## Earth Movers and Shakers Grades 7-9

When we look back in history we see that many discoveries in science are put to practical use. For instance, Archimedes' famous discovery of the lever in prehistory was later applied to the invention of weightlifting machines, such as crowbars, car jacks, and teeter totters. Isn't it miraculous that one ingenious idea can grow into so many inventions! This lesson, in two parts, teaches students the scientific law of the lever, and its application to mobiles and crowbars.
Eureka! #12 "The Lever"
TV Ontario
(919) 380-0747
Challenge of The Unknown #7 "The Master Builders of Stonehenge"
National Educational Telecommunications Association
(803)799-5517
Students will be able to:
• Define a simple machine, and identify six examples of simple machines
• Formulate a hypothesis about how a lever works
• Draw a picture to show how levers work
• Explain the application of the law of the lever to solve problems about levers
• Demonstrate Archimedes' law in creating a mobile
• Evaluate multiple hypotheses about how Stonehenge was built.
For Each Student Group (2- 3 students):
• Wooden dowel
• Metric ruler
For Class:
• Inclined plane
• Lever
• 100-newton weights
• Newton spring scale
• Meter stick
• Earth Movers Worksheets 1 & 2 *
* Located at the end of the lesson.
Vocabulary:
• Machine - that which changes the force you need to do something
• Inclined plane - a flat sloping thing
• Force - a pull or push that causes motion
• Lever- a bar, such as a teeter totter
• Fulcrum - a point on which a lever is placed

### Part I - Archimedes' Lever

TEACHER: Who am I? I was born in Syracuse on the island of Sicily. I discovered the law of the lever. I am famous for the quote: "Give me a fulcrum on which to rest, and I will move the earth." (Archimedes. He was a Greek philosopher and inventor who lived in ancient times.) Besides the lever, Archimedes also invented other machines, including the catapult, the pulley, and the Archimedian screw, a type of pump. In the lesson today, we will learn about how a teeter totter works. Later on, we will use the teeter totter to do some hard work.

TEACHER: What comes to mind when I say the word "machine"? Ask a volunteer to write the vocabulary words on the board. Now try to define the word "machine." (A machine is something that helps you use your energy more effectively.) There are six so-called simple machines. One of the simplest machines is this "flat sloping thing." Point to the toy inclined plane. What does a physicist call it? (An inclined plane.) Give me another example of a simple machine. Ask students to identify all six types of simple machines. Think of the advantage of using a simple machine, for example this inclined plane. We need a volunteer to demonstrate for the class the mechanical advantage of the inclined plane by moving this 100-gram mass. Be able to tell the class the advantage of moving something with this simple machine. (Inclined planes or any simple machines allow you to trade increased distance for decreased effort. By moving something through a longer distance, you can lessen the effort or the force you need to move it.) OBJECTIVE 1.
It is very important to give students a focus for viewing. This helps them focus their attention on the lesson objectives. This way students learn that video is not solely for their entertainment.

TEACHER: What is this? (Point to the toy lever/teeter totter) Let's watch a video to observe how a teeter totter really works.
VIDEO: Eureka! #12 "The Lever"

START video at the title "The Lever."
PAUSE video after you hear "There's an easy way you could have avoided that."

TEACHER: Generate two different hypotheses about what you could do to keep yourself from flying off the teeter totter. Watch the video carefully to check your hypotheses.

RESUME video.
PAUSE video after you hear the sentence "Both ways boil down to the same thing."

TEACHER: What are two ways you could balance on the teeter totter? (One way is you could ask the big guy to move nearer and nearer to the middle of the teeter totter. Or, you could make a little adjustment in the teeter totter before he sits down on it. Either way you could balance.) Listen carefully for what we call the support that the teeter totter is resting on.

RESUME video.
PAUSE video after you see the word "fulcrum."

TEACHER: What is the fancy word that scientists use? (Fulcrum.) Think about the secret of successful teeter tottering or balancing with someone who is heavier than yourself. Now, watch the video to verify your hypothesis.

RESUME video.
PAUSE video when you see the weight.

TEACHER: So, what is the secret of successful teeter tottering? (The distance between the heavier person and the fulcrum is less than the distance between the lighter person and the fulcrum.) OBJECTIVE 2.

TEACHER: Look at Earth Movers 1 (worksheet No. 1), and solve problem No. I. You want to balance a 100-newton weight with another 100-newton weight. You place one of the weights 2 meters from the end of the fulcrum. Where do you place the other weight? Watch the video to verify your answer.

RESUME video.
PAUSE video after you see the words "2 meters."

TEACHER: We need a volunteer to demonstrate the problem for the class using the model teeter totter. (The volunteer must place the weights at an equal distance from the fulcrum, let's say 2 meters.)

