How does a compass work? Understanding North and South Poles

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SWBAT explain and draw a diagram of the north and south poles of a magnet.

Big Idea

Playing with magnets can be fun, but understanding that the magnet has poles is also fascinating. It helps them understand how the poles of the Earth and gives them an understanding of a compass.

What We Know

5 minutes

In a previous lesson we played and explored with magnets. To begin today, I ask the class to get out their science journal and review their notes from their magnet play. I give my students about three minutes to review their notes before we talk about our prior learning. When I lead the discussion I focus on the repel and attract qualities of objects and any other observations that were made. 

Watch and Discuss

10 minutes

As we move to our new content learning, I have pre-made the magnet pendulum. This is four to five magnets stacked inside camera film cases. I have then tied a piece of yarn to the cases so that they swing like a pendulum. 

I model what happens when I swing the magnets freely and uneven. Immediately the magnets attract and are stuck together. We discuss what we observed. I then do the same thing but I model how careful I am going to be to swing the magnets evenly. Before I do, I ask them to predict what might happen. I conduct the experiment and we discuss how the two cases seem to bounce away from each other.  

Magnet Play

10 minutes

We briefly discuss what we saw and I hand out magnets to pairs of students. As I do this, I ask the pairs to try to attract and repel the two magnets. I ask them to write down their observations into their science journal. I then explain that every magnet has a north and south pole. I then ask the students to try to determine if like poles attract or repel each other. 

We have a discussion on their findings and determine that a north and south will attract, where a south and south will not. As we discuss, I really try to develop the science vocabulary behind magnets with the words repel and attract. Understanding the importance of the words and how they explain the way in which magnets work will help them understand how compasses work. After discussing, we draw repel and attraction into a diagram and add it to our science journals. 


Compass and Closing Concepts

15 minutes

Next, I hand out a few compasses. I have these groups explore and play with them trying to see what happens to the needle as they move around the room. I give a hint that the compass works like the magnets did. I then ask them to discuss how the compass might work. 

I then explain that the Earth also has north and south poles. I ask the class to explain what this means now that they understand this concept using the magnets. As a class, they begin to discuss that the Earth must be a giant magnet. I confirm this thinking. I then ask how does this then make the compass work. This takes more prompting, but students begin to understand that due to the magnetic force, the needle finds north. I now have them play with compass to confirm this idea. 

Finally, I have them write a few sentences about how magnets can be connected to the Earth and the use of a compass into their science journal.