4 What are mechanical waves? What do you think waves carry? Can you see waves? Examples?
5 Mechanical WavesMechanical waves are disturbances in matter that carry energy from one place to another.Usually require matter through which to travelThe matter a wave travels through is called a medium.Medium can be a solid, liquid, or gasSome waves can travel through space…with no medium!
17 Period vs FrequencyPeriod – (T) – The time it takes for one cycle (= how long?)Measured in secondsFrequency – (f) – The number of cycles in a given time (= how many?)Measured in Hertz (Hz)
18 Speed of a wave We find speed by distance divided by time. The same holds true for waves!Speed of a wave = Wavelength/PeriodSpeed of a wave = Wavelength*Frequency
19 Speed of a Wave The speed of a wave is constant within a medium. The speed can change when a wave enters a new mediumAll waves of the same type travel at the same speedThis means wavelength is inversely proportional to frequency!If the wavelength increases the frequency has to decrease!If the wavelength decreases the frequency has to increase!
26 LoudnessSubjective! (This means it depends on the person who is hearing it.)Loudness is a personal, physical response to the intensity of sound.As intensity increases, so does loudness, but loudness also depends on the listener’s ears and brain.
27 Ultrasound Most people hear sounds between 20 and 20,000 Hz. Infrasound – sound at frequencies lower than people usually hearUltrasound – sound at frequencies higher than people usually hearUsed in technologies such as sonar and ultrasound imaging
28 Ultrasound, ctd.Sonar – a technique used to determine the distance to an object under water.Ultrasound – medical technique used to take pictures of different organs (or a fetus!)
29 Hearing & the Ear Ear consists of 3 main parts Outer Ear – gathers and focuses soundMiddle Ear – receives and amplifies vibrationsInner Ear – uses nerve endings to sense vibrations and send signals to the brain
32 What happens when… A wave meets a hard surface like a wall? A wave enters a new medium?A wave moves around an obstacle?A wave meets another wave?
33 A wave meets a hard surface like a wall? ReflectionA wave bounces off a surface that it can not pass throughReflection does not change the speed or frequency of the wave, BUT the wave can be flipped upside down!