8TH STANDARD NOTES AND QUESTIONS ON MEASUREMENT OF LENGTH, MASS AND TIME, DENSITY , MASS AND WEIGHT

Length : It is measured in meters using a ruler

conversions    :   1m = 100cm, 1cm=10mm , 1000m = 1Km

Mass : It is measured in Kg using a pan balance/spring balance.

Conversions   : 1kg = 1000g

Time : It is measure in seconds using stopwatch / watch

conversion :   1hour = 60 Minutes , 1minute = 60 seconds

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ACCURATE MEASUREMENT

The length can be measured accurately by taking more readings .

The thickness of the paper can be measured by taking a bunch of sheets and measuring it with the screw gauge.
calculating the thickness of 1 sheet by dividing the readings by no. of sheets

For example the thickness of 10 sheets are 0.012cm
then the thickness of 1 sheet is 0.0012cm

Time period of the pendulum is measured accurately by taking more number of swings.

take 10 or 20 0scillations and then calculate it for one oscillations.

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MASS AND WEIGHT

Mass : Its the matter present in the object.

Weight : Its the gravitational force exterted on the object

To calculate weight
you can use the formula

W=Mg

M- mass  ,    g- acceleration due to gravity

Value of g = 10N/Kg

Mass remain constant througout the universe.

weight keep on changing according to the gravitational force exerted by the different planets
(Hope you remember that jupiter has more gravitational force, so on jupiter your weight will increase.)

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DENSITY

The density of a material is defined as its mass per unit volume. The symbol of density is ρ (the Greek letter rho).

Mathematically: Density = Mass Divided By Volume

where:

ρ (rho) is the density,

m is the mass,

V is the volume.

The SI unit for density is:

§                     kilograms per cubic metre (kg/m³)

* NOTE: Significance of the density is to find the purity of the substance