Explaining gravity.

1. Why Gravity is Different on
Earth and Moon
By Thomas Down

2. Topics Covered...
● Man and the Moon
● What is Gravity
● Formula of Gravitational
Force
● Why objects weigh less
on Moon
● Difference between
Earth’s and Moon’s
gravity

3. Man and the Moon
● Man’s fascination with the moon started a long, long time ago when the first man spotted a glowing
white orb illuminating the night sky.
● Ever since then, the moon has been an important part of our folklore and mythologies.
● In the 20th century, man’s obsession with the moon reached a new peak when Neil Armstrong
became the first man on the moon.
● Today, you can even buy a piece of land on the moon. In future, we might even colonize the moon!

4. What is Gravity
● Newton is considered to be the ‘Father of Gravity’. We all know about the famous story of an apple
falling on Newton that fuelled his research about gravity. So what is gravity?
● Gravity or gravitational force is a force attraction between any two objects. Depending upon the
mass of the objects and the distance between them, the force of attraction may vary.
● If the mass of an object is enormous then the gravitational force with which it attracts another object
close to it will be great, and vice versa.

5. Formula of Gravitational force
The gravitational force between two objects can be calculated by using the formula:
F= G (M1 x M2)
_____________
r2
Where F = Force of gravity/Gravitational Force
G = Gravitational Constant. The value of G is always 6.673×10-11 N m2 kg-2
M1 = Mass of first object
M2 = Mass of second object
r = distance between the centres of two objects

6. Why objects weigh less on the
Moon
If someone asks me tips for reducing body weight, I would jokingly suggest them to live on the moon. It is
a well-known fact that the weight of a person on the moon is considerably lesser to compared to his/her
weight on the earth. To understand why objects weigh lighter on moon compared to earth, we need to
know the difference between mass and weight.
It is to be noted that I mentioned the mass of the objects and not their weight while explaining gravity.
Mass is the amount of matter an object contains and it will remain constant whereas weight of an object is
the gravitational force with which the object is pulled down. Since the gravitational force of the moon is
lesser than that of the earth, objects weigh lighter on the moon. In space, astronauts experience the
phenomenon of weightlessness because there is no gravity to pull them down.

7. Difference between Earth’s and
Moon’s gravity
● It has been clearly established that the gravitational force of the earth is greater than that of the
moon. But why is there a difference between the earth and the moon’s gravity? The answer to this
question is fairly simple.
● We had learned earlier that force of gravity is directly proportional to the mass of the objects. When
you compare the earth’s mass with respect to the moon’s mass, you will find that the earth has a far
greater mass. Thus, the earth has greater gravitational pull compared to the moon.
● In conclusion, I would like to say that saving the resources on earth and preserving our planet is a
much simpler way to sustain human race than colonizing the moon or the mars! On that thought-
provoking note, I will take your leave!

8. Resources...
The following conversions occur frequently in physics and are very useful. (a) Use 1 mi = 5280 ft and 1 h =
3600 s to convert 60 mph to units of ft/s. (b) The acceleration of a freely falling object is 32
ft/s². Use 1 ft = 30.48 cm to express this acceleration in units of m/s². (c) The
density of water is 1.0 g/cm³. Convert this density to units of kg/m