P1.5 WAVES 3

P1.5 WAVES 3

1. SOUND

   • caused by vibration in a medium, which are detected as a sound
     • these Mechanical Vibrations are passed through the surrounding medium as a series of compressions
   • type of LONGITUDINAL Wave
   • eventually sound will reach person's eardrum so person may hear it
   • travels faster in: solids, then liquids, then gases
   • cannot travel in space as no particles (almost a vaccumm)
   • can be reflected by hard, flat surfaces
     • things (furniture) absorb the sounds quickly & stop it echoing around the room
     • ECHOES- Reflected sound waves
     • Hear a delay between original sound & echo because the echoes sound waves have to travel further so takes longer to reach ears
     • Sound waves also refract (change direction) as they enter different media. As enter denser material, speed up
       • since sound waves spread out so much, change in direction is difficult to identify in normal circumstances
   • Higher frequency= high pitched (squeaking mouse)
     • Low frequency= low pitched (mooing cow)
       • Bigger amplitude= louder sound

2. DOPPLER EFFECT

   • sound waves from stationary object are equally spaced
   • Happens to both longitudinal & transverse waves
     • wave source could be light, sound or microwaves
   • If a wave source is moving relative to an observer, there will be a change in the observed wavelength and frequency
   • source moves AWAY from observer, observed wavelength increases & frequency decreases
   • source moves TOWARDS observer, observed wavelength decreases & frequency increases

3. RED SHIFT

   • There is an observed increase in wavelength of light from most distant galaxies. Further away galaxies are= faster they are moving & bigger the observed increase in wavelength (effect is called red-shift).
   • Further away galaxy= greater red shift
     • shows more distant galaxies are moving away faster
       • provides evidence that universe seems to be expanding

4. BIG BANG

   • WHAT? universe began from a very small initial point, a singularity
   • can use the current rate of expansion of the universe to estimate that the BB happened 14 billion years ago
   • STEADY STATE THEORY says universe has always existed as it is now & always will do
   • BB theory is theory that can explain the existence of CMBR (Cosmic Microwave Background Radiation)
   • CMBR is form of electromagnetic radiation filling the universe. Comes from radiation that was present shortly after beginning of universe
   • LIMITATIONS
     • some astronomers believe in SST, others dont want to change mind
     • Observations that the theory cant explain yet, like BB theory predicts universe's expansion should be slowing down but actually speeding up
     • doesnt explain what caused the explosion Or conditions b4 explosion
   • EVIDENCE
     • from observed red shift from other galaxies, see universe is expanding. So some point in past everything must have started expanding from same point
     • CMBR- form of radiation present everywhere in universe. BB theory only theory that can explain this