In a transverse wave the particles of the medium vibrate perpendicular to the direction of wave propagation (example: a wave on a stretched string, light waves). In a longitudinal wave the particles vibrate parallel to the direction of propagation, forming compressions and rarefactions (example: sound waves in air).

v = f * lambda

Newton's second law: the rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the force. F = dp/dt = d(mv)/dt. For constant mass, F = m (dv/dt) = m a.

F = dp/dt = m a

Systematic errors have a definite cause and always shift readings in one direction (e.g. a zero error in an instrument, or a mis-calibrated scale); they can be minimised by correcting the instrument. Random errors occur due to unpredictable fluctuations and vary in size and sign; they are reduced by taking many readings and averaging.