1. What is Gravity?
Gravity is the force with which the Earth pulls objects toward its center. It is a special case of the more general force called gravitation. While gravitation acts between any two masses anywhere in the universe, gravity specifically refers to the attraction between the Earth and objects near its surface.
Gravity is the reason objects fall when you drop them, why you stay firmly on the ground, and why the Moon remains in orbit around the Earth.
1.1. The Pull of the Earth
The Earth is massive. Because all masses attract each other, the Earth exerts a strong pull on everything around it. This pull gives objects weight and keeps the atmosphere, oceans, and living beings attached to the planet.
1.1.1. Everyday Observations
- A ball thrown upward always comes back down.
- Rain falls toward the ground.
- You feel heavier when carrying a heavy load because gravity acts on the load as well.
2. What is Gravitational Force?
Gravitational force is the attraction that exists between any two objects with mass. It does not matter whether the objects are small or large—this force always acts, although it becomes noticeable only when one object has a large mass (like the Earth).
Every object, including you, exerts gravitational force on every other object, but the force is extremely small unless the masses involved are huge.
2.1. Characteristics of Gravitational Force
- It is always attractive.
- It acts along the line joining the centers of the two masses.
- Its strength decreases as the distance between objects increases.
- It depends on the masses of both objects.
2.2. Examples in the Universe
- The Sun attracts the planets, keeping them in orbit.
- The Earth attracts the Moon.
- Galaxies stay bound together under gravity.
3. Why Don’t We Notice All Gravitational Forces?
Although every object pulls every other object, we usually only notice the gravitational force of massive bodies like the Earth. The gravitational force between two small objects (like a pen and a book) is extremely tiny and almost impossible to detect without sensitive equipment.
3.1. Mass Matters
The strength of the gravitational force increases with mass. This is why Earth's gravity is strong enough to hold everything down, while the force between small everyday objects is too weak to notice.
3.2. Distance Matters Too
Gravitational force decreases rapidly as the distance between objects increases. This is why you do not feel any noticeable pull from objects across a room—the distance makes the force very small.
4. Gravity as a Force Causing Motion
Gravity plays a key role in determining how objects move. When you drop an object, gravity accelerates it toward the ground. When planets orbit the Sun, gravity provides the necessary centripetal force to keep them moving in curved paths.
4.1. Gravity and Falling Bodies
Objects fall because gravity acts on them. Without gravity, objects would not fall—they would simply float away. Gravity gives them acceleration, causing their speed to increase as they fall.
4.2. Gravity in Orbital Motion
Satellites, moons, and planets are constantly falling toward the object they orbit, but they also move forward quickly. This combination keeps them in continuous orbit instead of crashing.
5. Why Understanding Gravity is Important
Gravity shapes the structure and behavior of the universe. It determines the motion of planets, the formation of galaxies, and even the tides on Earth. Understanding gravitational force is essential for explaining the world around us, studying astronomy, designing spacecraft, and exploring planetary motion.
In the next topic, we explore the Universal Law of Gravitation, which mathematically describes how gravitational force acts between two masses.