When analyzing motion from an accelerating reference frame, Newton's laws don't directly apply. We must add a pseudo (fictitious) force.

Pseudo Force: $F_{pseudo}$ = -m * $a_{frame}$

• Direction: opposite to the frame's acceleration
• Acts on every body in the non-inertial frame
• NOT a real force — no agent exerts it

Common Applications:

1. Accelerating vehicle: Pendulum tilts at angle theta = arctan$\frac{a}{g}$ opposite to acceleration. Effective gravity: $g_{eff}$ = sqrt($g^2$ + $a^2$).

2. Rotating frame: Centrifugal force = m*$omega^2$*r (outward) and Coriolis force = -2m(omega x v) appear as pseudo forces.

3. Elevator: The apparent weight change is naturally handled by pseudo force: In elevator frame, pseudo force = -$ma_{elevator}$ acts on person.

When to Use:

• Ground frame: No pseudo force needed. Most JEE problems are solved here.
• Non-inertial frame: Add pseudo force. Sometimes simpler for specific problems (e.g., block on an accelerating wedge analyzed from the wedge frame).