Physical Science / Unit 9: Waves, Sound and Light
9.1 What Are Waves?
Notes
A wave is a disturbance that transfers energy from place to place without transferring matter.
- Mechanical waves need a medium (water, air, rope). Electromagnetic waves can travel through empty space.
- Transverse waves: particles move perpendicular to the direction of the wave (light, rope wave). Longitudinal waves: particles move parallel to the wave direction (sound, with compressions and rarefactions).
- Parts of a transverse wave: crest (top), trough (bottom), amplitude (height from rest position), wavelength (distance between two crests).
Practice
Waves transfer:
Waves move energy without moving the medium along with them.
Which wave does NOT need a medium?
Electromagnetic waves travel through a vacuum.
In a longitudinal wave, the particles of the medium move:
Sound is a longitudinal wave of compressions and rarefactions.
Ready for more? Take the Unit 9 test.