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Gravitation Complete ChapteršŸ”„| CLASS 9th Science| NCERT covered | Prashant Kirad

Exphub 9th &10th惻2 minutes read

Prashant Bhaiya highlights the importance of studying the chapter on Gravitation for transforming lives, covering topics like Newton's gravity, centripetal force, and gravitational constant. The text explains key concepts such as Earth's movement, mass affecting gravity, and the relationship between pressure and area in physics.

Insights

  • Newton's Law of Gravitation states that the force between two bodies is directly proportional to their masses and inversely proportional to the square of the distance between them, crucial for calculating gravitational forces.
  • Pressure is defined as force divided by area, with sharp knives and wide straps exemplifying how area affects pressure, impacting various objects' functionality and comfort.

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Recent questions

  • What is the Universal Gravitational Constant?

    6.67 x 10^-11

  • How does mass affect the force of gravity?

    Determines gravitational force

  • What is the relationship between gravitational force and distance?

    Inversely proportional

  • How does Earth's movement depend on mass?

    Not size

  • What is the significance of centripetal force in circular motion?

    Balances gravitational force

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Summary

00:00

"Gravitation: Study, Practice, Life Changes"

  • Prashant Bhaiya emphasizes the importance of studying and practicing the chapter on Gravitation for significant life changes.
  • The study session will cover topics like Bion's Archimedes' Principle and numericals in a fun and engaging manner.
  • Newton's discovery of gravity is discussed, starting with the apple falling on his head.
  • Gravity is explained as a force of attraction between two bodies, unlike other forces of attraction.
  • The gravitational force keeps planets in orbit around the sun due to the attraction between them.
  • Newton's Law of Gravitation states that the force between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
  • The Universal Gravitational Constant, with a value of 6.67 * 10^-11, is crucial for calculating gravitational forces.
  • The unit of the gravitational constant is derived by combining the units of force, mass, and distance.
  • The concept of centripetal force is explained as the force that keeps objects in circular motion balanced with gravitational force.
  • Centripetal force is illustrated using the example of a stone tied to a rope and swung in a circle, emphasizing the balance of forces.

12:22

Mass Determines Gravity: Earth's Movement Explained

  • Earth's movement depends on mass, not size
  • Mass determines the force of gravity
  • Force of gravity inversely proportional to distance between objects
  • Halving the radius quadruples the force of gravity
  • Calculating gravitational force involves mass, distance, and gravitational constant
  • Gravitational force between two bodies with masses of 80kg and 200kg separated by 6 meters
  • Gravitational force calculation involves multiplication and division
  • Gravitational force unit is Newton
  • Gravitational force between Earth and a 1kg object at a distance of Earth's radius
  • Acceleration due to gravity is 9.8m/s^2 or approximately 10m/s^2

24:41

Gravitational Constant and Acceleration Explained

  • Gravitational constant is universal and constant at 6.67 x 10^-11.
  • The value of the gravitational constant remains the same, unlike friendships that can change.
  • Changes in altitude affect gravitational acceleration due to gravity.
  • Gravitational acceleration decreases as altitude increases.
  • Gravitational force decreases as distance from the center of the Earth decreases.
  • The shape of the Earth affects gravitational acceleration, with higher values at the poles and lower values at the equator.
  • Acceleration due to gravity is higher at the poles and lower at the equator.
  • Weight and mass are distinct concepts, with weight being the force of gravity acting on an object.
  • Weight is measured in Newtons, while mass is measured in kilograms.
  • Mass is a scalar quantity, while weight is a vector quantity with direction.

37:10

Weight and Gravity: Calculations and Comparisons

  • Weight cannot be zero, but it may be zero on a planet with no gravity inside.
  • If acceleration due to gravity is zero, weight will also be zero.
  • Mass remains constant regardless of location, but weight changes due to gravity's acceleration.
  • If Earth's diameter is halved, the radius will also be halved.
  • Quadrupling mass while halving the radius results in weight increasing 16 times.
  • Weight on a new planet with quadrupled mass and halved radius will be 16 times higher.
  • To calculate weight on a new planet, use the formula g = GM/R^2.
  • The weight of an 80 kg man on the Moon's surface is 400/3 Newtons.
  • Mass remains constant whether on Earth or the Moon.
  • Free fall occurs when an object falls due to gravity without external force.

49:28

Falling objects and planetary motion explained.

  • Remember the sign convention: negative for things coming down, positive for going up.
  • Focus on positive things and ask more questions.
  • Consider a stone free-falling from a building.
  • Analyze the horizontal velocity of a stone thrown from one building to another.
  • Determine which stone will hit the ground first.
  • Understand the impact of velocity direction on falling objects.
  • Calculate the final velocity of a car falling off a ledge.
  • Find the average speed of the car during the fall.
  • Determine the height of the ledge from the ground.
  • Explore Kepler's Laws, focusing on planetary motion and orbits.

01:02:17

"Pressure and Thrust: Forces in Action"

  • Thrust is a force that acts perpendicular upwards, causing objects like balloons to rise.
  • Pressure is defined as thrust acting on unit area, measured in Pascal.
  • Pressure is force divided by area, with the SI unit being Pascal.
  • Sharp knives cut better than blunt ones due to increased pressure from reduced area.
  • Wide straps on school bags reduce pressure on shoulders, making them more comfortable to carry.
  • Nails are sharpened to increase pressure when hitting objects with a hammer.
  • Camels have broad feet to reduce pressure on sand and mud, allowing for easier walking.
  • Tractor wheels are broad to reduce pressure on mud, enabling movement.
  • Pressure in fluids depends on depth and density, affecting objects' buoyancy.
  • Objects float or sink in fluids based on the pressure exerted by the liquid.

01:14:51

"Depth, Density, and Buoyancy in Fluids"

  • Greater depth of water results in increased pressure
  • Pressure increases with depth and depends on liquid's density
  • Density of liquid determines if objects float or sink
  • Objects float on denser fluids due to higher density
  • Pressure and ability to float depend on depth and density
  • Biot force is the upward force exerted on objects in fluids
  • Biot force is equal to the weight of fluid displaced by the object
  • Volume of an object determines the amount of fluid displaced
  • Archimedes' principle explains buoyancy based on displaced fluid's weight
  • Submarines adjust water levels to control buoyancy and floatation

01:28:05

Buoyancy, Displacement, and Gravitational Forces

  • Density of water affects object's buoyancy
  • Ship floats due to displacement of water
  • Archimedes' Principle explains buoyant force
  • Weight on Earth vs. weight on Moon
  • Gravitational constant and force between bodies
  • Pressure and area relationship in physics
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