Kepler's Laws of Planetary Motion
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Questions and Answers

What is the value of g at the height of Mount Everest (8.8 km)?

  • 9.8 m/s² (correct)
  • 8.7 m/s²
  • 0.225 m/s²
  • 9.77 m/s²
  • How does the value of g change when you go deeper inside the Earth?

  • It decreases (correct)
  • It remains the same
  • It first increases then decreases
  • It increases
  • At what height is the value of g approximately 0.225 m/s²?

  • 8.8 km
  • 35700 km (correct)
  • 400 km
  • 36.6 km
  • What will be the value of g at the center of the Earth?

    <p>0 m/s²</p> Signup and view all the answers

    How does the mass of an object change when moving from Earth to the moon?

    <p>It remains the same</p> Signup and view all the answers

    Using the same amount of force, how much higher can you jump on the moon compared to the Earth?

    <p>6 times higher</p> Signup and view all the answers

    What is the SI unit of mass?

    <p>Kilogram</p> Signup and view all the answers

    What is the measure of inertia of an object?

    <p>Mass</p> Signup and view all the answers

    Which statement is true about the weight of an object?

    <p>It changes from place to place</p> Signup and view all the answers

    What does a weighing machine in a shop actually measure?

    <p>Mass</p> Signup and view all the answers

    What is the direction of the gravitational force between two objects?

    <p>Along the line intersecting both points</p> Signup and view all the answers

    What is the nature of the gravitational force compared to other fundamental forces?

    <p>It is a weak force, much weaker than electromagnetism and strong and weak nuclear forces</p> Signup and view all the answers

    What is the formula for the gravitational force between two objects?

    <p>F = G * (m1 * m2) / r^2</p> Signup and view all the answers

    What is the region around an object where the gravitational force can be detected?

    <p>Gravitational field</p> Signup and view all the answers

    What is the energy an object has due to its position within a gravitational field?

    <p>Potential energy</p> Signup and view all the answers

    What is the unit of the gravitational constant G?

    <p>N*m^2/kg^2</p> Signup and view all the answers

    Study Notes

    Kepler's Laws

    • Planetary motion follows three laws described by Johannes Kepler, known as Kepler's laws
    • Kepler's laws were derived from studying data on planetary positions and motion
    • Kepler's First Law: The orbit of a planet is an ellipse with the Sun at one of the foci
    • Kepler's Second Law: The line joining the planet and the Sun sweeps equal areas in equal intervals of time
    • Kepler's Third Law: The square of the period of revolution of a planet is directly proportional to the cube of the mean distance of the planet from the Sun

    Newton's Universal Law of Gravitation

    • Newton formulated his theory of Universal Gravity, which states that every object in the Universe attracts every other object with a definite force
    • The force is directly proportional to the product of the masses of the two objects and inversely proportional to the square of the distance between them
    • The gravitational force can be expressed mathematically as F = G * (m1 * m2) / d^2, where G is the Universal Gravitational constant

    Introduction to Scientists

    • Johannes Kepler (1571-1630) was a German astronomer and mathematician who discovered Kepler's laws
    • Sir Isaac Newton (1642-1727) was an English scientist who formulated Newton's laws of motion and the law of Universal Gravitation

    Force and Motion

    • A force is necessary to change the speed or direction of motion of an object
    • Newton's laws of motion and the law of Universal Gravitation help explain the behavior of objects on Earth and in the Universe

    Circular Motion and Centripetal Force

    • An object moving in a circle experiences a force directed towards the centre of the circle, known as the centripetal force
    • The centripetal force is necessary to keep the object moving in a circle and not flying off in a straight line
    • Examples of circular motion include the moon orbiting the Earth and the Earth orbiting the Sun

    Gravitation

    • Gravitation is a universal force that acts between all objects with mass
    • The force of gravitation is responsible for the motion of planets, stars, and galaxies
    • The force of gravitation is also responsible for the falling of objects on Earth

    Centripetal Force and Uniform Circular Motion

    • The centripetal force is related to the speed and radius of the circle by the equation F = m * v^2 / r
    • The force of gravitation provides the centripetal force necessary for uniform circular motion
    • The speed of an object in uniform circular motion can be expressed in terms of the period of revolution and the radius of the circle

    Solved Examples

    • Example 1: Calculating the gravitational force between two objects
    • Example 2: Calculating the velocity of an object in uniform circular motion### Mahendra's Acceleration
    • Mahendra's mass is 75 kg, and the force applied to him is 733 N.
    • Mahendra's acceleration is calculated as 9.77 m/s² using the formula a = F/m.
    • After 1 second, Mahendra's velocity is 9.77 m/s.

    Newton's Law of Gravitation

    • Every object attracts every other object with the same force.
    • The gravitational force due to the earth acts on the moon and artificial satellites, causing them to orbit the earth.

    Earth's Gravitational Acceleration

    • The earth exerts a gravitational force on objects near it, resulting in acceleration.
    • This acceleration is called acceleration due to gravity, denoted by 'g', and is directed towards the center of the earth.
    • The value of g on the surface of the earth is 9.77 m/s².

    Value of g on the Surface of the Earth

    • The value of g can be calculated using Newton's universal law of gravitation.
    • The formula for g is g = GM/r², where G is the gravitational constant, M is the mass of the earth, and r is the distance from the center of the earth.
    • The value of g on the surface of the earth is 9.77 m/s².

    Variation in Value of g

    • The value of g changes along the surface of the earth due to the earth's slightly ellipsoidal shape.
    • The value of g is highest at the poles (9.832 m/s²) and lowest at the equator (9.78 m/s²).
    • The value of g also changes with height, decreasing as the distance from the center of the earth increases.
    • The value of g changes if we go inside the earth, decreasing as the distance from the center of the earth decreases.

    Change of g with Height and Depth

    • The value of g decreases with increasing height, but the decrease is small for heights compared to the earth's radius.
    • The value of g also changes with depth, decreasing as we go deeper inside the earth.

    Mass and Weight

    • Mass is the amount of matter present in an object, measured in kilograms (kg).
    • Mass is a scalar quantity and does not change, even when going to another planet.
    • Weight is the force with which the earth attracts an object, measured in Newtons (N).
    • Weight is a vector quantity and changes from place to place, depending on the value of g.
    • Colloquially, weight is often used to refer to mass, but scientifically, weight refers to the gravitational force on an object.

    Universal Gravitation

    • Gravity is a universal force, acting between every point mass, attracting them to each other along the line intersecting both points.
    • This force is a two-way interaction, where both objects attract each other with the same force, but in opposite directions.
    • Compared to other fundamental forces, gravity is much weaker, but it can act over vast distances, even across millions of kilometers.

    Gravitational Forces

    • The gravitational force (F) between two objects is calculated by the equation: F = G * (m1 * m2) / r^2, where G is the gravitational constant (6.67408e-11 N*m^2/kg^2).
    • The masses of the two objects are represented by m1 and m2, and r is the distance between their centers.
    • A gravitational field is a region around an object where the gravitational force can be detected, and it is a vector field surrounding every object with mass.
    • Gravitational potential energy (U) is the energy an object has due to its position within a gravitational field, calculated by the equation: U = m * g * h.
    • The variables in this equation are the mass of the object (m), the acceleration due to gravity (g, approximately 9.8 m/s^2 on Earth), and the height of the object above the ground (h).

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    Description

    Learn about the three laws of planetary motion described by Johannes Kepler, including the shape of planetary orbits and their motion.

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