Why does a solid have a definite shape? the particles of a solid vibrate in fixed positions. the particles of a solid have no forces of attraction between them. the particles of a solid cannot change shape. the particles of a solid cannot move at all.

It may seem strange that the selected velocity does not depend on either the mass or the charge of the particle. (for example, would the velocity of a neutral particle be selected by passage through this device? ) the explanation of this is that the mass and the charge control the resolution of the device--particles with the wrong velocity will be accelerated away from the straight line and will not pass through the exit slit. if the acceleration depends strongly on the velocity, then particles with just slightly wrong velocities will feel a substantial transverse acceleration and will not exit the selector. because the acc