What is gravitation?
The tendency of bodies to move towards each other is called gravitation.
The motion of planets around the Sun has always been a subject of curiosity for centuries. Earlier scientists believed that planets moved in circular paths, but careful observations led to a more accurate understanding. The force of attraction was first observed by Sir Isaac Newton and was presented as Newton’s law of gravitation in1680.
However, gravitation can generally exist in two main instances:
- An attraction of objects by the Earth. This means that if an object is thrown upwards, it reaches a certain height and falls downwards because of the gravity of the Earth.
- The attraction of objects in outer space. That is, the force of attraction between the other planets and the Sun.
Difference between Gravity and Gravitation
- Gravity is the actual force experienced by any object under the influence of any other object in its gravitational field.
- Gravitation is defined as the phenomenon that any two masses attract one another.
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Get Expert GuidanceWhat Is Gravitational Force?
Each body in the universe attracts other bodies towards itself with a force known as Gravitational Force. Thus, gravitation is a study of the interaction between two masses. Out of the two masses, the heavier one is called the source mass, and the lighter one is called the test mass.
Gravitational force is a central force which depends only on the position of the test mass from the source mass and always acts along the line joining the centres of the two masses.
What is the Centre of Gravity?
The Centre of gravity is a theoretical point in the body where the body’s total weight is thought to be concentrated. It predicts the behaviour of a moving body when acted on by gravity. This concept is also applied in designing static structures such as buildings and bridges. In a uniform gravitational field, the centre of gravity is identical to the centre of mass. Yet, the two points do not always coincide.
Difference between Centre of mass and Centre of gravity?
Many students often get confused about centre of mass and centre of gravity, so let’s have a look at it. The centre of mass is a point at which the mass distribution is equal in all directions, and it doesn’t depend upon the gravitational field. The centre of gravity is a point in an object where the distribution of weight is equal in all directions, and it does depend on the gravitational field. But it’s important to understand that an object’s centre of mass and centre of gravity lie at the same point in a uniform gravitational field.
Energy
Energy is the capacity of a body or system to do work. It exists in many forms, such as kinetic, potential, thermal, electrical, chemical, and nuclear energy. Since this chapter is about Gravitation, we will be mainly focusing on Kinetic and potential energy, and you could read more about it in the section given below:
1. Kinetic Energy
Kinetic energy refers to the energy possessed by an object due to its motion. It depends on both the object’s mass and its velocity of the object—the greater the mass or the faster it moves, the higher its kinetic energy. In simple terms, anything that is moving possesses kinetic energy.
Kinetic Energy Formula
Suppose an object of mass ‘m’ moves with a velocity of ‘v’ then the formula used to calculate the kinetic energy of the object is: K.E = 1/2 mv2
2. Potential energy
Potential energy is the stored energy in an object or system based on its position, condition, or arrangement. It represents the energy an object holds that can be released or transformed into other forms when its position or state changes.
Formula of Potential Energy
The potential energy of a body depends on the force acting on it and its displacement. For gravitational force, the potential energy is given by: PE = mgh
Where:
- m is the mass of the body.
- g is the acceleration due to gravity.
- h is the height of the body above the reference level
Newton’s Law of Gravitation
According to Newton’s law of gravitation, every particle in the universe attracts every other particle with a force whose magnitude is,
- Directly proportional to the product of their masses: F ∝ (M1M2)
- Inversely proportional to the square of the distance between their centre: (F ∝ 1/r2)
- On combining equations 1 and 2, we get,
Or, f(r) = GM1M2/r2 [f(r) is a variable, non-contact, and conservative force]
As f(r) varies inversely as the square of ‘r’, it is also known as the inverse square law force. The proportionality constant (G) in the above equation is known as the gravitational constant.
Note: The dimension formula of G is [M-1L3T-2].
In this chapter, you will learn more about Earth’s gravity and other subdivisions of it.
FAQ's
The gravitational force between two masses is given by F = GM₁M₂/r².
The gravitational constant G has a value of approximately
6.67 × 10⁻¹¹ N m² kg⁻².
Objects fall towards the Earth because it exerts a gravitational force of attraction on them.
Yes, gravitational force is directly proportional to the product of the two masses.
Astronauts experience apparent weightlessness because they and the spacecraft are in continuous free fall under Earth’s gravitational force.
Yes, it is an important chapter because it encompasses many equations associated with numerous gravitational concepts