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How do waves carry energy?

How do waves carry energy?

Introduction: (Initial Observation)

Any sudden pressure to the surface of water creates a wave. You will see an elevated circle of water starts from the point of pressure and enlarges and finally disappears. The same is for the sound and light waves. Creation of a sound requires energy.

Created sound travels and it’s energy vibrates someone’s ear drums or some microphone magnet, where sound energy is converted again to mechanical energy or electrical energy. The fact that we can hear a sound or see a water wave indicates that sound carries energy! But how does it happen? How do waves carry energy?


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about different types of waves and the way they can be created. Read books, magazines or ask professionals who might know in order to learn about transforming different types of energy to each other. (Focus on converting some wave energy to other types of energy or vice versa). Keep track of where you got your information from.

Following are some helpful information:

You can get energy from waves

As wind travels across the water’s surface, it pushes against the water and energy in the wind is absorbed by the water.

Wave power plants use the kinetic energy of the moving waves to make electricity.

About 200 years ago, the first machines for using the wave energy were developed. These single low power machines have been developed into wave power plants.

There are different ways of using wave power. Two machine types are explained below.

The first machine type is the so called “Salter-Duck” (invented in 1973 by Stephen H. Salter).

The “Salter-Duck” consists of a series of such cams. The cams are located on the surface of the water. The waves push on the cams and the cams oscillate.

The movement of the cams drives special pumps. Liquid, like water or oil, is pumped in the same way with high pressure. Electrical energy is generated by hydraulic motors using the high pressure of the liquid.

Another way of converting wave energy is the “Wave-converter” (by J.Masuda).

During the falling wave there is a vacuum in both chambers. The left valve opens and air is sucked through the left valve. In order to get into the right chamber the air has to pass the propeller. The propeller rotates and drives the generator.

During the rising wave the air is compressed. The left valve closes and the right valve opens. The air from the left air chamber has to pass the propeller. The air flow drives the propeller and the generator transforms the rotation into electricity.

The number of condensations or rarefactions produced by a vibrating object each second is called the frequency of the sound waves. The more rapidly an object vibrates, the higher will be the frequency. Scientists use a unit called the hertz to measure frequency. One hertz equals one cycle (vibration) per second. As the frequency of sound waves increases, the wavelength decreases. Wavelength is the distance between any point on one wave and the corresponding point on the next one.

Most people can hear sounds with frequencies from about 20 to 20,000 hertz. Bats, dogs, and many other kinds of animals can hear sounds with frequencies far above 20,000 hertz. Different sounds have different frequencies. For example, the sound of jingling keys ranges from 700 to 15,000 hertz. A person’s voice can produce frequencies from 85 to 1,100 hertz. The tones of a piano have frequencies ranging from about 30 to 15,000 hertz.

Sound Waves

Exploring Sound

Sound is a physical action that stimulates the sense of hearing.

Ring a bell or clap your hands.

The sound we hear is caused by vibration of the air.

In humans, hearing takes place whenever vibrations of frequencies between 15 and 20,000 hertz reach the inner ear. (Hertz is a unit of frequency equaling one cycle per second.)

How do these vibrations reach the inner ear?

Such vibrations reach the inner ear when they are transmitted through air as a wave. The term sound is usually restricted to airborne vibrational waves

Everyday sounds are caused by minute movements of the tiny molecules of the gases that make up the air around us. Sound we hear is caused by vibration of the air. However, vibration can be transmitted through any substance, where solid, liquid, or gas, in which adjacent particles of the substance come into contact. A single pulse can be started off by a single event – when hands are clapped and the air between them is forcibly compressed. Regular pulses can be started by an object that is vibrating, such as a stretched wire inside a piano. The number of pulses in the air matches the rate of vibration in the wire. The number of vibrations (or cycles) per second gives the frequency of the sound.


Sound waves are vibrations in matter. They can only travel through matter – air, water, glass, steel, bricks and mortar; if it can be made to vibrate, sound will travel through it.

Demo: Human Chain
Push vs. Pull
Push is the compression phase of a sound wave.
Pull corresponds to the expansion phase of a sound wave.

Tight vs. Loose Connection
A loose connection is like a sound wave traveling in air – the molecules are not close packed so the sound does not travel as efficiently.
A tight connection corresponds to sound traveling through a metal where there is a lattice of molecules which allow for a very efficient transfer of energy.


Demo: Slinky
Longitudinal Wave
A sound wave is a longitudinal wave. As the energy of wave motion is propagated outward from the center of disturbance, the individual air molecules that carry the sound move back and forth, parallel to the direction of wave motion. Thus, a sound wave is a series of alternate compressions and expansions of the air. Each individual molecule passes the energy on to neighboring molecules, but after the sound wave has passed, each molecule remains in about the same location.


Experiment: Creating Waves
(Activity #2 in Sound and Tone kit)
Equipment Needed:

  • tuning fork
  • yellow cup
  • water

Wavelength, Frequency, and Amplitude

When transmitting sound pulses, air molecules oscillate back and forth. One way of representing this motion is to record the position of a molecule (or a person in the case of our human chain) at each moment in time. Sound represented this way traces out a wave-shape.

