Page 5 - Force 10

Unit 1: Gravitational force cont…… 2

Free-fall: If an object falls freely towards the W =m * 0 , ∴ W = 0
center of planet or satellite without any resistance,
due to the effect of gravity is called free-fall. What will happen when a feather coin
During free-fall, Acc. due to gravity = experiment is done on earth surface?
Acc. present in the object.  They don’t undergo free-fall due to the air
Weightlessness: The condition at which the resistance. The feather will experience more
object losses its weight completely due to either magnitude of air resistance than the coin due
free-fall or absence of the gravity is called to its broad surface & less weight. Then it
weightlessness. Or reaches the ground later than coin.
It is the state in which the body experiences When a man jump from the parachute on the
that the body is not being attracted by any force. earth, safe landing is possible.
➥ A satellite doesn’t need any energy to remove  When a man jumps from a significant height
around the earth. The gravitational force with parachute, the umbrella of the parachute
between the earth and the satellite is balanced opens and air resistance acts totally upon it.
by the outward centrifugal force created by This reduces the acceleration and becomes
velocity and inward force created by the nearly equal to zero. Then the parachute falls
centripetal force due to the force of gravity. with uniform velocity & the final velocity

➥ As we know, = becomes very less. Thus, safe landing is
2
∴ ∝ 1 possible.
2 When a man with parachute jumps on the
➥ In case of earth, radius is more at equator than lunar surface, serious accident will occur?
pole. As the radius increase the gravity  When a man jumps with parachute on lunar
decrease. So, acceleration due to gravity is surface, it undergoes free-fall due to the
more at pole than equator. absence of air resistance. The acceleration
➥ At center, g is zero because the effective mass produced in the parachute becomes equal to
of earth is also zero. the acceleration due to the gravity of the
➥ A person falling through the parachute lands moon. Due to this, final velocity of parachute
safely because air upthrust acts on the becomes too greater & serious accident will
parachute & retards its acceleration. So, it falls occurs.
with the uniform velocity. Weightlessness due to Weightlessness due to
➥ A person hurts badly while falling from a free-fall absence of gravity
significant height because the time period to It occurs inside the It occurs outside the
reach the ground increases & the final velocity gravitational field of gravitational field of

increases. As we know, v ∝ t ( v = u + gt ) planet. planet.
Thus, serious accident occurs. The condition at which The condition at which

➥ The weight of free falling object is zero object loses its weight object loses its weight
because the acceleration due to gravity (g) of completely while completely when no
planet or satellite is equal to the acceleration falling towards the force of gravity acts to
produced in the free falling object (g’). center of the planet it.
We know, W = m (g-g’) without any air
When an object is falling freely, g = g’ resistance.

Do you know?
Henry Cavendish determined the value of G experimentally for the first time by using a sensitive ( torsion)
balance.