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Understanding Doppler Radar: Grades 5-6 Science
To The Teacher:
There are several concepts students will benefit from knowing in order to understand how Doppler radar works when they see it on the nightly news.
The second concept is the Doppler effect.
The best strategy is to introduce the waves they are already familiar with and then compare the waves to the kind of waves they cannot see. This makes another good example of how scientists are able to “see” things that are not visible and how scientists work.
This particular lesson will require a bit more preparation then other lessons in order for the students to make conceptual contact with the ideas they are presented with.
Power Point overheads have been provided to aid you.
The desired outcomes for this lesson are:
- Students will be able to draw a graphical interpretation of how waves behave
- Students will provide examples of how different kinds of waves are used in everyday life
- Students will be able to use pictures and explanations of the pictures to describe the Doppler effect.
- Students will be able to explain what they are looking at when the “weather guy” shows them a picture of radar on the news.
To The Student:
Show Power Point 1
- Almost every night when you watch the news you see images the “weather guy” describes. He tells you whether he expects it to rain or storm. You see pictures of swirling colors he points out to tell you what is coming and how fast. How does he do that? What makes it possible to see the weather arrive before it gets there?
- Shown here is a hurricane approaching the coast of Florida. The more intense the storm the closer to red the color becomes.
Understanding Water Waves
Show Power Point 2
- When you drop a stone into water ripples are produced.
- In it there are different ways of looking at the same event of what water does when a stone drops into a pond. First there is the photograph of water with ripples on the surface. Next to it is an artist’s idea of what the water looks like from the side. Finally at the bottom of the slide is a scientist’s idea of what a wave looks like from the side.
- Explain that scientists often make models that describe what they mean with pictures and words which simplify what they want someone to notice.
- It is also important to notice the ripples move up and down without the water moving back and forth very much by itself.
Understanding Sound Waves
Show Power Point 3 and Click
- Sound moves in the same way, except instead of being able to see it, we hear it.
- Ask the students if the air moves when they hear a sound from across a room.
- Have them understand it is the particles of air that hit each other and pass a wave along to the next bit of air, until the vibration in the air strikes their ear drum like a drum stick striking a drum.
- The greater the number of vibrations the higher the pitch you hear. Even though all the waves travel at the same rate, the number of waves in the same amount of space can vary.
- Waves can have a different number of peaks in the same amount of space because they can have different lengths.
- How fast do sound waves travel? About 760 miles per hour.
- Ask your students to try this: the next time it storms, count how many seconds it takes for them to hear thunder after they see lightning. It takes around 5 seconds for sound to travel 1 mile. That is 2.5 seconds for ½ mile, or a bit more than 1 second to travel ¼ mile.
Show Power Point 4
- The light from the lightning however has enough time to circle the Earth 37 times.
- The first frame shows three different kinds of waves:
- The water waves where the boat moves through the water
- The sounds waves you hear from thunder when sound moves through air
- Light waves when the lightning lights up
- The second frame shows a radar dish which beams out a type of radio wave which you can not see or hear.
- The last frame shows a microwave oven. What does that have to do with lightning and radar? Microwaves travel around the oven in the same way all the other waves travel.
- All of these examples are waves.
Explain How Radar Works
Show Power Point 5
- When the radar sends of a beam of radio waves, it is a lot like you shouting into the distance. If you wait long enough you can hear your own voice because the sound bounces back.
- Shown here in the picture, bats use sound to hunt moths. They emit a high pitched sound which strikes the target. They are then able to know where the moth is and get dinner.
- This is exactly how radar works except instead of a high pitched sound, the radar unit sends radio waves and waits to receive an echo from its target.
The Doppler Effect
- Ask the students to recall the sound of an ambulance siren when it passes by. They may need to be reminded the siren has a high pitch as it comes towards you and a low pitch after the siren passed.
- Explain the reason is that the sounds waves are compacted while a siren comes close. Then they are spread apart as the sound moves away.
Show Power Point 6 and Click
- The boat on the top does the same as it passes through water. The waves in front of the boat are compacted while the waves in the back trail in long ripples behind the boat.
- The animation shows how waves appear traveling through space.
Show Power Point 7
- The final slide shows how radar is bounced off a weather system. When the radar echo returns, the small changes in the radio waves that return to the radar dish can then be compared to the radio waves that were sent out.