The distance between high pressure points in the wave is the wavelength of the sound. The number of waves that passes a point each second is the frequency of the sound. The greater the frequency the higher the pitch of the sound. The greater the movement of the air molecules, the more pressure and thus the greater the amplitude (height) of the wave and the louder the sound.

Humans hear primarily by detecting airborne sound waves, which are collected by the auricles. The auricles also help locate the direction of sound. After being collected by the auricles, sound waves pass through the outer outerauditory canal to the eardrum, causing it to vibrate. The vibrations of the eardrum are then transmitted through the ossicles, the chain of bones in the middle ear.

As the vibrations pass from the relatively large area of the eardrum through the chain of bones, which have a smaller area, their force is concentrated. This concentration amplifies, or increases, the sound. When the sound vibrations reach the stirrup, the stirrup pushes in and out of the oval window. This movement sets the fluids in the vestibular and tympanic canals in motion. To relieve the pressure of the moving fluid, the membrane of the oval window bulges out and in. The alternating changes of pressure in the fluid of the canals cause the basilar membrane to move. The organ of Corti, which is part of the basilar membrane, also moves, bending its hairlike projections. The bent projections stimulate the sensory cells to transmit impulses along the auditory nerve to the brain.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to discover and demonstrate “How waves carry energy?” or “How can energy be transferred in the form of wave?”

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that energy can be transferred from one molecule to the next in the form of a small vibration. If we think of molecules as small marbles, some source of energy may initiate a move in one marble. Then one by one, each marble will hit the other marble passing its energy down the line. When the last marble receives this energy, it will roll away leaving all the other marbles in their original positions. This passing of energy from marble to marble closely mimics the way a sound wave is produced. When we hear a sound, we don’t feel air blowing toward our ears. So not all air molecules are moving toward us, instead air molecules vibrate one after the other until such vibration will reach to the air molecules inside our ears.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

In this experiment we will test how the energy can transfer from one object to the other in the form of the wave. We will use still balls or marbles to represent small molecules of different material. We try to see how energy can pass from molecule to molecule…


  1. Take 4 marbles and line them up in a straight line on a table or other flat surface. Make sure the marbles are all touching. You can place two rulers on two sides of your row of marbles to make sure the marbles stay in a straight line.
  2. Take a 5th marble and thump it so it hits one of the end marbles. And see what happens.

What we expect? There are two possibilities. One is that all four marbles will start to roll in the direction of the force caused by the fifth marble. The other possibility is that the energy will travel from one marble to the adjacent marble without them moving until it gets to the last marble. The last marble can not transfer the energy to anything else, so only the last marble will start to move. The result can be helpful in determining how does the energy travel in the form of a wave. In real life we can think of any air molecule, water molecule or any other molecule as a very small marble.

Experiment 2:

The purpose of this experiment is to see if a water wave caused by the wind will actually move the water itself in the direction of the wind.


  • 1 large, flat pan, about 4 or 5 inches deep, (dishpans or larger)
  • 1 electric table fan or paper fan or small battery operated fan
  • buckets or jugs for filling the pans with water
  • food dye (optional)
  • 5 large marbles or ball bearings for each group

Use a pan that does not have vertical sides.

Vertical sides will reflect the waves so you may not see the direction of waves.


  1. Put the pan on the table and fill it up with 2-3 inches of water.
  2. About 1 foot from each pan (on a narrow side), place an electric fan or have a student hold a paper fan facing the pan.
    (If you use a small battery operated fan, bring it closer to the water.)
  3. Predict what will happen when the fan blows across the water’s surface. After you have made predictions, let the fan blow at a low speed.
  4. Report the results. Were there waves? Did the water bunch up at the far end of the pan? Did the water slosh out of the pan? Then speed up the fans and report again. Make sure you don’t run fans so quickly that water sloshes out of the pans. (It might slosh out with the fan at high speed because the energy in the waves can’t transfer into the pan’s wall readily.)
  5. Discuss the connection between the wind and the waves in your report. Guess why the water didn’t bunch up at the far end of each pan.
  6. Place on drop of food dye in the water, in the center of the pan. Start the wind again. Does the wave carry the dye to the end of the pan? What do you learn about the nature of wave by looking at the food dye in the water?


This experiment does not have a measurable result, so you will not have a data table or a graph for it. Before you do the experiment you may expect two different observation:

  • One possible observation is that the water moves with the wave and carries the food dye with itself.
  • Another possible observation is that the water does not move with the wave and the dye stays in the same area.

You will know the right answer after you do the experiment.

Materials and Equipment:

List of material can be extracted from the experiment section

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


The question of this project does not require calculations.

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

The sounds we hear every day are formed by the vibration or movement of air. Basically what happens is sound makes tiny particles in the air, called molecules , bump into each other. The molecules bump into each other compressing and then expanding to cause the wave to move like a falling column of dominos. This vibration of molecules is passed from molecule to molecule until it reaches our ears where we then ‘hear’ the vibrating air.

Additional conclusions:

1. Since sound is caused by the vibration of an object it stands to reason that there must be some object for sound to exist. Hence, in the empty realm of outer space – there is no sound.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.