Key Concepts: Non-Inertial Frames & Pseudo-Forces

Non-Inertial Reference Frames

• A non-inertial frame is one that is accelerating. Newton's laws don't directly apply without modifications.
• To use F = ma in a non-inertial frame, we introduce pseudo-forces (fictitious forces).

Common Pseudo-Forces

• Pseudo-force in a linearly accelerating frame: F_pseudo = −ma_frame. You feel pushed backward when a car accelerates forward.
• Centrifugal force: An outward pseudo-force felt in a rotating frame. F = mω²r (outward). It's not a real force — it's the result of inertia in a rotating reference frame.
• Coriolis force: Affects moving objects in a rotating frame. It deflects winds on Earth (right in the Northern Hemisphere, left in the Southern).

Key Point

• Pseudo-forces are mathematical tools — they have no real physical source (no action-reaction pair).
• In an inertial frame, the same phenomena are explained by the absence of centripetal force, not by centrifugal force.