Question 1 What do you mean by the term free fall?
Question 2 During a free fall will heavier objects accelerate more than lighter ones?
Question 3 What do you understand by the term acceleration due to gravity of earth?
Question 4 What is the value of acceleration due to gravity?
Question 5 Is the acceleration due to gravity of earth g a constant?
Question 6 On what factors does the value of g depends?
The falling of a body from a height towards the earth under gravitational force is called Free fall.
Such a body is called freely falling body.
The earth attracts object towards it due to gravitational force.Whenever object fall towards the earth under this force, we say that object are in free fall.While falling there is no change in direction of motion of object but due to earth attraction, there will be a change in magnitude of the velocity.Any change in velocity involves acceleration.
Whenever an object falls towards earth,an acceleration is involved.
This acceleration is due to earth’s gravitation force.Therefore it is called as acceleration due to gravity.
It is denoted by g.
F = m x a
F = m x g
The acceleration of an object falling freely towards the earth does not depend on mass of object.During free fall,heavier as well as light objects accelerate at same rate.
For Ex:When a feather and coin are dropped from a roof, coin reaches the ground first and feather takes time.
Feather has large surface area and therefore experiences more resistance from air.Thus its speed decreases and reaches later.Coin has small surface area and therefore experiences less resistance from air.Thus its speed increases and reaches faster.If there was no air then feather and coin reaches the ground at same time.
The value of g is 9.8 m/s2
When an object falls on the ground under the action of earth’s gravity,i ts velocity increases at rate of 9.8 m/ s2.
When a body is dropped freely, it falls with an acceleration of 9.8 m/ s2
When a body is thrown vertically upwards, it undergoes retardation of 9.8 m/ s2
The value of g depends on
1) G(gravitational constant)
2) M(mass of earth)
3) d or r or R (radius of earth)
The value of g is not constant at all places on the surface of the earth.
The value of g is constant at a given place on the surface of earth.
The earth is not perfect sphere,so the value of its radius R is not the same at the places on its surface.
Since the radius of earth at the poles is minimum,the value of g is maximum at poles.
Since the radius of earth at the equator is maximum,the value of g is minimum at equator.
As we go up from the surface of earth, the distance from center of earth increases and hence the value of g decreases.
g=9.8 m/ s2 at an altitude of 200 km above the surface of earth.
g=7.3 m/ s2 at an altitude of 1000 km above the surface of earth.
The value of g is maximum on the surface of earth,it decreases on going above the surface of earth or on going inside the surface of the earth.
The value of g on the moon is about one-sixth of the value of g on the earth.
Equation of Motion for freely falling bodies
When a body is falling vertically downwards ,its velocity increases ,g=positive.
When a body is thrown vertically upwards,its velocity decreases ,g =negative.
When a body is dropped freely from height,u=0.
When a body is thrown vertically upward,v=0.