CK12 Unit 5 part 1 (mechanical, transverse, longitudital, and surface waves)

assignments - 100% on practice - mechanical waves

                           100% on practice - transverse waves

                           100% on practice - longituditional waves

                           100% on practice - surface waves

If not using a computer - must answer review questions (must write questions too)/files/user/923/file/Unit%205%20P%201%20%20Mechanical%2C%20transverse%2C%20longitudinal%2C%20surface%20Wave.docx

Mechanical Wave

Introduces waves in matter and how they transfer energy.

·        Describe mechanical waves.

·        Define the medium of a mechanical wave.

·        Identify three types of mechanical waves.

No doubt you’ve seen this happen. Droplets of water fall into a body of water, and concentric circles spread out through the water around the droplets. The concentric circles are waves moving through the water.

Waves in Matter

The waves in the picture above are examples of mechanical waves. A mechanical wave is a disturbance in matter that transfers energy through the matter. A mechanical wave starts when matter is disturbed. A source of energy is needed to disturb matter and start a mechanical wave.

Q: Where does the energy come from in the water wave pictured above?

A: The energy comes from the falling droplets of water, which have kinetic energy because of their motion.

The Medium

The energy of a mechanical wave can travel only through matter. The matter through which the wave travels is called the medium (plural, media). The medium in the water wave pictured above is water, a liquid. But the medium of a mechanical wave can be any state of matter, even a solid.

Q: How do the particles of the medium move when a wave passes through them?

A: The particles of the medium just vibrate in place. As they vibrate, they pass the energy of the disturbance to the particles next to them, which pass the energy to the particles next to them, and so on. Particles of the medium don’t actually travel along with the wave. Only the energy of the wave travels through the medium.

Types of Mechanical Waves

There are three types of mechanical waves: transverse, longitudinal, and surface waves. They differ in how particles of the medium move. You can see this in the Figure belowand in the animation at the following URL.http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html

·        In a transverse wave, particles of the medium vibrate up and down perpendicular to the direction of the wave.

·        In a longitudinal wave, particles of the medium vibrate back and forth parallel to the direction of the wave.

·        In a surface wave, particles of the medium vibrate both up and down and back and forth, so they end up moving in a circle.

Q: How do you think surface waves are related to transverse and longitudinal waves?

A: A surface wave is combination of a transverse wave and a longitudinal wave.

Summary

·        A mechanical wave is a disturbance in matter that transfers energy through the matter.

·        The matter through which a mechanical wave travels is called the medium (plural, media).

·        There are three types of mechanical waves: transverse, longitudinal, and surface waves. They differ in how particles of the medium move when the energy of the wave passes through.

Explore More

At the following URL, read the short introduction to waves and watch the animations. Then answer the questions below. http://www.acs.psu.edu/drussell/Demos/waves-intro/waves-intro.html

1.      The article gives a dictionary definition of wave. What is the most important part of this definition?

2.      What happens to particles of the medium when a wave passes?

3.      How is “doing the wave” in a football stadium like a mechanical wave?

Review

1.      Define mechanical wave.

2.      What is the medium of a mechanical wave?

3.      List three types of mechanical waves.

4.      If you shake one end of a rope up and down, a wave passes through the rope. Which type of wave is it?

Transverse Wave

Waves in the ocean are one kind of transverse wave.

·        Describe transverse waves.

·        Identify the crests and troughs of a transverse wave.

·        Define S waves.

Can you guess what this picture shows? Here’s a hint: the objects in the picture have been magnified, and one of them is moving rapidly. The objects are guitar strings, and the moving string is the one on the bottom right. The string is moving because it has just been plucked. Plucking the string gave it energy, which is moving through the string in amechanical wave. A mechanical wave is a wave that travels through matter. The matter a mechanical wave travels through is called the medium. The type of mechanical wave passing through the vibrating guitar string is a transverse wave.

What Is a Transverse Wave?

A transverse wave is a wave in which particles of the medium vibrate at right angles, or perpendicular, to the direction that the wave travels. Another example of a transverse wave is the wave that passes through a rope with you shake one end of the rope up and down, as in the Figure below. The direction of the wave is down the length of the rope away from the hand. The rope itself moves up and down as the wave passes through it. You can watch a video of a transverse wave in a rope at this URL:http://www.youtube.com/watch?v=TZIr9mpERbU.

To see a transverse wave in slow motion, go to this URL: http://www.youtube.com/watch?v=g49mahYeNgc.

Q: When a guitar string is plucked, in what direction does the wave travel? In what directions does the string vibrate?

A: The wave travels down the string to the end. The string vibrates up and down at right angles to the direction of the wave.

Crests and Troughs

A transverse wave is characterized by the high and low points reached by particles of the medium as the wave passes through. The high points are called crests, and the low points are called troughs. You can see both in the Figure below.

S Waves

Transverse waves called S waves occur during earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions away from the disturbance. S waves may travel for hundreds of miles. An S wave is modeled in the Figure below.

Summary

·        A transverse wave is a wave in which particles of the medium vibrate perpendicular to the direction that the wave travels.

·        The high points of a transverse wave are called crests, and the low points are called troughs.

·        S waves are transverse waves that travel through underground rocks during earthquakes.

Explore More

At the following URL, review transverse waves and watch the animations. Be sure to view the slow motion video of a transverse wave moving through a bungee cord. Then answer the questions below.http://www.acoustics.salford.ac.uk/feschools/waves/wavetypes.htm#trans

1.      Give two examples of transverse waves.

2.      How can you make a transverse wave in a Slinky spring toy?

3.      Based on the animation in the article, draw a sketch to show what happens to particles of the medium in a transverse wave. Include arrows to show the direction the particles move and the direction the wave travels.

