Teachers TryScience

· What is a magnet?

· What will stick to a magnet?

· Are large magnets stronger than small magnets?

· Is the earth a magnet?

Tell the students:

· Today we are going to try to answer these questions.

A Short History of Magnets and Magnetism

Tell Students: The following is a story that tells where magnets came from:

A long time ago, Ancient Greeks and Romans were aware of magnetism. They had found a mysterious black stone that made certain metals stick to them. The Greeks and Romans had difficulty explaining these strange happenings, and many legends were created.

Accepting all answers – ask “What is a Legend?”

A legend is a story that people told and passed down to their children.

This legend was about a shepherd from a place called Magnesia. The shepherds carried wooden staffs and covered the ends with iron so that they would not wear out so quickly on the rocky ground. As one shepherd walked with his flock of sheep, he noticed that some of the tiny stones in the soil stuck to the iron tip of his staff. He had a hard time pulling off the stones. He called these stones magnets after his
homeland. (Adapted from Hands on Minds On Science: Magnets)

After reading the story:

· Tell the students that today they are going to become scientists.

· Say: A scientist would want to know more about magnets. So today we are going to investigate magnets in our classroom.

Introduction to the Scientific Method

We are going to pretend that we are scientists who have never seen magnets before. We would like to figure out some rules that tell us how magnets behave. If we have a good set of rules, then we can make up a theory of magnets that will predict what a magnet will do in every situation.

· We begin by doing experiments with magnets and observing what happens. We keep asking questions like “What would happen if ...”, and then making new experiments to get the answer. (Baseball great “Yogi” Berra once quipped that “You can observe a lot by just watching.”)

· After doing experiments for a while, we may see some patterns that keep repeating, so we make a guess for a rule that the magnet seems to be following. This is called a hypothesis.

· Now we want to test our hypothesis and find out if the magnet will keep following our rule.

· We need to think of a new experiment that allows us to use our hypothesis to predict what will happen before we actually do the experiment. To find out if the prediction is correct, we run the experiment and observe what happens.

· If the prediction was correct, our hypothesis might be true and we are happy. If the prediction was wrong, it just means that the rules we made up are not quite right and we need to make up some better ones.

· Even if all the predictions keep coming true, a good scientist will never stop experimenting. Eventually there may be some experiments where the prediction fails and our rules are broken. This is good, because that is the only way we can find better rules to keep improving our theory of magnets.

What Things are Attracted to a Magnet? (Let’s Use the Scientific Method)

We run some experiments using a magnet to try picking up various things. We would like to make up some rules to predict whether or not an object will be attracted to a magnet.

For each thing, we ask the kids to predict if it will be attracted to the magnet and then we try the experiment. We try a crayon, pencil, cork, piece of wood, some plastic, a red rock, rubber band, a slinky, paper clip, bottle opener, anvil.

Now we make a hypothesis – Magnets will attract things made of metal.

We need more experiments to test our hypothesis. We try some metal washers, a nail, a screw, all of which are attracted. Then we try some aluminum – which is not attracted. We try a copper wire – which is not attracted. So our rule that magnets attract metal does not always work.

Next we try an iron meteorite and a piece of iron ore (hematite) – which are attracted.

Now we can make a better hypothesis – magnets attract things containing iron.

This rule works very well, but if we kept doing experiments long enough we would eventually discover that magnets also attract cobalt and nickel. Nickel coins are not attracted, but that is because they don't put the metal nickel in nickels any more.

Activity 1: Magnetic observations

· Distribute one magnet to each student. Brainstorm for descriptive words about magnets. List words on board.

· Demonstrate how a magnetic material is attracted to (“sticks to”) the magnet. Ask for an explanation of the observed phenomenon.

· Develop the concept through limited questioning and answering, that promotes critical thinking.

· Distribute guessing bags to each group. Before any testing occurs, elicit predictions as to which objects will be attracted to the magnet. Record predictions on the board.

· Have students at each group take turns putting the magnet in the bag. Record sorting results.

· Review findings as a class. Through brainstorming, develop the rule for determining if an object is magnetic.

· Direct the students to identify objects around the room to test. Ask them to predict, based on the rule, whether they are magnetic. Record.

· Modify the previous rules.

· Demonstrate the ability of lodestone to attract. Ask for explanations. Discuss natural and manufactured magnets.

· Students will predict what will happen with sand. Record.

· Distribute sand to groups and test.

· Report results. Explanations.

· Demonstrate that iron-enriched cereal is magnetic!

How Does Magnetism Travel Through a Piece of Metal?

· We can put a magnet on the head of a nail and then it acts like a magnet and picks up a screw.

· Using a jar with iron filings, we can see the magnetic force field coming out of the two poles of a ceramic magnet.

· With a horseshoe magnet against the jar, we can see the magnetic field looping from one pole to the other.

· But when the keeper bar is on the horseshoe magnet, the field does not go into the jar any more.

· We can make a hypothesis that the magnetic field coming out of a pole normally spreads out in the air but if some iron is near the pole, then the magnetic field will go into the iron instead.

· When we put a magnetic pole against one end of a U-bolt, the field goes around to the other end to make it act like a magnetic pole and pick up a screw.

Distribute magnets to the groups, along with a box of steel paper clips and steel washers.

§ Predict how many paper clips a particular magnet will attract. Repeat for other magnet types.

§ Record group results on white board. Compare to predictions.

Is There a Difference Between the two Poles of a Magnet?

§ Using four ring magnets on a stick, we can experiment with magnetic poles.

§ Initially, the magnets are all stuck together. When pulled apart, they jump back together.

§ But when we flip one magnet over, it is repelled and floats above the other magnets.

§ So it looks like every magnet has two poles and they behave differently – one pole will be attracted to another magnet and the other pole will be repelled.

Why Does a Magnetic Compass Always Point North?

§ We use the magnetic globe dipped in iron filings to show how the earth acts like a huge magnet.

Use a Compass to identify the Two Poles of a Magnet

§ The north end of the compass points to the south pole of a magnet.

§ The south end of the compass points to the north pole of a magnet.

Theory of Magnetic Attraction and Repulsion

§ We discover that opposite poles attract and like poles repel.

Groups use paper sheets, iron filings and bar magnets to explore magnetic fields.

· Distribute paper to groups.

· Distribute bar magnets to groups. Direct students to place magnets 1"- 2" apart, oriented so that they attract or repel.

· Ask students to predict what will occur when iron filings are poured on the paper over the area where the magnets are located. Recall the rule(s) previously developed. Record the predictions.

· Pour iron filings on the paper. Have the students observe and record the results.

· Groups report their results to the class and explain the magnetic field phenomenon.

What Did We Learn?

· Were you surprised by any of the objects interactions with the magnet?

· Can you make a magnet with one pole?