The phenomenon of gravitational force was discovered by Sir Isaac Newton looking an apple falling from a tree on the ground and found the direction of the falling apple is vertically downward.
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| Gravitation |
When we throw a stone vertically upward, it falls vertically downward on the earth. Why?
- Constant downward pull:
- Influence of "g" force:
Why do High and Low tides occur at different times and different places?
- Moon's "g" force:
- 90 degree:
The moon and the artificial satellite do not fall on the earth. why?
- Two stationary objects attract each other because of the gravitational force.
- Similarly, the Earth and the moon attract each other, but the moon and the artificial satellite orbiting the earth.
- Because of the velocity of the moon and the satellite along their orbits, they do not fall on the earth.
- The work of the moon is zero that means:
- work = fs cos@ and cos@ / 90° = 0
- This means that the force is 0 then work also zero, therefore, the moon and artificial satellite do not fall on the earth.
"When an object is thrown upward, its velocity decreases and becomes zero after reaching a certain height." Why?
- The object's maximum height depends on its initial velocity.
- The higher the initial velocity, the object will oppose the gravity of the earth more, and the larger will be the height
- The velocity of an object decreases because of the force pulling an object vertically downward towards the centre of the earth and the final velocity becomes zero at a certain height.
"The object to be free from the gravity of the earth has to reach infinite distance from the earth." Why?
- An object going vertically upward from the surface of the earth having an initial velocity equal to the escape velocity to escape the gravitational force of the Earth.
- The force of gravity being inversely proportional to the square of the distance becomes zero only at an infinite distance from the earth.
- Total energy= kinetic energy + potential energy = [-GMm/infinite distance] = 0
"The value of g decreases as we go deep inside the earth." Why?
- When we go deep inside the earth towards the centre of the earth, the part of the Earth which contributes towards the gravitational force field by the object also decreases.
- This means that the value of M also decreases and as a combined result of the change in "r" and "M" the value of g decreases as we go deep inside the earth.
Why do we see falling star in the sky?
- Any celestial body moves under the influence of the force of gravity of the earth, it enters into the atmosphere.
- Because of friction and the buoyant force of an atmosphere, the celestial body has tremendous energy and get fired.
- We see this celestial body falling on the earth surface, either completely burns it or partially burn it is called "a falling star" at night.
Why do a feather and stone not reach the earth at the same time?
- When we drop a feather and heavy stone at the same time from a height the feather experiences a buoyant force and frictional force due to air.
- Therefore it floats and reaches the ground slowly. The buoyant and frictional force on the stone is much less than the weight of the stone and it does not affect the speed of the stone.
- But if this experiment we do in a vacuum then both reach the earth at the same time.
"The value of "g" is not the same everywhere on the surface of the earth." why?
- The shape of the earth is not exactly spherical. It bulges at the equator and the flatter at the poles.
- There was the distance of a point on the surface of the earth from the centre disperse somewhere from place to place.
- So the value of "g" is highest as 9.832 m/s^2 at the poles and it is the lowest 9.78 m/s^2 at the Equator and decreases slowly with decreasing latitude.
"The value of "R" increases, then the value of "g" decreases."
When we reach the typical heights, the value of "g" decreases. Why?
- The value of "g" decreases with increasing heights and at an infinite distance from the earth because of the Universal Gravitation Law.
- "every object attracts each other with a definite force and directly proportional to the product of the masses of the two objects and is inversely proportional to the square of the distance between them as in the formulae: g = -GM/r^2
- For example, the change in the value of "g" due to the large change in the value of the satellite from the centre of the earth. The height of a typical weather satellite is 400 km. and the value of "g" is 8.7 m/s^2 as compared to the height of a communication satellite is 35700 km and the value of "g" is 0.225 m/s^2.
The object will not fall back on the earth at a certain height. Why?
- The value of "g" keeps decreasing as an object goes higher and higher and therefore the force pulling an object vertically downward decreases.
- When we increase the initial velocity, an object is able to overcome the downward pool by the earth with a particular value of the initial velocity of an object and can escape the Earth forever and will not fall back on the earth.
Space traveller and objects in spacecraft appear to be floating. Why?
- The value of 'g" is only 11 % less than its value on the surface of the earth in the space station.
- The weightlessness of spacecraft, travellers, objects, etc. is caused by their being in the state of free fall. Because the only gravitational force acting on it.
- The spacecraft is not falling on the earth because of its velocity along orbit.
