Gravitation
"According to Newton's Universal Law of Gravitation : Every object in the universe attracts every other object with force that is directional proportional to the product of their mass and inversely proportional to the square of the distance between their centre."
g=G*m1*m2/d2 (G= Gravitational constant)
* It is attractive in nature.
* It is the weakest force but is a long range force.
Gravity (g)
"It is the force with which earth attract a body towards its centre."
Acceleration due to gravity (g) is the rate of increase in velocity of a body falling freely towards the earth.
* The value of "g" at the surface of the Earth is 9.8 m/s2
Variation of value of 'g'
Weight of body in a lift
"According to Newton's Universal Law of Gravitation : Every object in the universe attracts every other object with force that is directional proportional to the product of their mass and inversely proportional to the square of the distance between their centre."
* It is attractive in nature.
* It is the weakest force but is a long range force.
Gravity (g)
"It is the force with which earth attract a body towards its centre."
Acceleration due to gravity (g) is the rate of increase in velocity of a body falling freely towards the earth.
* The value of "g" at the surface of the Earth is 9.8 m/s2
Variation of value of 'g'
- When we go above the surface of the earth, gravity goes on decreasing.
- On going below the surface of the earth gravity goes on decreasing and become zero at the centre.
- Decreasing the rotational motion of the earth value of 'g' increase.
- When we go from equator towards the poles, value of g goes on increasing. g is maximum at poles and minimum at equator.
- If earth stop its rotation about its own axis then at the equator the value of 'g' increase and consequently the of body increase there.
- The value of g is maximum on the surface of the earth.
- Acceleration due to gravity at moon is 1/6th of the Earth, so weight of a person will be 1/6th of actual weight on the earth.
Weight of body in a lift
- If lift is stationery or moving with uniform speed( downward or upward), the apparent weight of body remains equal to the real weight.
- If lift is going up with uniform acceleration, the apparent weight become more than the real weight, and
- If the lift is going down with acceleration, apparent weight is less than real weight.
- If the lift is falling freely, the weight of the body in the lift get zero. This is called weightlessness.
- If the lift is going down and acceleration of lift is more than 'g' the body will get in contact with the ceiling (e.g. Free Fall of lift).
Satellite
The heavenly body(stars or celestial body) which revolves around the planet is called satellite.
- Moon is the natural satellite of the Earth, INSAT-B etc. is artificial satellite of Earth.
- The speed of satellite is independent on its mass.
- Every body inside a satellite feels weightlessness.
- The total energy of satellite is negative.
- Earth is rotate West to East. This rotation make the Sun and the stars appear to be moving across the sky East to West.
- Polar satellite revolves around the earth in polar orbit at a height of 800km app. Time period of these satellite is 84 min.
Artificial Satellite:-
1. Geostationary Satellite: Its time period is of 24 hrs it reflect TV signal and telecast TV programs. It revolves around height of 36000 Km.
2. Polar Satellite: Its time period is 84 minutes. It revolves around the earth's polar orbit. It is used for weather forecasting.
Escape Velocity:
The minimum threshold velocity that should be given to the body to make it escape from Earth's gravitational field.
- Given by:
where g is acceleration due to gravity (9.8 m/s2 ) and R is the radius of the Earth (6400 km).
- Escape velocity on the earth's surface is 11.2 km/s. Escape velocity at Moon's surface is 2.4 Km/s.
- Satellite are launched with the needed escape velocity.
Kepler's Law
- All planet move around the sun in elliptical orbit (nor round like eclipse) with sun at its one of foci (centre of eclipse).
- The areal speed of the planet around the sun is constant.
- The square of the speed of revolution of any planet around the sun is directly proportional to the cube of its distance from the sun.
Wave
A wave is a disturbance, which propogate energy from one place to other without transporting matter.
Wave broadly are of two types:
Longitudinal Wave
In this wave particles of the medium vibrate in the direction of propagation of wave.
Wave on springs or sound in air are example of longitudinal wave.
