Wave Period Amplitude Crest Trough Frequency Hertz Wavelength Please use your own sheet of paper to define the following vocabulary terms: Wave Period Amplitude   Crest  Trough Frequency Hertz Wavelength Transverse wave Longitudinal wave

Mechanical Waves

What are mechanical waves? What do you think waves carry? Can you see waves? Examples?

Mechanical Waves Mechanical waves are disturbances in matter that carry energy from one place to another. Usually require matter through which to travel The matter a wave travels through is called a medium. Medium can be a solid, liquid, or gas Some waves can travel through space…with no medium!

How are mechanical waves created?

Creation of mechanical waves: Need a source of energy! That energy causes a vibration to travel through the medium

Types of Mechanical Waves Transverse: A wave that causes the medium to vibrate at right angles to the direction of the wave

Parts of a transverse wave:

Types of Mechanical Waves, ctd. Longitudinal: A wave in which the vibration of the medium is parallel to the direction the wave travels

Parts of a longitudinal wave:

Remember! A wave doesn’t move the medium…it’s just energy traveling through the medium!

Transverse and Longitudinal Wave Which is which?

Measuring Wave Movement Period vs. Frequency

What is Frequency Frequency – (f) – The number of cycles in a given time Or the number of waves that pass a certain point in a given time (usually a second). Measured in Hertz (Hz) 1 Hz = 1 wave (cycle) per second 1 wave/1 s

Calculating Frequency To find frequency: Divide the number of waves observed by the amount of time you spend observing them. f = wave (cycles) time So if you observe 10 waves in 5 seconds, what is the frequency of the waves?

What is the relationship between wavelength and frequency? Wavelength is inversely proportional to frequency! If the wavelength increases the frequency has to decrease! Why is this so? If wavelength increases, it takes longer for the waves to pass through the medium which lowers the number of waves you will see in any amount of time If the wavelength decreases the frequency has to increase!

What is the period of a wave? The time it takes for one wave (cycle) to occur. Represented by T Measured by timing how long it takes for a complete wave to pass a given point. Measured in seconds

Comparing frequency & period Frequency is the inverse of the Period f = 1 / T And so…. Period is the inverse of the frequency T = 1/f WHAT DOES THAT MEAN? E.g. If Wave A has a frequency of 4waves/s, it’s period will be 1/4s

Speed of a wave We find speed by calculating distance divided by time. The same holds true for waves! Speed of a wave = Wavelength x Frequency V = λ f Since this is a speed or velocity, the units of measure will be m/s.

Practice Problem #1: v = λ f v = 10 m * 50 Hz v = 500 m/s A wave has a frequency of 50 Hz and a wavelength of 10m. What is the speed of the wave? v = λ f v = 10 m * 50 Hz v = 500 m/s

Practice Problem #2: f = v / λ f = 5 m/s / 2 m f = 2.5 Hz The speed of a wave is 5 m/s . Its wavelength is 2m. What is the frequency of the wave? f = v / λ f = 5 m/s / 2 m f = 2.5 Hz

Practice Problem #3: Find the wavelength of a wave in a rope that has a frequency of 2.0 Hz and a speed of 0.4 meters/second. λ = v / f λ = 0.4 m/s / 2.0 Hz λ = 0.2 m

Practice Problem #4: The wavelength of a wave is 20 m. Its speed is 100 m/s. Calculate the frequency of the wave. f = v / λ f = 100 m/s / 20 m f = 5 Hz Calculate the period of the same wave. T = 1 / f T = 1/5 Hz T = 0.2 s