Properties Of Waves
Aim:
What are the properties of waves? Learning Questions: What are waves? What are the different types of waves? What is a medium? Can I explain the relationship between waves, matter and energy? Previous Tasks
None Next Task: 4. Play the "Making Waves Game" (Make sure you know how to read the properties of waves. Quiz on Friday.) |
Key Words
Wave transmit medium crest trough amplitude frequency compressional wave transversal wave |
BEFORE YOU BEGIN WATCH THIS VIDEO
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Introduction
Picture yourself sitting by the shore of a lake on a beautiful day. A fish jumps out of the water and falls back in, making a splash. You notice the circles of waves that move outward from the fish’s entry point. These outward circular waves pass by a duck and cause it to bob up and down. However, the duck did not move any closer to or any farther away from you. Why is that? If you notice the animation on the right has an object floating on a water wave. If you put your mouse over the object you will see that it may move up and down but it stays in the same place, just like the duck. This is because waves transmit energy but not matter. |
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Making Waves
If a pebble is thrown into water, you can see waves moving outward from where the pebble entered the water. Energy from the pebble’s splash causes the water to move up and down. The pebble caused a disturbance in the water. This disturbance caused a wave to move through the water in the form of up-and-down motion of water molecules. A wave is caused by a disturbance and transmits energy. The up-and-down movement of the water near the pebble was transferred to nearby water. In a wave, energy is transferred through vibrations, or back-and-forth movements. A vibrating particle transfers its energy to a nearby particle. This new particle then transfers the energy to yet another nearby particle, and so on. The material through which waves can travel is called a medium. A medium can be a gas, a liquid, or a solid. Waves that need a medium to travel are called mechanical waves. Water is the medium for objects and waves moving through the ocean. Air is the medium for the sound waves we hear at a band concert. An earthquake is another example of waves transferring energy. As the ground shakes up and down and from side to side, waves travel away from the source of the earthquake. The ground does not travel miles from the source; only the energy travels outward in a wave. |
Types of Waves
Transverse waves causes particles in matter to move back and forth at right angles to the direction in which the wave travels. If you tie a rope to a door handle and shake the end of the rope up and down, transverse waves travel through the rope. Compressional waves travel along a spring coil. This type of wave causes particles in matter to move back and forth along the same direction in which the wave travels. Where the coils are squeezed together are called compressions. The places where the coils are spread apart are called rarefactions. The series of compressions and rearefactions forms a compressional wave. Properties of Waves
To understand how waves behave, picture tying one end of rope to a doorknob and holding on the other end of the rope. If you flick the rope up, vertically, you have caused a disturbance. This starts a wave that moves along the rope away from the disturbance. The wave consists of a series of crests and troughs. The highest point on a wave is the crest, and the lowest point is called a trough. Waves can be described by several properties. The ones we will discuss are amplitude, wavelength and frequency. Amplitude is a measurement of how high the crest of wave rises or how low the measurement of how high the crest of a wave rises or how low the trough dips below the resting position. The larger the amplitude, the more energy is carried, resulting in a taller wave. Another property of a wave is wavelength. The distance between any two crests that are next to each other is the wavelength. Wavelengths can also be measured between two adjacent troughs
The number of waves produced in a given amount of times is the frequency. The word frequent means “often.” Frequency is measured by counting the number of crests or troughs that pass by a given point in one second. Think about snapping a rope back and fort to make a wave. The speed with which you snap the rope affects the frequency of the wave. The wave on the quickly snapped rope would have a higher frequency.
The amount of energy that is carried by a wave relates to the amplitude of a wave. A wave transporting HIGH energy has HIGH amplitude. A wave transporting LOW energy has LOW amplitude. Snapping the rope back and forth quickly requires more energy than snapping it slowly. If the amplitudes of two waves were equal, the quickly snapped rope would have more energy than the slowly snapped rope. The unit of measurement for frequency is hertz (Hz). For waves, one hertz equals one wave per second or 1Hz = 1/s. Frequency and wavelength are related. A wavelength with lower frequency has a longer wavelength. The opposite is also true. When frequency increases, more wave crests pass a fixed point each second and wavelength shortens. |
The figure below shows the "crest" and "trough" or the two parts of the wave. It also show amplitude, a wave property.
The figure below shows another property of a wave: wavelength.
The figure below shows the relationship between the frequency and the wavelength. As the frequency increases the wavelength decreases.
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Questions: Answer these questions on your worksheet.
1. Define wave:
2. What is a medium?
3. What is a mechanical wave?
4. What are three examples of mechanical waves given in this passage?
5. What are the two parts of a wave?
6. Define the properties of the waves and their relationship with energy.
Self Quiz
http://glencoe.mcgraw-hill.com/sites/0078617812/student_view0/unit4/chapter14/section_1_self-check_quiz-eng_.html
http://www.absorblearning.com/physics/demo/units/DJFPh064.html#Introduction
**What Is a Wave?
http://amazing-space.stsci.edu/resources/explorations/light/makewaves-frames.html
1. Define wave:
2. What is a medium?
3. What is a mechanical wave?
4. What are three examples of mechanical waves given in this passage?
5. What are the two parts of a wave?
6. Define the properties of the waves and their relationship with energy.
Self Quiz
http://glencoe.mcgraw-hill.com/sites/0078617812/student_view0/unit4/chapter14/section_1_self-check_quiz-eng_.html
http://www.absorblearning.com/physics/demo/units/DJFPh064.html#Introduction
**What Is a Wave?
http://amazing-space.stsci.edu/resources/explorations/light/makewaves-frames.html