Mechanical & Nonmechanical Waves Mechanical waves require a material medium. Examples are: Sound waves Water waves Shock waves in an explosion Other waves, such as electromagnetic waves, do not require a material medium. Examples are: Light X-rays Radio waves
Pulse Waves and Periodic Waves Pulse wave- a wave which consists of a single, non-repeated disturbance or pulse. Animation courtesy of Dr. Dan Russell, Kettering University
Pulse Waves and Periodic Waves Periodic wave- a wave whose source is some form of periodic motion. Animation courtesy of Dr. Dan Russell, Kettering University
Sinusoidal Waves A periodic wave whose source vibrates with simple harmonic motion produces a sinusoidal wave. This is a wave whose graph is shaped like a sine or cosine graph.
Quick-lab 1: Types of Waves Using the thin coiled spring, send a single pulse down the spring as demonstrated by your instructor. In which direction was the wave energy moving? In which direction(s) did the spring move? Using the slinky spring, send a single pulse down the spring, as demonstrated by your instructor. In which direction was the wave energy moving? In which direction did the spring move?
Transverse and Longitudinal Waves Transverse wave – a wave whose particles vibrate perpendicular to the direction of travel of the wave. Examples include: Surface waves on water. Electromagnetic waves Animation courtesy of Dr. Dan Russell, Kettering University
Transverse and Longitudinal Waves Longitudinal wave- a wave whose particles vibrate parallel to the direction of travel of the wave. Examples include: Sound waves Compression waves in explosions. Animation courtesy of Dr. Dan Russell, Kettering University
Frequency and Period Frequency – the number of crests (or troughs) passing a reference point per second. Frequency Frequency is measure in cycles/second 1 Cycle/second = 1 s -1 = 1 Hertz Period – the time between the passage of two successive wave crests (or troughs) past a reference point. The period is a time interval, so it is measured in seconds. The frequency is the reciprocal of the period. We also say frequency and period are inversely related.
Quick Lab 2: Wave Speed Using the coiled spring to send transverse pulse waves. Using the stopwatch, time how long it takes for the pulse to travel the length of the spring. Try timing the speed of pulses with different amplitudes.
Wave Speed Wave speed: The speed of the moving disturbance. v = f
Quick Lab 3: Wave Equation Using the coiled spring to make transverse waves. Change the frequency of the waves and observe what happens to the wavelength.
Wave Speed Practice Problem A tuning fork produces a sound with a frequency of 256 Hz and a wavelength in air of 1.35 meters. What is the speed of sound in air? Answer: v = 346 m/s
Power and damping power- the rate of transfer of energy by a wave. The power of a wave is proportional to the square of the wave amplitude and also to the square of the wave frequency damping – the reduction in amplitude of a wave due to the dissipation of wave energy as it travels away from the source.
Quick Lab 4: Wave Interactions Using the Slinky ® or the thin coil spring, have students on both end of the spring launch pulses as the same time. Experiment with what happens when two pulses meet in the middle of the spring.
Superposition superposition – the combination of two overlapping waves. When waves overlap, the displacements of the waves at each point are added to find the resultant displacement. Animation courtesy of Dr. Dan Russell, Kettering University
Constructive Interference constructive interference – when individual displacements on the same side of the equilibrium position are added together to form the resultant wave. The resultant displacement is larger than either of the component displacements.
Destructive Interference destructive interference – when individual displacements on opposite sides of the equilibrium position are added together to form the resultant wave. The resultant is smaller than at least one of the component displacements.
Quick Lab 5: Standing waves As demonstrated by your instructor, shake the spring with a gradually increasing frequency, and observe what happens at certain fast enough frequencies.
Standing Waves standing wave – a wave pattern that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere. Animation courtesy of Dr. Dan Russell, Kettering University
Standing Waves node – a point in a standing wave that always undergoes complete destructive interference and therefore is stationary. antinode – a point in a standing wave, halfway between two nodes, at which the largest amplitude occurs.