Newton's Third Law of Motion: Application in Jet and Rocket Engines

Introduction

• Newton's Third Law: For every action, there is an equal and opposite reaction.

Jet Engines

• Structure:
  • Tube, open at one end, closed at the other.
  • Fuel piped in and set on fire, producing hot gas.
• Process:
  • Gas generated inside expands, shoots out the open end.
  • Gas has mass and velocity, thus momentum (action).
  • Reaction: Body of engine and attached airplane move in the opposite direction.
  • Misconception: Gas pushing on air is not the main mechanism.

Rocket Engines

• Similar to jet engines but also carries oxygen.
• Reason for carrying oxygen:
  • Rockets go into space where there's no air.
• Action-Reaction:
  • Huge mass of gas expelled with enormous velocity.
  • Rocket moves in opposite direction.

Design and Optimization

• Jet Engine Efficiency:
  • Increase velocity (v) of escaping gas by narrowing the tube's end.
  • Increase mass (m) by burning more fuel.
• Rocket Engine Challenges:
  • Increasing fuel increases overall mass.
  • Diminishing returns: Rockets become larger without proportional increase in speed.

Practical Examples

• Saturn V Rocket:
  • Massive rockets required to reach the moon.
• Space Shuttle:
  • Large fuel tanks and boosters used for takeoff.
• Challenges in Space Travel:
  • Long travel times to Mars (6 months) pose social challenges for astronauts.

Ion Engines

• Ionization Process:
  • Atom gains/loses electrons, becomes charged.
  • Charged ions moved by electric fields.
• Structure and Function:
  • Long tube with electric coils generates field.
  • Ions accelerated and expelled at high velocity.
  • Provides steady, gentle acceleration over time.
• Comparison to Chemical Rockets:
  • Ion engines lack thrust to counteract gravity for launch.
  • Used in space for continuous acceleration.
• Optimizing Ion Engines:
  • Use heavy gases like xenon for ions.

Conclusion

• Application of Newton's Third Law in propulsion technologies.
• Ion engines offer potential for faster space travel with small amounts of material and high velocities.

This lecture highlights how Newton's Third Law is a fundamental principle in the design and operation of both jet and rocket engines, and its innovative applications in ion engines for space travel.