Transverse Wave
In this wave particle of the medium perpendicular to the direction of propagation of wave.
Wave on strings under tension, Wave on surface of water are example of this kind wave.
Electronic Wave
The wave which do not require any medium for their propagation i.e., which can propagate even through vacuum are called electromagnetic waves.
Light radio waves, X-rays are example of this kind wave.
Sound Wave
If there is a relative motion between source of sound and observer, the apparent frequency of sound heard by the observer is different from the actual frequency of sound emitted by the source. This phenomenon is called Doppler's Effect.
Echo: The repetition of sound due to reflection of sound waves is called an echo.
Intensity: It is defined as amount of energy passing normally per unit area held around that point per source unit time.
Pitch: The sensation of a frequency is commonly referred to as the pitch of a sound.
Sonar: It stand for sound navigation and ranging. It is used to measure the depth of a sea, to locate the enemy submarines and shipwrecks.
Sonic Boom: A sonic boom is the sound associated with the shock waves created by an object travelling through the air faster than the speed of sound.
Shock Wave: A body moving with supersonic speed in the air leaves behind it a conical region of disturbance which spreads continuously, this disturbance is called shock wave.
SONAR (Sound Navigation and Ranging). It is used to measure the depth of sea, locate an enemy submarine or shipwrecks. It produces ultrasound wave.
A wave is a disturbance, which propogate energy from one place to other without transporting matter.
Wave broadly are of two types:
- Mechanical Wave: (longitudinal wave and transverse wave)
- Electronic Wave.
Longitudinal Wave
In this wave particles of the medium vibrate in the direction of propagation of wave.
Wave on springs or sound in air are example of longitudinal wave.
Transverse Wave
In this wave particle of the medium perpendicular to the direction of propagation of wave.
Wave on strings under tension, Wave on surface of water are example of this kind wave.
Electronic Wave
The wave which do not require any medium for their propagation i.e., which can propagate even through vacuum are called electromagnetic waves.
Light radio waves, X-rays are example of this kind wave.
Sound Wave
- It is longitudinal mechanical wave.
- Frequency range of audible sound range is 20Hz to 20KHz( 20000Hz).
- The wave with frequency less than 20Hz are called infrasonic waves (produce by earthquake, volcanic eruption). Some birds can hear these sound.
- The wave with frequency more than 20KHz are called ultrasonic waves. These wave are used for sending signals measuring the depth of sea, in ultrasonography. Bats produce ultrasonic waves.
- Speed of sound is maximum in solid and minimum in gases.
- Speed of sound in air is 332 m/s, in water 1483 m/s, and in iron 5130 m/s.
- Speed of sound is depend on elasticity and density of the medium and also on temperature.
- Frequency of sound wave is fundamental quantity it does not change when sound enters from one medium to another but speed and wavelength changes.
- Speed of sound remains unchanged with the increase or decrease of pressure.
- The speed of sound increases with the increase of temperature of the medium.
- The speed of sound is more in humid air than in dry air because the density of humid air is less than the density of dry air.
If there is a relative motion between source of sound and observer, the apparent frequency of sound heard by the observer is different from the actual frequency of sound emitted by the source. This phenomenon is called Doppler's Effect.
Echo: The repetition of sound due to reflection of sound waves is called an echo.
Intensity: It is defined as amount of energy passing normally per unit area held around that point per source unit time.
Pitch: The sensation of a frequency is commonly referred to as the pitch of a sound.
Sonar: It stand for sound navigation and ranging. It is used to measure the depth of a sea, to locate the enemy submarines and shipwrecks.
Sonic Boom: A sonic boom is the sound associated with the shock waves created by an object travelling through the air faster than the speed of sound.
Shock Wave: A body moving with supersonic speed in the air leaves behind it a conical region of disturbance which spreads continuously, this disturbance is called shock wave.
SONAR (Sound Navigation and Ranging). It is used to measure the depth of sea, locate an enemy submarine or shipwrecks. It produces ultrasound wave.