Waves and vibrations

• Mechanical waves are waves that pass through a substance.
• EM waves (electromagnetic waves) are caused by the oscillating electric and magnetic fields that progress through space without the need for a substance (they can travel through a vaccum). EM waves are transverse, as their oscillations occur at right angles to one another.
• Longitudinal waves are waves in which the direction of vibrations of particles is parallel to the direction that the wave is travelling (e.g. sound waves, P-waves, compression waves on a slinky).

  A longitudinal wave has rarefractions and compressions.
• Transverse waves are waves in which the directin of the vibration of the particles is perpendicular to the direction in which the wave travels. (e.g. EM waves, S-waves)

  
• Transverse waves are plane-polarised if the vibrations stay in one plane only. If the vibrations change from one plane to another, the waves are unpolarised.

  *Longitudinal waves cannot be polarised.
• Polaroid sunglasses reduce the glare of light that is reflected by water or glass. This reflected light is polarised and the intensity is reduced when it passes through the sunglasses. This is helpful as it protects their eyes from UV light.