*Vibration - either sinusoidal vibration or gyratory vibration.
**Sinusoidal Vibration occurs at an angled plane relative to the horizontal.  The vibration is in a wave pattern determined by frequency and amplitude.
**Gyratory Vibration occurs at near level plane at low angles in a reciprocating side to side motion.
*Gravity - This physical interaction is after material is thrown from the screen causing it to fall to a lower level.  Gravity also pulls the particles through the screen media.
*Density - The density of the material relates to material stratification.
*Electrostatic Force -  This force applies to screening when particles are extremely dry or is wet.