### Coulomb Law

The magnitude of the electrostatic force of interaction between two charge points is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them.

### Wave

“A wave is a disturbance, which propagates energy from one place to the other without the transportation of matter.” A wave transmits information or energy from one point to another in the form of signals, but no material object makes this journey. The frequency of a wave is obtained by including a factor of time in the mix. We are completely dependent on waves for all of our wireless communications.

### Types of Waves in Physics

Wave is a propagation of disturbances that passes through a medium in an organized way. There are two types of waves which are longitudinal and transverse. While transverse waves are in which the medium vibrate perpendicular to the direction of propagation of the wave. On the other hand, in longitudinal wave the particles move in the same direction to the wave. Check out the types of waves and their properties below.

- Mechanical wave (longitudinal wave and transverse wave)
- Electromagnetic wave
- Matter Wave

**Heat and Thermodynamics**

**Heat**

- Heat is a form of energy, which measures the sensation or perception of warmness or coldness of a body or environment
- Its unit is a calorie, kilocalorie or joule.
**1 calorie = 4.18 joule**.

### Temperature

- Temperature is the measurement of the hotness or coldness of a body.
- When two bodies are placed in contact, heat always flows from a body at a higher temperature to a body at a lower temperature.
- An instrument used to measure the temperature of a body is called a thermometer.
- The normal temperature of a human body is
**37**^{0}C or 98.4^{0 F} - – 40
^{0}is the temperature at which Celsius and Fahrenheit thermometers read the same. - The clinical thermometer reads from
**96**^{0}F to 110^{0} - The white roof keeps the house cooler in summer than the black roof because a white roof reflects more and absorbs fewer heat rays whereas the black roof absorbs more and reflects fewer heat rays.
- Ice wrapped in a blanket does not melt away quickly because the woollen blanket is a bad conductor of heat.
**Silver is the best conductor of heat.****Cooking utensils**are made of aluminium, brass, and steel because these substances**have low specific heat and high conductivity.**

**Motion**

**Scalar Quantities:** Physical quantities which have magnitude only and no direction are called scalar quantities.**Example:** Mass, speed, volume, work, time, power, energy etc.

**Vector Quantities:** Physical quantities which have magnitude and direction both and that obey triangle law are called vector quantities.**Example:** Displacement, velocity, acceleration, force, momentum, torque etc.

Electric current, though has a direction, is a scalar quantity because it does not obey triangle law.

Moment of inertia, pressure, refractive index, stress are **tensor **quantities.

**Distance:** Distance is the actual path travelled by a body in a given period of time.

**Displacement: **Displacement is the shortest distance.

- The change in the position of the object in a given period of time
- Distance is a scalar quantity whereas displacement is a vector quantity both having the same unit (metre)
- Displacement may be
**positive, negative or zero**whereas distance is always**positive.**

**Speed: **Distance travelled by the moving object in the unit time interval is called speed i.e. speed = Distance/ Time

- It is a scalar quantity and its SI unit is meter/second (m/s).
- The speed of an object at any instant is called instantaneous speed.
- An object is said to be travelling with non-uniform speed if it covers an unequal distance in an equal interval of time.

**Velocity: **The velocity of a moving object is defined as the displacement of the object in unit time interval.

- It is a vector quantity and its SI unit is meter/second.
- If a body goes to equal displacement in an equal interval of time then it is called uniform velocity.
- If a body undergoes unequal displacement in equal interval of time then it is called variable velocity.
**Relative velocity**= V_{1}+V_{2}if two travels in the**opposite**direction

=V_{1}-V_{2}if two travels in the**same**direction

**Acceleration: **Acceleration of an object is defined as the rate of change of velocity of the object.

- It is a
**vector**quantity and its SI unit is meter/second^{2}(m/s^{2}) - If velocity decreases with time then acceleration is negative and is called
**retardation.** - If acceleration does not change with time it is called
**constant**acceleration. - Some equation of acceleration;

** V=u+at**

** S=ut+at ^{2}/2**

** V ^{2}= u^{2}+2as**

Here v=final velocity, u is initial velocity, t is a time interval, a is acceleration and s is the distance travel.

**Circular Motion: **The motion of an object along a circular path it is called circular motion. If the object moves with uniform speed, its motion is uniform circular motion.

- Uniform circular motion is an accelerated motion because the direction of the velocity changes continuously.

**Angular Displacement and Velocity:**

- The angle subtended at the centre of a circle by a body moving along the circumference of the circle is called angular displacement of the body.
- Its unit is radian.
- Angular displacement= length of arc/radius of the circle
- The time rate of change of angular displacement is called angular velocity.

It is generally denoted by ω and

**Force:**

- Force is that external cause which when acts on a body change or tries to change the initial state of the body.
- Its SI unit is
**Newton(N).** - A body is said to be in equilibrium if the sum of all the forces acts on the body is
**Zero.** - The nuclear force is the strongest force.

**Momentum:**

- Momentum is the property of a moving body and is defined as the product of mass and velocity of the body i.e.
- Momentum = mass x velocity.
- It is a vector quantity. Its SI unit is kg-m/s.

**SSC Physics Newton’s Law**

**Newton first law**

If no external force acts on a body then it remains in the same state of rest or motion that is in its present state.

**The inertia of Rest:**

**Inertia**is the property of a body by virtue of which it opposes any change in its state of rest or of uniform motion.- When a bus or train at rest starts to move suddenly the passengers sitting in it feels a jerk in backward direction due to the inertia of rest.
**Dust particle**comes out of a carpet if we beat it with the stick.- A passenger jumping out of a train is advised to jump in the direction of the bus and ran for a short distance.

**The inertia of Motion: **When a running bus or train stops suddenly, the passengers sitting in it jerk in the forward direction due to the inertia of motion.

**Newton’s second law of motion: **The rate of change in momentum of a body is directly proportional to the applied force on the body and takes place in the direction of the force.

If F = force applied, a = acceleration produced and m = mass of body

then F = ma.

**Newton’s Third Law of Motion:** To every action, there is an equal and opposite reaction.

Examples of third law –

- Recoil of a gun
- Motion of rocket
- While drawing water from the well, if the string breaks up the man drawing water falls back.

### Gravitational Force and Satellites

**Gravitation:**

Each and every massive body attracts each other by virtue of their masses. This phenomenon is called gravitation.

**Newton’s law of Gravitation**

The gravitational force of attraction between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

**Gravitational force (F)=Gm1m2****/ r ^{2}**

- Where G is the gravitational constant its value is
**6.67×10**^{-11}Nm^{2}kg^{-2.} - m1, m2 is the mass of two bodies and r is the distance between them.
- Gravitational force is central as well as conservative force.

**Acceleration Due to the Gravity of Earth**

- The acceleration produced in a body due to the gravitational pull of the earth is called acceleration due to gravity.

g=GM/R^{2 }where M is the mass of the earth and R is the radius of the earth. - The value of g changes slightly changes from place to place but its value near the earth’s surface is
**9.8ms**^{-2.} - Gravitational force is the
**weakest**force in nature.