10⁶m²

• smaller unit of area:

1cm²=1cm×1cm

         =1/100 m ×1/100 m

         =10‐²m×10-²m

         =10-⁴ m²

1mm²=1mm×1mm

           =10-³m×10-³m

           10-⁶m²

☆ measurement of area of regular objects:

• area of a regular object can be found by measuring the two dimensions that is length breadth or radius and then using appropriate formula.

1. Area of a square=side×side

2. Area of a rectangle= length× breadth

3. Area of a circle=π×r²

4. Surface area of a cylinder=2×π×r×length

5. Surface area of a sphere=4×π×r²

                     π=22/7

     Or    π=3.14     r=radius.

☆ measurement of area of an irregular object:

• by graphical method

• place the irregular object or lamina over a graph paper and draw its boundary line on the graph paper with a pencil .

•Area= the number of complete square + the number of squares half and more than half within the boundary line.

• area of one box is 1cm².