TEACHER: Solve problem No. II on your worksheet. What if you want to balance the 100-newton weight with one that's twice as heavy? Place the 100-newton weight at one end of the fulcrum. Where do you place the heavier weight? Draw a picture to show the positions of the two weights. (Allow students about one minute to complete the problem.) We need a student to demonstrate his answer to the class using the model teeter totter. OBJECTIVE 3

TEACHER: Now let's watch the video to observe how Rosco solves the problem.

RESUME video.
PAUSE video after you hear, "you exert a force of 100 newtons through 1 meter in order to lift a weight of 200 newtons through 1/2 meter," and you see the equation 100N x 1m = 200N x 1/2m. Hold the equation on the screen.

TEACHER: Compare your solution with Rosco's. Did you get it right? We have learned that "what you win on the force you lose on the distance." Let's demonstrate the principle using the inclined plane. Read problem No. III on your worksheet.

Rosco lifts a 100-newton weight straight up through 1 meter. In an effort to save your force, you pull the weight through 2 meters along the inclined plane. How much force do you need to move the weight? (Ask a student to try it using the model inclined plane. He or she should observe that it requires a force of 50 newtons, or half the force.) If you double the distance, you halve the needed force. This is true whether you use an inclined plane or a teeter totter. Where did you place the 200-newton weight to balance the 100-newton weight on the teeter totter? (You placed the weight half the distance to the fulcrum, since it has double the force.) So, what you win on force you lose on distance. This is the principle of both the inclined plane and the teeter totter. OBJECTIVE 4.

TEACHER: Let's return to the video. I want you to listen carefully for the scientific name for a teeter totter, and the principle of how it works.

RESUME video.
STOP video at the end.

TEACHER: What word do physicists use to mean the same as a teeter totter? (A lever.) What is the principle of the lever? ("The longer the arm of the lever to which force is applied, the less that force need be.") Did anyone hear the name of the famous person who discovered it? (Archimedes.) Let's hear Archimedes' law one more time. Be able to recite his law.

REWIND video to the place just before Archimedes' famous quote.

STOP video after the quotation has played through.

TEACHER: We need a volunteer to write the quote on the board. EUREKA! We have discovered the law of the lever.
TEACHER: Let's use Archimedes' law of the lever to make a mobile. You will need the following materials: a lever arm, thread, and an assortment of colored glass beads. Your challenge is to construct a mobile from these materials. Make the mobile as simple or as fancy as you like. There is only one rule that you must always obey when you create a mobile. What is the rule? (Archimedes' law of the lever.) Allow students one class period to construct their mobiles. Hang them around the classroom for everyone to see. Construct a large banner with Archimedes' famous quote, "Give me a fulcrum on which to rest, and I will move the Earth." OBJECTIVE 5.

The teacher may use his or her discretion at this point in the lesson to use the video Return to the Art Maker #3, "Mobiles."

### Part II - Monumental Efforts

TEACHER: Identify this historic site. First clue. It is located in England, and was built in the Stone Age about four thousand years ago. Second clue. On any day you can see a number of people standing around and looking a little puzzled at a circle of great big stones. What is it? (The historic site is Stonehenge.) Stonehenge is one of the greatest engineering works of prehistoric man. But, these master builders did not leave a record of their work. So, no one knows for sure how and why Stonehenge was built.
VIDEO: Challenge of the Unknown #7 "The Master Builders of Stonehenge"

TEACHER: Let's watch a video to learn what the experts think about these gigantic stones.

START video at the begining.
PAUSE video after you hear the words "thousands of years ago these stones were raised to form Stonehenge. Why?"

TEACHER: Think about why Stonehenge was built. I want you to generate at least two hypotheses. (Allow students one to two minutes to write their hypotheses.) Now, listen carefully to check your hypotheses with Professor Atkinson, who has some ingenious ideas about these great stones.

RESUME video.
PAUSE video after you hear the words "this does not make them temples of sun worship."

TEACHER: What were some ingenious ideas or theories that explain why Stonehenge was built? (Stonehenge was built as an astronomical observatory, or a temple of sun worship, since it is aligned with the rising sun at summer solstice.) What other questions does Atkinson ask himself to help him get closer to the facts about Stonehenge? Listen carefully.

RESUME video.
PAUSE video after you hear the words "by whom."

TEACHER: What three questions does he ask himself? (When was Stonehenge built? How was it built, and by whom?) Be able to tell me, which question cannot be answered truthfully?

RESUME video.
PAUSE video after you hear "you cannot simply get into the minds of Stonehenge."

TEACHER: What question is unanswerable? (Why was Stonehenge built?) Why can we not answer this question? (Unless the master builders wrote down the motive for their work, we simply cannot get into the minds of these builders.) Now, listen for how one can get the best possible answers to one's own questions.

RESUME video.

STOP video at the end.

