Nature Of The Physical World And Measurement : Nature Of The Physical World And Measurement
Forces of Nature : Forces of Nature Sir Issac Newton,
“Force is the external agency applied on a body to change its state of rest and motion”
Gravitational force
Electromagnetic force
Strong nuclear force
Weak nuclear force
t : t
Expressing Larger And Smaller Physical Quantities : Expressing Larger And Smaller Physical Quantities
Slide 5: Light Year
It is the distance travelled by light in one year in vaccum.
1 Light Year = 9.467 x 1015m
Astronomical unit
It is the mean distance of the centre of the sun from the centre of the Earth.
1 Astronomical Unit (AU) = 1.496 X 1011m LIGHT YEAR AND ASTRONOMICAL UNIT
Slide 6: Determination of Distance
Laser pulse method
Determination of mass
Determination of time
Atomic clocks – 1013 sec
Quartz clocks – 109 sec
Significant figures : Significant figures The number of meaning digits in a number is called the number of significant figures.
RULES
All the non- zero digits in a number are significant.
All the zeros between two non-zeros digits are significant, irrespective of the decimal point.
The zeros at the end without a decimal point are not significant.
The trailing zeros in a number with a decimal point are significant
Significant Figures Examples : Significant Figures Examples 0.0631 – Three Significant Figures.
56700 - Three Significant Figures.
0.00123 – Three Significant Figures.
30.00 – Four Significant Figures.
6.320 – Four Significant Figures.
600900 – Four Significant Figures.
346.56 – Five Significant Figures
5212.0 – Five Significant Figures.
Rounding Off : Rounding Off If the insignificant digit is more than 5,
The preceding digit is raised by 1.
If the insignificant digit is not more than 5,
There is no change.
If the insignificant digit is 5
Even
there is no change.
Odd
The preceding digit is raised by 1.
Rounding Off Examples : Rounding Off Examples 53.473 kg – 53.6 kg
0.575 m – 0.58 m
0.495 – 0.50
Errors in Measurement : Errors in Measurement Constant Errors
It is due to faulty calibration of the scale in the measuring instrument.
Systematic Errors
These are errors which occur due to a certain pattern or system.
Gross Errors
Improper setting of the instrument.
Wrong recording of the observation.
Not taking into account sources of error and precautions.
Usage of wrong values I the calculation.
Random Errors
It is very common that repeated measurement of a quantitative values which are slightly different from each other.
Dimensional Analysis : Dimensional Analysis Dimensions of a physical quantity are the powers to which the fundamental quantities must be raised.
Slide 13: Dimensional Quantities
Dimensional variables are those physical quantities which possess dimensions but do not have a fixed value.
Ex. Velocity, force, etc.,
Dimensionless Quantities
There are certain quantities which do not possess dimension .
Ex. Strain, angle, specific gravity, etc.,
Principle of homogeneity of dimensions
An equation is dimensionally correct if the dimensions of the various terms on either side of the equation are the same.
Ex. A+ B = C is valid only if the dimensions of A, B & C are the same.
Uses of Dimensional Analysis : Uses of Dimensional Analysis Convert a physical quantity from one system of units to another.
Check the dimensional correctness of a given equation.
Establish a relationship between different physical quantities in an equation.
Limitations of Dimensional Analysis : Limitations of Dimensional Analysis The value of dimensionless constants cannot be determined by this method.
This method cannot be applied to equations involving exponential and trigonometric functions.
It cannot be applied to an equation involving more than three physical quantities.
It can check only whether a physical relation is dimensionally correct or not. It cannot tell whether the relation is absolutely correct or not.