Physics notes

What is Physics?

Physics is a branch of science which studies physical and natural phenomena around us.

Examples of natural phenomena are formation of rainbow, solar eclipse, the fall of things from up to down, the cause of sunset and sunrise, formation of shadow and many more.

Physics mostly answers whys rather than what and it gives scientific, systematic and consistent explanation based on the concepts of physics.

Physics knowledge will increase as the flow of time; new concepts will replace old concepts if proven to be accurate.

The word physics evolved from ‘physikos’ a Greek word for nature.

There are two main divisions of physics which are:
a. Classical physics: motion and energy, mechanics, force and motion, heat, sound, electricity, magnetism and light.
b. Modern physics: atomic, molecular and electron physics, nuclear physics, relativity, origin of universe, astrophysics.

Base and derived Quantities

Physical quantities are quantities that can be measured. e.g. Length, Temperature, Speed, Time.

Quantities or qualities that cannot be measured are not physical quantities. e.g. happiness, sadness etc.

Physical quantities can be divided into Base quantities and Derived quantities.

(i) Physical quantities are quantities that can be measured or can be calculated.
(ii) The base quantities are “building block” quantities from which other quantities are derived from.
(iii) The base quantities and their S.I. units are:

* Base quantities S.I. units
* Mass - kg
* Length - m
* Time - s
* Electric current - A
* temperature - K

(iii) Derived quantities are quantities derived (iv) Examples of derived quantities.

* Derived quantities S.I. units
* area - m2
* density - kg m-3
* weight - N
* velocity - m s-1
Standard Notation: To express very large or very small numbers.
Example; A X 10 n (ten to the power of n), n must be an integer and 1 ≤ A < 10

Scalar and vector quantities

Scalar quantities: Quantities that have magnitude only. ( Speed, mass, distance)

Vector quantities: Quantities that have magnitude and direction. (Velocity, Weight, Displacement)

Measurement

A micro balance is used to measure minute masses. It is sensitive but not very accurate.

Vernier callipers are usually used to measure the internal or external diameter of an object.

A micrometer screw gauge is used to measure the diameter of a wire of the thickness of a thin object.

All measurement must consider this:

Accuracy: Ability of the instrument to measure the true value or close to the true value. The smaller the percentage error, the more accurate the instrument is.

Sensitivity of an instrument is the ability of the instrument to detect any small change in a measurement.

Consistency: ability of the instrument to produce consistent measurement.(the values are near to each other). The lower the relative deviation, the more consistent the measurement is.

How to increase accuracy?
- repeat the measurements and get the mean value.
- correcting for zero error.
- avoiding parallax error.
- use magnifying glass to aid in reading.

The sensitivity of a mercury thermometer can be increased by;
-having a bulb of thinner wall.
-having a capillary tube of smaller diameter or bore.

Scientific Investigation

A variable is a quantity that can vary in value.

Manipulated variable is a variable that is set or fixed before and experiment is carried out. it is usually plotted on x- axis.

Responding variable is a variable that changes according to and dependent to manipulated variable. it is usually plotted on y-axis.

Fixed variable is fixed and unchanged throughout the experiment.

Inference: state the relationship between two VISIBLE QUANTITIES in a diagram or picture.

Hypothesis: state the relation ship between two MEASURABLE VARIABLES that can be investigated in a lab.

How to tabulate data?

-the name or the symbols of the variables must be labeled with respective units.
-all measurements must be consistent with the sensitivity of the instruments used.
-all the calculated values must be correct.
-all the values must be consistent to the same number of decimal places.

A graph is considered well-plotted if it contains the following:
- a title to show the two variables and investigation.
- two axes labeled with correct variables and units
- scales must be chosen carefully and graph must occupy more than 50% of the graph paper.
-all the points are correctly drawn.
-the best line is drawn.