TEACHER: How can one get the best possible answers -- ones that last? (The way to answers that last is, first, do not accept the first answer that occurs to you, and, second, argue with yourself.)
The Ancient Art of Weightlifting:

TEACHER: Challenge yourself by completing Earth Movers 2 (worksheet #2). Think about the following question: How do you suppose Stonehenge was built? Do not accept the first answer that occurs to you. Here are some facts you need to know first: The sandstone rocks called "sarsen" weigh up to 50 tons, and measure over 13 feet tall. They stand upright at Stonehenge. The sandstone was cut from Marlborough Downs, and moved 20 miles to the Stonehenge site. During the Stone Age, trees grew around Stonehenge. Using these facts, generate hypotheses -- your best guesses -- to answer the following questions: How did the builders move the rock? How many people were needed to move each stone? How did they lift and lay the stone in an upright position? (Allow students approximately ten to fifteen minutes to write individual responses. Form teams of 2-3 students and compare responses. Allow 10 minutes. Designate a spokesperson for each team to report to the whole class. Allow 1-2 minutes per team.)

TEACHER: Let's see how the experts answered these questions. How did they move the rock, and how many people were needed for the job? It is thought that about 100 men were needed to move each 50-ton stone, with it resting on a sledge which rolled over tree trunks. They used the simple machine called the ......wheel. (Ask a volunteer to use the toy wheels to show the class how the people used wheels to haul the sarsen stones.) What about lifting the stones once they got to the site? (It is believed that the raising of the stones began with the digging of a large hole. A large tree trunk was then used as a lever to lift the stone, angling it into the pit. When the stone was close to vertical, it was then pulled by ropes wrapped around a tree trunk to get into the upright position.) Ask another student to demonstrate using the toy levers and sarsen stones. OBJECTIVE 6.

TEACHER: Let's apply Archimedes's Law of the Lever to the problem of lifting the sarsen stone. Before we solve the problem, state for me the law of the lever. (The longer the arm of the lever to which force is applied, the less that force need be. Ask a volunteer to write the law on the board.) In math, we can translate the law into the equation for the lever. This becomes pF = qW, where F is the force you need, p is the distance of the force to the fulcrum, W is the weight of the stone, and q is the distance from the rock to the fulcrum. On your worksheet, substitute the numbers into the equation. (W equals 50 tons; q, say, is 1 foot; p, the length of the tree trunk, is 30 feet.) Next, solve the equation for F. (After students have solved the problem, ask a student to solve it on the board.) If we solve for F, we get 1.6 tons. By moving the stone over a much longer distance, the master builders lessened the effort or force they needed to exert. Instead of 50 tons, they had only 1.6 tons.

TEACHER: Wow! They really took advantage of the lever! The average man can lift 200 pounds, which is about 0.1 tons. Tell me, how many men would it take to lift 1.6 tons. (It would take 16 men, since 1.6 tons / 0.1 tons per man =16 men.) Without a simple weight-lifting machine, such as a lever, it would take 500 men to lift the great stones. (500 men x 0.1 tons per man = 50 tons.)

TEACHER: What a monumental effort it was to raise Stonehenge! But remember Archimedes' ingenious idea: "Give me a fulcrum on which to rest, and I will move...?" (Stonehenge, perhaps?) With a good idea and the right invention, anything's possible. Archimedes was really an "earth shaker," and the master builders of Stonehenge? Well... they were truly "earth movers."
Arrange a field trip to a site such as the Pueblo Grande Ruins in Phoenix, Arizona, for a local example of Earth Movers and Shakers. In advance of the field trip, ask students to generate their own questions about the historic site, such as how it was built.

Identify as many levers as you can in the classroom. In your home. Make a large display for your classroom wall illustrating various examples of levers.
History, Science, and Language Arts:
The catapult was a deadly war machine used to batter besieged cities. Instead of using a small force to shift a large mass, it used the opposite principle.

Design and build a catapult that will fire marbles (or paper wads) as far as possible. Chart the accuracy and precision of the results.

Research the Greek philosopher Archimedes. Write a report on his various inventions and the scientific principles of their operation. Try to imagine what Archimedes would invent in today's world.

Research the Druids in connection with Stonehenge. Write a report explaining who they were and when and where they lived.

Art and Science:
Design and construct a wind chime. Explain how the wind chime demonstrates Archimedes' law of the lever. Research the variety of wind chimes.

Create a "find" by burying a number of stones in a pattern. Write down the meaning of the stone arrangement. Ask a student to "unearth" the stones, and decipher the meaning or decide how they were used.

Construct a scale model of Stonehenge.

Math and Science:
Prepare mathematical problems about levers or inclined planes for students to solve.

Return Of The Art Maker #3 "Mobiles"

Laserdisc:
Physics At Work: Simple Machines, Videodiscovery.