Waves Sound Waves Objectives 1. Recognize that waves transfer energy. 2. Distinguish between mechanical waves and electromagnetic waves. 3. Explain the relationship between particle vibration and wave motion. 4. Distinguish between transverse waves and longitudinal waves. Demonstration: Harmonic Motion, ATE p. 358. This will demonstrate the harmonic motion of a mass on a spring.  

What Is a Wave? A disturbance Transmits energy not matter Through matter and space Medium-matter through which a wave travels Sound waves require a medium

Waves Transfer Energy Eye, photo film Waves can do work Examples Sand Eardrum Eye, photo film

Sound When sound travels in the air, the waves spread out as spheres As they travel outward they get bigger

Longitudinal Wave Types of Wave Motion Waves, such as water or sound waves, are a periodic disturbance of the medium through which they travel. For longitudinal waves, the medium is displaced in the direction of travel. For example, air is compressed and expanded (figure 1) in the same direction that a sound wave travels. Earthquakes generate both P (compression, or longitudinal) and S (shear, or transverse) waves, which travel at different speeds and follow different paths. These differences allow seismologists to estimate where the earthquake occurred. Atomic particles and light can be described by probability waves that, while fundamentally different, behave much like the ripples on a pond.

Vibrations of the drum head create sound waves in the air

Sound Waves Are Pressure Waves Pressure nodes appear symmetrically at each end Open to the atmosphere Sound waves are pressure waves so pressure nodes appear symmetrically at each end where they open to the atmosphere.

Standing Wave Fundamental frequency for each pipe Wavelength =  = 2L Frequency = f = v / 2L Shorter the length higher the frequency

Harmonics  = L f = v / L Even numbered multiples of the fundamental

Pitch Large wavelength -> Low frequency -> Low pitch Small wavelength -> High frequency -> High pitch

Moving Sound Source As the source of a wave moves The wave fonts bunch up in front Spread out behind www.physics.mun.ca/~jjerrett/ doppler/doppler.html The truck is producing sound waves (circles) as it moves. Each successive wave is produced at a different position. Once a wave is produced it spreads out in a circle from that position at the speed of sound and the motion of the truck has no further effect on it. Since the sound waves travel at a constant speed, the motion of the truck causes the waves infront of the truck to be closer together (shorter wavelength, higher frequency) and those waves behind the truck to be further apart (longer wavelength, lower frequency).

The Doppler Effect

What if the disturbance is traveling at the same speed as the wave fronts?

What if the disturbance is traveling faster than speed of the wave fronts?

Bow Wave

Bow Wow Waves Bow Waves Demonstrate on the overhead with wide shallow glass of water

Through the viewfinder of his camera, Ensign John Gay could see the fighter plane drop from the sky heading toward the port side of the aircraft carrier Constellation.  At 1,000 feet, the pilot drops the F/A-18C Hornet to increase his speed to 750 mph,  vapor flickering off the curved surfaces of the plane. In the precise moment a cloud in the shape of a farm-fresh egg forms around the Hornet 200 yards from the carrier, its engines rippling the Pacific Ocean just 75 feet below, Gay hears an explosion and snaps his camera shutter once.  "I clicked the same time I heard the boom, and I knew I had it,"  Gay said. What he had was a technically meticulous depiction of the sound barrier being broken July 7, 1999, somewhere on the Pacific between Hawaii and Japan. Sports Illustrated, Brills Content and Life ran the photo. The photo recently took first prize in the science and technology division in the World Press Photo 2000 contest, which drew more than 42,000 entries worldwide.  "All of a sudden, in the last few days, I've been getting calls from everywhere about it again.  It's kind of neat," he said, in a telephone interview from his station in Virginia Beach, Va.  A naval veteran of 12 years, Gay, 38, manages a crew of eight assigned to take intelligence photographs from the high-tech belly of an F-14 Tomcat, the fastest fighter in the U.S. Navy. In July, Gay had been part of a Joint Task Force Exercise as the Constellation made its way to Japan. Gay selected his Nikon 90 S, one of the five 35 mm cameras he owns.  He set his 80-300 mm zoom lens on 300 mm, set his shutter speed at 1/1000 of a second with an aperture setting f F5.6.  "I put it on full manual, focus and exposure," Gay said.  "I tell  young photographers who are into automatic everything,  you aren't going to get that shot on auto. The plane is too fast. The camera can't keep up." At sea level a plane must exceed 741 mph to break the sound barrier, or the speed at which sound travels.  The change in pressure as the plane outruns all of the pressure and sound waves in front of it is heard on the ground as an explosion or sonic boom. The pressure change condenses the water in the air as the jet passes these waves. Altitude, wind speed, humidity, the shape and trajectory of the plane - all of these affect the breaking of this barrier. The slightest drag or atmospheric pull on the plane shatters the vapor oval like fireworks as the plane passes through, he said everything on July 7 was perfect, he said. "You see this vapor flicker around the plane that gets bigger and bigger. You get this loud boom, and it's instantaneous. The vapor cloud is there, and then it's not there. It's the coolest thing you have ever seen."

What happens when a flying witch breaks the sound barrier?   You hear the broom boom!

                                                                                Sound is made up of molecules of air that move. They push together and gather together to form sound waves . Sound waves travel at the speed of about 750 mph at sea level. When a plane travels the speed of sound the air waves gather together and compress the air in front of the plane to keep it from moving forward. This compression causes a shock wave to form in front of the plane. In order to travel faster than the speed of sound the plane needs to be able to break through the shock wave. When the airplane moves through the waves, it is makes the sound waves spread out and this creates a loud noise or sonic boom . The sonic boom is caused by a sudden change in the air pressure. When the plane travels faster than sound it is traveling at supersonic speed. A plane traveling at the speed of sound is traveling at Mach 1 or about 760 MPH. Mach 2 is twice the speed of sound.

Period Time required for a full wavelength to pass Symbol is T SI unit is seconds

Frequency Frequency measures the rate of vibrations

Frequency Number of vibrations that occur in an 1 sec time interval Period – the time required for one full wavelength to pass a certain point