Elliptical Orbits - Cambridge (CIE) IGCSE Physics

Overview

• Elliptical Orbits: The orbits of planets, minor planets, and comets are elliptical.
  • An ellipse is a "squashed" circle.
  • Planets and Minor Planets: Slightly elliptical, often considered circular with the Sun at the center.
  • Comets: Highly elliptical, with the Sun at one of the two foci of the ellipse.

Elliptical Orbit of a Planet

• Planets, minor planets, and comets travel in elliptical orbits where the Sun is not at the center.

Comet Speed

• Variable Speed: An object's speed in an elliptical orbit varies with its distance from the Sun.
  • Stable Orbits: Despite the non-circular path, these orbits remain stable.
  • Radius and Speed: In a stable orbit, the radius must change if the orbital speed changes.

As the Comet Approaches the Sun:

• The radius decreases.
• The orbital speed increases due to the Sun's gravitational pull.

As the Comet Moves Away from the Sun:

• The radius increases.
• The orbital speed decreases due to a weaker gravitational pull.

Conservation of Energy in Elliptical Orbits

• Energy Conservation: Energy is conserved as gravitational potential energy converts to kinetic energy and vice versa.

As the Comet Approaches the Sun:

• Loses gravitational potential energy.
• Gains kinetic energy, causing it to speed up.

As the Comet Moves Away from the Sun:

• Gains gravitational potential energy.
• Loses kinetic energy, causing it to slow down.

Examiner Tips and Tricks

• Calculations involving elliptical orbits are generally not required; assume circular if calculations are needed.
• Kinetic energy is defined by ( \frac{1}{2}mv^2 ), where ( m ) is mass and ( v ) is velocity.
• If an object's speed increases, its kinetic energy increases, and gravitational potential energy decreases to conserve energy.

Summary

• The lecture provided an understanding of elliptical orbits, focusing on the paths of planets and comets, how speed varies with distance from the Sun, and the conservation of energy in elliptical orbits.

Last Updated: 1 October 2024.