Space Physics Lecture Notes - Flashcards

This course explores fundamental questions about space, focusing on how objects move and interact within it. Key topics include:

Travel to Proxima Centauri (4.3 light-years away) would take approximately 43{,}000 ext{ years} even at a speed of 30 ext{ km/s}. This highlights the vast distances and long travel times in space.
Communication delays (e.g., between Earth and Mars) are governed by the speed of light, resulting in significant light-time delays (minutes).

Newton's Laws of Motion are central:
- Law 1 (Inertia): Objects maintain constant velocity unless an external force acts (p = mv).
- Law 2 (Force and Momentum): Net force equals the rate of change of momentum (F ext{_net} = dp/dt; F=ma for constant mass).
- Law 3 (Action-Reaction): Every force has an equal and opposite reaction force.
Conservation of Momentum: Total momentum is conserved in interactions. This is the core principle behind rocket propulsion. Rockets work by ejecting mass (propellant) backward at high speed, causing the remaining rocket mass to accelerate forward. Constant thrust on a decreasing mass leads to increasing acceleration.
Propulsion types include chemical, high-pressure gas, ionic, and light sails (which use photon momentum).
Gravity slingshots (gravitational assists) utilize a planet's gravity to change a spacecraft's velocity and direction without expending propellant.

Vacuum is the absence of matter and pressure; it does not actively 'pull'. Instead, pressure differences drive forces from higher-pressure regions to lower-pressure regions.
Gas pressure is caused by gas particles colliding with surfaces (P = F/A).
In space, swooping and gliding are impossible in a vacuum because there is no air to push against; propulsion requires ejecting mass.
Pressure management is critical for space infrastructure like the ISS.

In a true vacuum, sound cannot travel because there is no medium for pressure waves to propagate.
While traditional 'sound' is absent, some regions of space with very sparse gas (interstellar medium) can carry long-wavelength pressure waves detectable by specialized instruments (e.g., Chandra X-ray Observatory detections in galaxy clusters).