Gravitation Class 9 Science | CBSE | NCERT | Universal law of Gravitation

Summary

This video explains the concept of gravitation for Class 9 students, covering the fundamental force that attracts objects with mass. The speaker discusses how gravitational force operates between Earth and other objects, like the Moon's orbit around Earth and the Earth's orbit around the Sun. Key concepts such as the Universal Law of Gravitation, gravitational constant, and inverse square law are introduced. The video also highlights the importance of gravitational force in real-world applications like tides and objects falling to the ground. Through clear explanations and relatable examples, the content makes complex concepts accessible to students.

Takeaways

• 😀 Gravitational force is the attractive force between two objects that have mass. Every object in the universe pulls on every other object.
• 😀 The Moon revolves around the Earth because of the gravitational pull exerted by the Earth, but it does not fall onto the Earth due to centripetal force.
• 😀 The Earth pulls all objects towards itself, which is why objects fall back to the ground when thrown. This force is known as gravitational force.
• 😀 Gravitational force is stronger when the masses of the objects involved are greater and weaker when the distance between them is larger.
• 😀 Sir Isaac Newton discovered gravitational force after observing the falling of an apple, leading to the formulation of the Universal Law of Gravitation.
• 😀 The Universal Law of Gravitation states that every object in the universe attracts every other object with a force proportional to their masses and inversely proportional to the square of the distance between them.
• 😀 Gravitational force is dependent on two main factors: mass of the objects and the distance between them.
• 😀 The gravitational constant (G) is a key factor in the Universal Law of Gravitation and has a fixed value of 6.7 × 10^-11 N·m²/kg².
• 😀 Gravitational force is always an attractive force, never a repulsive one, and it is responsible for phenomena like tides in the oceans.
• 😀 Gravitational force acts as the reason for all planetary movements, including the Earth's revolution around the Sun and the Moon's revolution around the Earth.
• 😀 Gravitational force has many practical applications, such as causing objects to fall to the ground and influencing tides caused by the Moon and Sun's gravitational pull.

Q & A

What is gravitational force?

Gravitational force is the invisible force that attracts objects toward each other. It is responsible for pulling objects towards the Earth, causing things to fall when dropped.

Why does the Moon revolve around the Earth but not fall onto it?

The Moon revolves around the Earth due to Earth's gravitational pull. However, the Moon does not fall because its orbital speed creates a balance with the gravitational pull, resulting in a continuous orbit rather than a fall.

What is the relationship between the masses of objects and gravitational force?

Gravitational force is directly proportional to the masses of the two objects. The larger the masses, the stronger the gravitational force between them.

What role does distance play in gravitational force?

Gravitational force is inversely proportional to the square of the distance between two objects. This means that as the distance between objects increases, the gravitational force between them decreases.

What is the formula for calculating gravitational force?

The formula for gravitational force is: F = G × (M × m) / d², where F is the gravitational force, G is the gravitational constant, M and m are the masses of the objects, and d is the distance between them.

What is the gravitational constant, and what is its value?

The gravitational constant (G) is a fundamental constant used in calculating gravitational force. Its value is 6.7 × 10⁻¹¹ N·m²/kg².

What are the key properties of gravitational force?

The key properties of gravitational force are: it is always attractive, it is a relatively weak force compared to other forces, it is independent of the medium in which objects exist, and it follows the inverse square law.

Why don't we observe small objects pulling on us with gravity?

Small objects have much weaker gravitational forces compared to larger objects like Earth. Since Earth's gravitational force dominates, we don't notice the weaker pulls of smaller objects on us.

How does the gravitational force between the Earth and the Moon affect ocean tides?

The gravitational pull between the Earth and the Moon causes the ocean tides. The Moon's gravity pulls on Earth's oceans, creating high and low tides.

How does gravitational force affect the orbits of planets?

Gravitational force from the Sun pulls the planets towards it, keeping them in orbit. This gravitational force ensures that planets revolve around the Sun instead of flying off into space.