Full Answer Section

Centripetal Force

• Definition: Centripetal force is a force that acts on an object moving in a circular path and is directed towards the center of that path.
• Key Points:
  • It is necessary to keep an object moving in a circle.
  • Examples: The force of gravity keeping the Moon in orbit around Earth, the tension in a string when you swing a ball on it.

Free Fall

• Definition: Free fall is the motion of an object falling under the sole influence of gravity.
• Key Points:
  • In the absence of air resistance, all objects in free fall accelerate towards the Earth at the same rate (approximately 9.8 meters per second squared).
  • This is why objects of different masses fall at the same rate in a vacuum.

Kepler’s Laws of Planetary Motion

1. Law of Orbits: All planets move in elliptical orbits with the Sun at one focus.
2. Law of Areas: A line segment joining a planet to the Sun sweeps out equal areas in equal intervals of time. This means that a planet moves faster when it is closer to the Sun and slower when it is farther away.
3. Law of Periods: The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit. This means that planets farther from the Sun take longer to orbit than those closer to the Sun.

Mass vs. Weight

• Mass:

  • A measure of the amount of matter in an object.
  • It is a scalar quantity (has magnitude but no direction).
  • It remains constant regardless of the object’s location.

• Weight:

  • The force of gravity acting on an object.
  • It is a vector quantity (has both magnitude and direction).
  • It varies depending on the gravitational field the object is in. For example, an object weighs less on the Moon than on Earth because the Moon’s gravity is weaker.

Why the Value of ‘g’ is Zero at the Center of the Earth

• ‘g’ (acceleration due to gravity): Represents the force of gravity per unit mass.
• At the Earth’s center:
  • The mass of the Earth is distributed symmetrically around you.
  • The gravitational forces from all directions cancel each other out.
  • Therefore, the net gravitational force and acceleration due to gravity (‘g’) become zero at the center of the Earth.