Review

1.      What is a transverse wave?

2.      Sketch a transverse wave and label the crests and troughs.

3.      Infer how S waves might affect structures such as buildings.

Longitudinal Wave

Waves oscillating in the same direction they are traveling.

·        Describe a longitudinal wave.

·        Identify compressions and rarefactions of a longitudinal wave.

·        Define P waves.

You’ve probably played with Slinky spring toys like these. They’re simple toys, but they can move in very interesting ways. Pushing in on the end of a spring toy, for example, gives it energy that moves through the spring in a longitudinal wave.

What Is a Longitudinal Wave?

A longitudinal wave is a type of mechanical wave. A mechanical wave is a wave that travels through matter, called the medium. In a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction that the wave travels. You can see this in the Figure below. The person’s hand pushes and pulls on one end of the spring. Theenergy of this disturbance passes through the coils of the spring to the other end. You can see a video of a longitudinal wave in a spring at this URL:http://www.youtube.com/watch?v=ubRlaCCQfDk.

Compressions and Rarefactions

Notice in the Figure above that the coils of the spring first crowd closer together and then spread farther apart as the wave passes through them. Places where particles of a medium crowd closer together are called compressions, and places where the particles spread farther apart are called rarefactions. The more energy the wave has, the closer together the particles are in compressions and the farther apart they are in rarefactions.

P Waves

Earthquakes cause longitudinal waves called P waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions away from the disturbance. P waves are modeled in the Figure below.

Q: Where are the compressions and rarefactions of the medium in this model of P waves?

A: The compressions are the places where the vertical lines are closest together. The rarefactions are the places where the vertical lines are farthest apart.

Summary

·        A longitudinal wave is a type of mechanical wave, or wave that travels through matter, called the medium. In a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction that the wave travels.

·        Places where particles of the medium crowd closer together are called compressions. Places where particles of the medium spread farther apart are called rarefactions.

·        Earthquakes cause longitudinal waves called P waves, which pass through underground rocks.

Explore More

Use these resources of longitudinal waves to answer the questions that follow:http://www.physicsclassroom.com/mmedia/waves/lw.cfm and http://www.physicsclassroom.com/Class/waves/u10l1c.cfm.

1.      What is a wave?

2.      Describe a transverse wave.

3.      Define and describe a longitudinal wave.

4.      How is energy transported in a longitudinal wave?

5.      Describe a longitudinal wave flowing through a slinky.

6.      Give examples of a longitudinal wave.

Review

1.      What is a longitudinal wave?

2.      Draw a sketch of a longitudinal wave. Use arrows to show the direction of the wave and the direction of the vibrating particles of the medium. Add labels to identify the compressions and rarefactions.

3.      Describe P waves.

Surface Wave

Explores waves on the surface of a medium.

·        Define surface wave and give an example.

·        Describe the motion of particles of the medium in a surface wave.

·        Explain why ocean waves break near the shore.

This immense wall of moving water gives the surfer an amazing ride. The swelling surf raises him up and pushes him forward as though he’s as light as a feather. All he needs to do is keep his balance on the surfboard. The incredible power of the wave will do the rest. Ocean waves like this one are examples of surface waves.

Waves on the Surface

A surface wave is a wave that travels along the surface of a medium. The medium is the matter through which the wave travels. Ocean waves are the best-known examples of surface waves. They travel on the surface of the water between the ocean and the air.

Q: What do you think causes ocean waves?

A: Most ocean waves are caused by wind blowing across the water. Moving air molecules transfer some of their energy to molecules of ocean water. The energy travels across the surface of the water in waves. The stronger the winds are blowing, the larger the waves are and the more energy they have.

How the Medium Moves

A surface wave is a combination of a transverse wave and a longitudinal wave. A transverse wave is a wave in which particles of the medium move up and down perpendicular to the direction of the wave. A longitudinal wave is a wave in which particles of the medium move parallel to the direction of the wave. In a surface wave, particles of the medium move up and down as well as back and forth. This gives them an overall circular motion. You can see how the particles move in the Figure below and at this URL: http://www.youtube.com/watch?v=7yPTa8qi5X8

Why Waves Break

In deep water, particles of water just move in circles. They don’t actually move closer to shore with the energy of the waves. However, near the shore where the water is shallow, the waves behave differently. Look at the Figure below. You can see how the waves start to drag on the bottom in shallow water. This creates friction that slows down the bottoms of the waves, while the tops of the waves keep moving at the same speed. The difference in speed causes the waves to get steeper until they topple over and break. The crashing waves carry water onto the shore as surf.

Q: In this diagram of a wave breaking near shore, where do you think a surfer would try to catch the wave?

A: The surfer would try to catch the wave where it starts to steepen and lean forward toward the shore.

Summary

·        A surface wave is a wave that travels along the surface of a medium. Ocean waves are the best-known examples of surface waves.

·        In a surface wave, particles of the medium move up and down as well as back and forth in an overall circular motion. The particles don’t actually move closer to shore as the waves pass through.

·        In shallow water close to shore, waves start to drag on the bottom of the water. The bottoms—but not the tops—of the wave slow down because of friction. This causes the waves to steepen until they break and fall over, carrying water onto the shore as surf.

Explore More

At the following URL, read the article about surfing and ocean waves. Then answer the questions below. http://www.exploratorium.edu/theworld/surfing/makingwaves.html

1.     Describe how you can simulate ocean waves in a bathtub,

2.     Why may ocean waves get bigger as they travel farther away from a storm?

3.     Identify three factors that contribute to the formation of good surfing waves.

Review

1.     What is a surface wave?

2.     Describe how particles of the medium move in a surface wave.

3.     Explain how surface waves change when they reach shallow water near shore.