What governs the curvature and fluidity of membrane.

The shapes of different lipids influence how much a membrane can curve (i.e. bend). The intrinsic molecular volume of the head-group and composition of the fatty acyl chains (i.e. saturated vs unsaturated) in lipids will determine strict steric dimensions and distinct shapes for each lipid species.

Explanation:

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me