This slide includes topics related to Newton's law of gravitation,gravity,acceleration due to gravity,freefall, weightlessness, mass and weight

1. Grade 10
Force Prepared by Bhuvan Acharya
Push or pull of an object is considered a force.
Push and pull come from the objects
interacting with one another. Terms like
stretch and squeeze can also be used to
denote force.
In Physics, force is defined as:
The push or pull on an object with mass that
causes it to change its velocity.

2. Common symbols: F→, F
SI unit: Newton
In SI base units: kg·m/s2
Other units:
dyne, poundal, pound-
force, kip, kilo pond
Derivations from other
quantities:
F = m a
Dimension: LMT-2
Common symbols: F→, F
SI unit: Newton
In SI base units: kg·m/s2
Other units:
dyne, poundal, pound-
force, kip, kilo pond
Derivations from other
quantities:
F = m a
Dimension: LMT-2
The Force can be measured using a spring balance. The SI unit of force is Newton(N).
Test your Knowledge o

3. Test your Knowledge on Force
Which of the following forces is responsible for
making the moon revolve around the Earth?
• A)Magnetic Force
• B)Electric force
• C)Frictional Force
• D)Gravitational Force

4. Which of the following statements is
true about force?
• A)Force is the push or pull on an object resulting
from the object's interaction with another object.
• B)Force is defined as mass per unit volume.
• C)Force is the ability to do work.
• D)The movement of charged particles is known as
force

5. Gravitation
• The force between any two bodies is called
gravitation.
• Before 1542AD, The earth is considered to be
the centre of solar system.This earth centered
model of the solar system is called geoentric
or ptolemaic model.
• In 16th century Nicholas Copernicus , put
forward heliocentric model in which The Sun
was the head of solar system.

6. Geocentric Model

7. Heliocentric Model

8. Newtons law of Gravitation
Newton’s Law of Gravitation states that “The
force of attraction between the two bodies is
directly proportional to the product of their
masses and inversely proportional to the square
of the distance between their centers.”This law
was formulated in 1687 AD.

9. Sir Issac Newton

10. Verification of Newton’s law:
Consider the two bodies of the mass M1 and M2with force F acting between
them towards their centre. If the distance between their centers is d then,
• According to Newton’s universal law of gravitation,
We have F ∝ m1m2……1) and
F ∝ 1/d2……… 2)
Combining 1 and 2 we get
𝑜𝑟, 𝐹 ∝
𝑚1𝑚2
𝑑2
Or,𝐹 = 𝐺
𝑚1𝑚2
𝑑2
• Where G is proportionality constant which is known as universal
gravitational constant.

11. Definition of G
• We have ,
• 𝐹 =
𝐺𝑚1𝑚2
𝑑2
• If m1=m2 =1kg and d= 1m.Then
• 𝐹 =
𝐺1𝑋1
12
• 𝐹 =G
• The universal gravitational constant can be
defined as the force of gravitation produced
between two bodies of unit mass each which are
separated unit distance apart.

12. Properties of G:
• Value of G is independent of the temperature,
pressure, nature of the intervening medium
and chemical composition of the masses of
the bodies.
• The numerical value of gravitational constant
(G) is 6.67x10-11 and
• Its unit is Nm2/Kg2

13. Newton’s law of gravitation is called
universe law ,why?
Newton’s law of the gravitation holds true or
applicable for all the objects present in this
universe whether the objects be terrestrial or
celestial. The gravitational force exists
everywhere in this universe. Therefore Newton’s
law of gravitation is called universe law.

14. To Know the relation between gravitational force
, mass and distance.
Sol. Let us consider two bodies of masses m1 and m2 which are kept d
distance apart. Then the gravitational force between them is given by
F=
𝐺𝑚1𝑚2
𝑑2
If masses of each are doubled then
Fnew=
𝐺2𝑚1𝑥2𝑚2
𝑑2
=
4𝐺𝑚1𝑚2
𝑑2
=4F
Therefore the new gravitational force increases by 4 times when mass of one
body is doubled.

15. Q.N 2. What Change occurs to the gravitational force between two body
when masses of each body doubled keeping distance constant?
Sol. Let us consider two bodies of masses m1 and m2 which are kept d distance
apart. Then the gravitational force between them is given by
F=
𝐺𝑚1𝑚2
𝑑2
If masses of each are doubled and distance is kept constant.
Fnew=
𝐺2𝑚1𝑥2𝑚2
𝑑2
=
4𝐺𝑚1𝑚2
𝑑2
=4F
Therefore the new gravitational force increases by 4 times when mass of one
body is doubled.

16. Q.N 2. What Change occurs to the gravitational force between two body
when masses of each doubled and distance tripled?
Sol. Let us consider two bodies of masses m1 and m2 which are kept d distance
apart. Then the gravitational force between them is given by
F=
𝐺𝑚1𝑚2
𝑑2
If masses of each are doubled and distance is tripled.
Fnew=
𝐺2𝑚1𝑥2𝑚2
(3𝑑)2
=
4𝐺𝑚1𝑚2
9𝑑2
=
4
9
F
Therefore the new gravitational force decreases by 4 times when mass of one
body is doubled and distance is tripled.

