TLDR;
This video provides an in-depth explanation of gravity, covering the universal law of gravitation, its properties, acceleration due to gravity, and the concepts of mass and weight. It uses examples and questions to help viewers understand these concepts and their applications.
- Explains the universal law of gravitation and its formula.
- Discusses the properties of gravitational force, including its attractive nature and independence from the medium.
- Defines acceleration due to gravity and its direction towards the Earth's center.
- Differentiates between mass and weight, providing examples and calculations.
Introduction to Gravity [0:18]
The video starts by introducing the topic of gravity and its importance for the upcoming exams. It mentions that the discussion will cover the universal law of gravitation, acceleration due to gravity, and the difference between mass and weight. The intro uses the example of Newton's apple to illustrate the concept of gravity.
Universal Law of Gravitation [1:39]
The universal law of gravitation states that every object in the universe attracts every other object with a force. This force is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. The formula for gravitational force is F = G(m1m2)/r², where G is the gravitational constant. The video emphasizes that this attraction occurs between all objects with mass, not just large celestial bodies.
Properties of Gravitational Force [10:31]
Gravitational force is always attractive, unlike magnetic or electrostatic forces which can be repulsive. It is independent of the medium between the objects, meaning the force remains the same whether the objects are in air, water, or space. Gravitational force is the weakest of the fundamental forces, but it has a long range. It also acts as an action-reaction pair, where each object exerts an equal and opposite force on the other.
Why Moon Doesn't Fall on Earth [16:57]
The moon doesn't fall to Earth because it is constantly revolving around the Earth. The gravitational force between the Earth and the moon provides the necessary centripetal force for the moon's orbit. If the moon's velocity were to stop, it would indeed fall towards the Earth due to gravity.
Universal Law of Gravitation Question [20:55]
The video presents a question about the universal law of gravitation, asking between which objects the gravitational force exists. The correct answer is that it exists between all objects with mass in the universe. Another question explores how the gravitational force changes if the mass of two objects is halved. The answer is that the force becomes one-fourth of the original force.
Value of Parabola Question [27:01]
The video discusses the factors on which the ideal of gravity depends. The correct answer is that it depends on both the mass and radius of the Earth. It is independent of the mass and radius of the object experiencing the gravitational force.
Action Between Earth and Apple [28:26]
The video explains that the force of attraction between the Earth and an apple is equal in magnitude but opposite in direction. This is an example of Newton's third law of motion (action-reaction pair). While the forces are equal, the Earth's acceleration is negligible due to its large mass, whereas the apple's acceleration is significant and observable.
Specific Gravity Question [30:22]
The video addresses a question about how the force of gravity between two masses changes when they are placed in a liquid with a specific gravity. The answer is that the force remains the same because gravitational force is independent of the medium.
Earth Bound Atmosphere [31:58]
The Earth has an atmosphere because of its significant mass and resulting gravitational force, which attracts and holds atmospheric molecules. The moon, with its smaller mass and weaker gravitational force, cannot retain an atmosphere.
Acceleration Due to Gravity [33:26]
Acceleration due to gravity is the acceleration experienced by an object due to the force of gravity. It is always directed towards the center of the Earth. The video explains that even when an object is thrown upwards, gravity pulls it downwards, causing it to eventually fall back to the ground.
Acceleration to Gravity Direction [35:52]
The direction of acceleration due to gravity is always towards the center of the Earth and is independent of the mass of the object. In a vacuum, objects of different masses will fall with the same acceleration (9.8 m/s²). Freefall is defined as the motion of an object falling solely under the influence of gravity.
Equation of Acceleration Gravity [38:05]
The video derives the equation for acceleration due to gravity (g = GM/R²), where G is the gravitational constant, M is the mass of the Earth, and R is the radius of the Earth. This equation shows that acceleration due to gravity depends only on the mass and radius of the Earth and is independent of the mass of the falling object.
Acceleration Gravity Question [42:49]
The video presents a question about how acceleration due to gravity changes on another planet with twice the mass and twice the radius of Earth. By substituting these values into the equation g = GM/R², it is determined that the acceleration due to gravity on the other planet is half that of Earth.
Velocity and Acceleration Question [46:37]
The video discusses a scenario where objects of different masses are falling from the same height on the moon. The correct answer is that they will have the same velocity at every instant and experience the same acceleration. However, they will experience different forces due to their different masses.
Upaphos of Gravity [49:07]
When an object is thrown upwards, the force of gravity acts in the downward direction. The video emphasizes that gravity always pulls objects towards the Earth's center, regardless of the object's motion.
Acceleration Gravity Near the Moon Surface [50:18]
The acceleration due to gravity near the moon's surface is approximately one-sixth of that near the Earth's surface. This is because the moon has less mass than the Earth.
Maximum Acceleration Due to Gravity [52:06]
The maximum acceleration due to gravity occurs on the surface of the Earth. As you move away from the surface (either upwards or downwards towards the center), the acceleration due to gravity decreases. At the center of the Earth, the acceleration due to gravity is zero.
Weight Definition [53:50]
Weight is defined as the force exerted on an object due to gravity (W = mg). It is important to distinguish between mass and weight. Mass is a measure of the amount of matter in an object, while weight is the force of gravity acting on that mass.
Weight Question [57:30]
The video presents a question about finding the mass of a body with a weight of 49 Newtons. Using the formula W = mg, the mass is calculated to be approximately 5 kilograms. Another question asks about the weight of a body on the moon, given its weight on Earth. The weight on the moon is one-sixth of the weight on Earth.
Weight Scalar Quantity [59:56]
Weight is not a scalar quantity; it is a vector quantity because it has both magnitude and direction. Weight is also not a fundamental quantity.
Planet Mass Question [1:00:59]
The video concludes with a question about the weight of a 1 kg mass on a planet with twice the mass and three times the radius of Earth. The weight is calculated using the formula W = mg, where g is the acceleration due to gravity on the planet. The final answer is approximately 2.7 Newtons.