In general term gravity is the force of attraction between two objects which have a definite mass or energy. For observing gravitational force these objects may be atoms, planets, or galaxies. In this article, we have mentioned about ‘what is gravity and gravitational force?‘
The word ‘gravity’ is taken from the Latin word ‘gravitas’ that’s meaning is ‘weight’. Though gravity is the weakest fundamental force of nature, so it is almost negligible for atoms but it plays an important role while considering large and massive bodies.
(“when you throw any objects up why does it come down, why doesn’t it go up for always…?” This is the most asked question for children in childhood by their relatives to judge their knowledge…Doesn’t it…? So here’s the answer who doesn’t know about it yet, it’s because of the gravity of earth. -Lol)
The term gravity and gravitational force both have different meanings but in general, we consider it the same. The attraction force between two objects is called gravitation force, these objects may be from anywhere in the universe.
While in the case of gravity, it is the force of attraction of a body towards the center of the earth. Gravitational force is the broad term used for the universe while gravity force is considered only on earth.
Gravity is the weakest fundamental force of nature. To define gravitation Scientists have described many times and still working to understand its behavior. Here we have mentioned two main theories to get it properly:
- Newton’s law of gravitation,
- Gravity by Einstein’s general theory of relativity.
(Read about- 4 Fundamental forces of nature)
Newton’s law of gravitation
In 1687 AD, Sir Isaac Newton gave a law which is also called the Universal law of gravitation and thus he first discovered the gravity.
(“should I tell you about the story of an apple falling down…?” Ok leave it, I think your judgemental-relatives or teacher has told you about it. -Lol)
The universal law of gravitation by Newton- “All bodies in the universe attract other bodies with a force that is directly proportional to their masses and inversely proportional to the square of the distance between them, and this force is called gravitational force.”
If we consider two bodies with their mass ‘m1‘ and ‘m2‘ and the distance between them is ‘r’, then we found two stats:
F ∝ m1 × m2
F ∝ 1/r2
⇒ F ∝ m1 × m2/r2
⇒ F=Gm1 × m2/r2
Here ‘G’ is a proportional constant also known as universal gravitational constant.
The mathematical value of universal constant, G=6.67 × 10-11 Nm2/kg2
Gravity by Einstein’s general theory of relativity
Though Newton’s law of gravity is applicable for the objects that move slowly compare to the speed of light. It gives the approximate value for the gravitational effect of any object. Whereas a theory given by Albert Einstein in 1915 describes the gravity more accurately, and this theory is known as “general theory of relativity”.
According to Einstein’s general theory of relativity, gravity is not a force, it is a space-time curvature caused by the mass of any object. This theory is mostly applicable to the gravitation of a body with high mass or density.
The mass of any object is the proportion of the space-time distortion. The objects with more mass distort the space-time more, whereas low mass object has low distortion and low gravity.
To know more about ‘how Einstein’s general theory of relativity explains the term gravity’, you can this link General theory of relativity by Einstein: Explained.
Acceleration due to the gravity of Earth
The gravitational force which is considered on earth is called gravity. Acceleration due to gravity is the pulling acceleration of a body due to the gravitational force of the earth.
This acceleration due to gravity is represented by a small letter ‘g’ and its value on the surface of the earth is 9.8m/sec2.
If we consider a small object is placed outside of the earth at some height and another object is the earth itself, then earth will start pulling this small object with acceleration due to gravity ‘g’.
The relation between weight and gravity
The weight of an object is equal to the gravitational force of the object towards the earth center or the weight of an object is the force of gravity on the objects if it is placed on the surface of the earth. So both the term weight and force of gravity are the same.
Case 1st- if the object is placed on the surface of the earth:
Weight = Force of Gravity
If a body of mass m is placed on the surface of earth then its weight, W=mg
and also the force of gravity, Fg=mg
where ‘g’ is the acceleration due to gravity.
Case 2nd- if the object is placed on the height of ‘h’ from the center of the earth:
Weight equal ≠ Force of Gravity
If a body of mass m is placed on any height from the earth surface, W=mg
And the force of gravity, Fg=G × Me × m/h2
Where ‘Me’ is the mass of the earth.
Weight is a variable term that depends on the value of acceleration due to gravity ‘g’.
Weight on Other Planets
The weight of any object depends on the value of ‘g’ and the value of ‘g’ also differs for each and every planet, whereas the mass of the body is always constant.
Here I have given a list of the value of ‘g’ on every planet with the respective weight considering the mass of any small body ‘m=10 kg’ which is placed on the surface of that planet.
|Planets||Value of ‘g’ in m/sec2||
Weight (W=mg) in N
|Mercury||3.7 m/sec2||37 N|
|Venus||8.87 m/sec2||88.7 N|
|Earth||9.8 m/sec2||98 N|
|Mars||3.71 m/sec2||37.1 N|
|Jupiter||24.79 m/sec2||247.9 N|
|Saturn||10.44 m/sec2||104.4 N|
|Uranus||8.87 m/sec2||88.7 N|
|Neptune||11.15 m/sec2||111.5 N|
The value of ‘g’ on the Moon is 1.62 m/sec2 and weight is 16.2 N if the mass of the body is 10 kg.