17. Importance of gravitational Force
• Binding all terrestrial objects.
• Holding the atmosphere on the planets.
• Rainfall and snowfall .
• Flow of water in river
• Motion of the planets in their respective
orbits.

18. Characteristics of gravitational force
• It is independent of the nature of intervening
medium.
• It is independent of presence or absence of
other bodies.
• It is independent of the nature and size of the
bodies.
• It is central force and acts along the line
joining the centres of two bodies.

19. Numericals
• .Mass of Earth is 6x1024 kg and mass of the Sun is
2x1030 kg and the distance between them is
1.5x1011
m. Calculate the gravitational force
between them.
• .Mass of Earth is 6x1024 kg and mass of the moon
7.1x1022 kg and gravitational force between them
is 1.682x1020 N ,find the distance between them.

20. Gravity

21. Gravity
• Gravity is a special case of gravitation.
• The force with which the earth pulls a body
towards its centre is called Gravity.
• F=
𝐺𝑀𝑚
𝑅2
• Its SI unit is Newton.

22. Comparison of gravity of different planets
• The gravity of the moon is 1/6th of the earth.
• The Jupiter is the largest planet of the solar
system.The mass of the Jupiter is about 319
times greater than the earth and radius is 11
times more than the earth.The gravity of the
Jupiter is 2.5 times more than the earth.

23. Acceleration due to gravity
• The acceleration produced on a body due to
gravity is called acceleration due to gravity.
• Its SI unit is 𝑚
𝑠2.
• The acceleration due to gravity on the moon is
1.66m/s2. What does it mean?

24. Coin and Feather experiment
• Galileos arguments were experimentally tested by the British
Scientist Robert Boyle. Boyle performed an experiment to verify
Galileos idea that a light object and heavy object fall together in
vacuum.
• Conclusion of the coin and feather is that the acceleration produced
in the freely falling objects is same and does not depend on the
masses of the falling objects.

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29. Home assignment
1)The radius of the moon is 1.17𝑥106
m and its mass is 7.2𝑥1022
kg. What is the gravity of the moon on
the body with mass 1kg?
2) The radius of the Earth is 6.4𝑥106
m and its mass is 6𝑥1024
kg. What is the acceleration due to
gravity of the earth.
3)What is the relationship between acceleration due to gravity of any planet with their radius?
4)Write the average value of acceleration due to gravity on the earth, moon and Jupiter.
5) The acceleration due to gravity on the earth is 9.8m/s2. What does it mean?
6)If your weight is 600N on earth, how far should you go from the centre of the earth so that your
weight will be 300N.(radius of the earth is 6.4x106m)
7)The mass of earth is 6x1024 kg and radius is 6.4x106m.Calculate the value of acceleration due to
gravity of the earth.
8)The mass of eath is 6x1024 kg and radius is 6.4x103km.Calculate the value of acceleration due to
gravity at the top of Mt Everest .Also calculate weight of a body having 80 kg.
9)The value of acceleration due to gravity on the surface of the earth is 9.8m/s2.Calculate the value of
acceleration due to gravity at the top of 1000Km from the earth surface.
10)A stone dropped freely from 72m height of the tower and reaches the ground in 6 seconds .
Calculate acceleration due to gravity of that stone.

30. Comparison of mass and weight
Mass
• The quantity of matter contained in a
body.
• It is scalar.
• Its SI unit is kg.
• It is constant everywhere.
• It can not be zero.
• it depends on no. of molecules and
their mass.
• It is measured with the help of beam
balance.
Weight
• The force with which the body is attracted
towards the center of the earth.
• It is vector.
• Its SI unit is Newton.
• Its value changes with the change of value of
g.
• It may be zero.
• It depends on value of g and mass.
• It is measured with the help of spring
balance.

31. Freefall
• The motion of a body under the influence of gravity alone is
called freefall
• Freefall occurs only in vacuum.
• Fall with Parachute
• Air exerts resistance on a parachute as a result it falls
slowely and a person with parachute can jump safely from
a greater height on the earth.But this is not possible on the
moon because there is no air and air resistance.

32. Weightlessness
• The state of a body in which the weight of a body becomes
zero is called weightlessness.
• The state of weightlessness can be observed in the
following cases.
1.Body in a freely falling lift.
Because the lift moves
down with acceleration
equal to acceleration
due to gravity i.e.,a=g
W=m(g-a)
=m(g-g)
=0

33. 2.Body in a satellite orbiting earth
• When a satellite is revolving around the earth,
every object inside the satellite has
acceleration equal to the acceleration due to
gravity.

34. 3.Body at null point
• At the null point force of moon and earth are
equal and opposite. And value of acceleration
due to gravity is also zero so weight is zero at
null point.

35. 4.Body at the center of the earth.
• At the center of the earth value of
acceleration due to gravity is zero so weight
becomes zero.

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38. Verification of Newtons law of
gravitation

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