PHYSICS ALL INFORMATION
Physics is that branch of natural science in which matter and energy and their interactions are studied. Physics is the basic science of the natural world, because the development of other branches of science depends to a great extent on the knowledge of physics.
1.Unit
Unit: The reference standard for measurement of any quantity is called unit There are two types of units – fundamental unit and derived unit. S.1. The number of units given in the system is seven, which is shown in the table below.
physical amount 2. mass 1. basic units of meter =m, kilogram = kg, 3. time second, kelvin =k 5. Electric current ampere =A, 6. Light intensity candela cd (cand) 7. Quantity of substance mole mol (mode)1. plane angle 5.1. of the complementary basic unit radian rad (rad)2. Solid steradian angle 5.1. New names and symbols for some old units Degree Centigrade, °C (old) Degree Celsius, °C 1. Fever 2.Frequency (New) Vibrations per second, cps Hertz, Hz (new) (Old)3. Luminous in-tensity Candle power, C.P. (old) candela, cd (new) All those units which are expressed with the help of basic units are called derived units. Light year is used to measure very large distances, that is, light year is the unit of distance. 1 light year – 9.46 x 10 meters The largest unit of measuring distance is parsec. 1 parsec – 3.26 light years – 3.08 × 10 m Sister’s C.G.S. The unit in the system is dyne and S.I. The unit in the system is Newton. The CGS unit of work is the unit. In the system the unit is erg and in the 5.1 system 1 newton – 10 dynes 1 jud – 10 args
SPEED
Scalar Quantity: A physical quantity which has only magnitude and no direction is called a scalar quantity: such as mass, speed, volume, work, time, energy etc. Note: Electric current, temperature, pressure are all scalar quantities.
Vector Quantity: Such physical quantities, which have magnitude as well as direction and which are added according to certain rules of addition, are called vector quantities. Like velocity, displacement, force, acceleration etc.
Distance: The length of the path traveled by an object in a given period of time is called distance. This is a surplus amount. It is always positive (+ve).
Displacement: The perpendicular (minimum) distance between two particles in a certain direction is called displacement. This is a vector quantity. Its S.1. The unit is meter. Displacement can be positive, negative or zero.
Speed: The distance traveled by an object per second is called speed. That is, speed =. Its S.I. Unit m/s. Is. distance time it is a scalar quantity
Velocity: The rate of displacement of an object or the distance covered by the object per second in a certain direction is called. It is a vector quantity. Its S.I. Unit m. From. Is.
Acceleration: The rate of change in velocity of an object is called ‘acceleration’. It is a vector quantity. Its 51 units are m/s. Is. If the velocity of the object decreases with time, the acceleration is negative, which is called retardation.
Projectile Motion: When a body moves under such a constant acceleration whose direction is different from the velocity direction of the body, then both the magnitude and direction of the velocity of the body keep changing with time. Due to this, the body moves on a curved path in the plane. This motion is called projectile and the curved path is called trajectory, it is always parabolic. An arrow released from a bow, a bomb dropped from a ship, a ball fired from a cannon etc. has a parabolic shape. These are all examples of projectile motion
Gravity
Newton’s Law of Gravitation: The force of attraction acting between any two bodies is directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between them.
Gravity: According to Newton’s gravity, an attractive force acts between two bodies. If one of these bodies is Earth, then this force of attraction is called gravity. That is, gravity is the force of attraction with which the Earth pulls any object towards its center. The acceleration produced due to this force is called acceleration due to gravity (g), whose value is 9.8 m/s². The acceleration due to gravity (g) does not depend on the shape, size, mass etc. of the object.
change in value of g
1. The value of 4 decreases as we go up or down from the earth’s surface.
2. The value of ‘g’ is maximum at the poles of the Earth.
3. The value of ‘g’ is minimum at the equator.
4. The value of ‘g’ decreases as the rotation speed of the Earth increases.
5. The value of ‘g’ increases as the rotation speed of the Earth decreases.
Note: If the Earth starts rotating at a speed 17 times more than its current angular speed, then the weight of an object placed on the equator will become zero. That means there will be a state of weightlessness. But there will be no change in the value at the pole. In such a situation the duration of the day will reduce from 24 hours to 1.4 hours (84 minutes). If the Earth stops rotating around its axis, the value of g will increase at all places except the poles.
Weight of a body in lift:
1. When the lift goes upward, the weight of the body in the lift appears to increase.
2. When the lift goes downwards, the weight of the body in the lift appears to decrease.
3. When the lift moves up or down with uniform velocity, there appears to be no change in the weight of the body in the lift.
4. If the rope of the lift breaks while descending then it falls down like a free body. In such a situation, the weight of the body in the lift is zero. This is the state of weightlessness.
5. If the acceleration of the lift while descending is more than the acceleration due to gravity, then the body in the lift will rise from its floor and hit its ceiling.
Kepler’s law related to planetary motion
1. Every planet revolves around the Sun in an elliptical orbit and the Sun is located at a focal point of the planet’s orbit.
2. The areal velocity of every planet remains constant. Its effect is that when the planet is near the Sun, its velocity increases and when it is far away, its velocity decreases.
3.The time taken by the planet to complete one revolution around the Sun is called its revolution period (T), the square of the revolution period (T2) is proportional to the cube (1) of the average distance (r) of the planet from the Sun. , i.e. T²³
That is, planets that are further away from the Sun also have a longer rotation period. Example: Mercury, the nearest planet to the Sun, has a rotation period of 88 days, while Neptune, the farthest planet, has a rotation period of 165 years.
Note: I.A.U. has removed Pluto from the category of planet, hence now the distant planet is Neptune.
Satellite: The body revolving around a planet is called satellite of that planet. For example, the Moon is a satellite of the Earth.
Orbital Speed of a Satellite:
1. The orbital speed of a satellite depends on its height from the earth’s surface. The farther the satellite is from the earth’s surface, the lesser will be its speed.
2. The orbital speed of a satellite does not depend on its mass. Satellites of different masses in orbits of the same radius will have the same speed.
Note: The orbital speed of a satellite revolving very close to the earth’s surface is about 8 km/second.
Period of Revolution of a Satellite : The time taken by the satellite to revolve around the Earth in its orbit is called its period of revolution.