WAVES: basics Chapters 25.1-25.8; 26

Simple Harmonic Motion The equal or balanced back and forth or side to side motion of a particle that is caused to vibrate by a disturbance. Similar to a pendulum’s motion. http://www.physics.uoguelph.ca/tutorials/shm/Q.shm.html

WHAT IS A WAVE? A repeating disturbance that causes vibrations and transmits energy through matter or space.

WHAT IS THE PURPOSE OF A WAVE? To transmit energy from one place to another.

WHAT HAPPENS TO ENERGY AS THE WAVE TRAVELS? Energy is transferred from one particle to the next. The motion of particles in a medium is like the motion of masses on a spring. Energy of the wave spreads away from the disturbance or vibration (see white board)

IS MATTER TRANSMITTED WITH THE WAVE? No, only energy is transmitted. The particles in the matter vibrate as the wave passes, but do not travel with the wave. http://www.infoline.ru/g23/5495/Physics/English/waves.htm http://members.aol.com/nicholashl/waves/movingwaves.html

ARE THERE DIFFERENT TYPES OF WAVES? Mechanical Waves Non-Mechanical Waves microwaves Sound waves

Mechanical Waves Waves that can only travel through matter Examples: sound, water and seismic waves In general, mechanical waves travel fastest through solids, then slower through liquids and slowest through gases Can be transverse or longitudinal (or compressional)

Non-Mechanical Waves Waves that can travel through matter or space (a vacuum) Example: electromagnetic radiation (waves) or light In general, non-mechanical waves travel fastest through a vacuum, then slower through gases, then liquids and slowest through solids Two perpendicular transverse waves

Electromagnetic Wave http://www.nrc-cnrc.gc.ca/obj/inms-ienm/images/research_images/optical_comb/COMBFIG1.gif

Wave Speed Wave speed (depends upon the composition and character of the medium it travels through)

Two types of waves based upon direction of vibrating particles: Transverse Waves cause particles in matter to vibrate perpendicular to the direction of wave travel. Longitudinal Waves cause particles in matter to vibrate in the same direction of wave travel. http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html

TRANSVERSE WAVE crest One wavelength amplitude Rest position trough

LONGITUDINAL WAVE Rarefaction (less dense) Compression (more dense) one wavelength

Wave Characteristics Frequency (f) (the number of vibrations that occur in a given time) Hertz (Hz) (# of vibrations per second) High frequency waves produce waves with short periods and short wavelengths Period (P) (the time it takes for one wave cycle to pass) Seconds (s) The lower the frequency, the longer the period

Wave Characteristics Wavelength λ (lambda) (the distance between one point on a wave to the next identical point; crest to crest, for example) Meters (m) The lower the frequency, the longer the wavelength Amplitude (longitudinal waves—the tightness of the compression; transverse waves—the distance from the crest to rest position or from trough to rest position) The greater the amplitude of the wave, the more energy the wave transfers.

Frequency vs. Intensity Rate of vibration (frequency) Amount of energy (intensity)— Amplitude (amount of displacement) loudness (relative intensity of sound) brightness (number of photons of light) Turn up the volume--same frequencies, different intensity

Why do waves become less intense away from the source? Same amount of energy is spread out over greater and greater distances. Same energy at every point along a wave front. Also, simple harmonic motion of the particles can be dampened (or absorbed or transferred) by the medium (rubber, clay, springs, fluids in shock absorbers)