Variation in value of g :
A. Change along the surface of the earth :
- Value of g is not the same everywhere on the surface of the earth.
- Reason- shape of the earth is not ex-actly spherical.
- The distance of a point on the surface of the earth from its centre differs somewhat from place to place.
- Due to its rotation, the earth bulges at the equator and is flatter a t the poles.
- Its radius is largest at the equator and smallest at the poles.
- The value of g is thus highest (9.832 m/s²) at the poles and decreases slowly with decreasing latitude.
- It is lowest (9.78 m/s²) at the equator.
B. Change with height :
- As we go above the earth’s surface, the value of r increases and the value of g decreases.
- However, the decrease is rather small for heights which are small in comparison to the earth’s radius.
C. Change with depth :
- The value of g also changes if we go inside the earth.
- The value of r decreases and one would think that the value of g should increase as per the formula.
- However, the part of the earth which contributes towards the gravitational force felt by the object also decreases.
- Which means that the value of M to be also decreases.
- As a combined result of change in r and M, the value of g decreases as we go deep inside the earth.
- On the moon it is about 1/6th of the value on the earth.
Mass and Weight :
Mass :
- Mass is the amount of matter present in the object.
- SI unit - kg.
- Scalar quantity.
- Its value is same everywhere.
- According to Newton’s first law, it is the measure of the inertia of an object.
- Higher the mass, higher is the inertia.
Weight :
- It is defined as the force with which the earth attracts the object.
- The force (F) on an object of mass m on the surface of the earth can be written as
Gravitational waves :
- Astronomical objects emit these waves.
- All our knowledge about the universe has been obtained through these waves.
- Are a very different type of waves.
- Also called the waves on the fabric of space-time.
- Einstein predicted their existence in 1916.
- Are very weak
- Very difficult to detect them.
- Scientists have constructed extremely sensitive instruments to detect the gravitational waves emitted by astronomical sources.
- Among these, LIGO (Laser Interferometric Gravitational Wave Observatory) is the prominent one.
- Exactly after hundred years of their prediction, scientists detected these waves coming from an astronomical source.
- Indian scientists have contributed significantly in this discovery.