The Push and Pull of Magnets

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Objective

SWBAT describe that there is an invisible magnetic field that surrounds a magnet which is strongest at its poles.

Big Idea

Students will get a visual of the magnetic field that surrounds a magnet and test magnets of various sizes to determine if larger magnets have stronger magnetic fields.

Rationale and Preparation

The Why Behind Teaching This: 

This unit covers standard 5-PS2-1: Support an argument that the gravitational force exerted by Earth on objects is directed down.  During the unit, students will investigate a variety of objects to see that the force of gravity is constant on Earth and pulls things down towards its center.  We will also be investigating a variety of ways to overcome gravity. 

Several of the lessons in this unit are engineering design projects requiring students to follow the steps of the engineering design process to construct a project.  These projects address standard 3-5-ETS1-1: Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost. It also addresses engineering standard 3-5-ETS1-2: Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.  There are also several experiments in the unit which address standard 3-5-ETS1-3: Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.  

This specific lesson addresses standard 3-5-ETS1-3 by requiring students to identify and control variables in an experiment.  The lesson is not directly related to the standard on gravity, but does provide knowledge on others forces that may be acting on an object to oppose the downward force applied by gravity.  

Lesson Goal: 

The goal of this lesson is for students to demonstrate an understanding that there is an invisible force surrounding all magnets, that is strongest at its poles. 

Success Criteria:

Students will demonstrate success on the lesson goal by answering all questions correctly on the exit ticket.  

Preparing for Lesson:

Warm Up:

  • Ziplock bag of iron filings for each group 
  • A small magnet for each group  

Guided Practice: 

Explore: 

  • A ruler for each group 
  • A small magnet for each group 
  • A medium magnet for each group 
  • A large magnet for each group 
  • A paperclip for each group 

Wrap Up: 

Warm Up

10 minutes

Providing a Visual for the Magnetic Field Surrounding a Magnet 

I begin this lesson by providing each group with a Ziplock bag of iron filings and a magnet.  I instruct students to lay the bag flat on one of the desks so that the iron filings are spread out.  I tell them to place the magnet on top of the bag and observe what happens.  

                                            

The iron filings move to show how the magnetic field that surrounds the magnet is strongest at the poles.  I ask students if they think the magnetic field is the same for all magnets, or stronger for larger magnets.  I specify that by "strong" I mean the ability to attract magnetic items better (either more items, or from a farther distance).  The majority of students tell me that it is stronger for larger magnets. We will be conducting an experiment to test this in today's lesson.

Before moving on to the experiment, I ask students what happens when two magnets are next to each other with the same poles facing. This is review from the types of forces lesson earlier in the unit.  Students tell me they push away.  I provide each group with a second magnet.  I have them place it on the bag next to the other magnet so that the same poles are facing each other. I want them to see how the iron filings react to this.  As they move the magnets closer together, the iron filings seem to push back away from the pole so that a gap of empty space is left between the poles.  This provides them with a visual for how a pushing force is exerted when magnets with the same poles face each other. 

                                         

Guided Practice

10 minutes

Setting up the Experiment 

Students take out their notebook so we can begin planning the experiment together.  I provide each student with a prefolded trifold experiment foldable.  I use this style foldable for all experiments because it helps students practice the correct set up for the end of the year science fair project.  I place my notebook on the overhead as a visual for students.  This is a good strategy to help ESE and ESOL students with copying, but also beneficial to any student who struggles with writing or spelling.  I provide all ESE/ELL students with a copy of the experiment steps that have been preciut and placed in a baggie.  Having the steps to just glue in, helps these students focus on the instructions I am giving and the class discussion that takes place.  

We record the question for the experiment in the upper left hand corner of the foldable: Does the size of magnet affect the strength of the magnetic force? I show students 3 magnets, one small, one medium, and one large.  

I explain that they just had the opportunity to see a visual of the magnetic field that surrounds a magnet.  I tell them that during the experiment today, we will determine if the magnetic field surrounding these three magnets is the same, or different.  

I record the start of the hypothesis in my foldable and the students copy it down: If I use a small magnet, medium magnet, and large magnet to attract a paperclip, then I predict the __________________ magnet will have the strongest magnetic force.   I ask how we would know which had a stronger magnetic force and the students tell me that it would attract the paperclip first.  

I record the materials for the experiment as: small magnet, medium magnet, large magnet, paperclip, ruler.  As students copy the list of materials, I pass out a copy of the experiment procedure to each student.  The ESE students already have this but I provide it to all other students to save on time.  There are usually numerous steps in completing the experiment which would take a long time to discuss and copy.  It is important that students are able to focus on my directions as I explain the procedure and are not busy copying.  

As we discuss the steps of the procedure, I stress parts that are control variables so that all groups are sure to keep these the same during their tests.  For example, the placement of the paperclip must be the same for all all groups or they will not get accurate data.  I am also modeling each step of the procedure so that students have a visual of what they will be doing.  This helps set them up for success and prepares them to work independently on the experiment.  

After we go over the steps of the procedure, we draw a data table in the center of the foldable.  The data table for this experiment has 4 columns and 4 rows.  The columns are titled Trial 1, Trial 2, and Trial 3.  The rows are titled Small Magnet, Medium Magnet, and Large Magnet.  

                                             

After drawing the data table, we close the foldable and record all of the variables on the outside.  Based on our discussion, we record the following information:

  • Independent Variable - Size of Magnet 
  • Dependent Variable - Distance from the paperclip when it was attracted
  • Control Variables - paperclip, ruler used, placement of the paperclip, how you move the magnet

                                            


Explore

30 minutes

Conducting the Experiment 

I already have students sitting in groups of 4 in the classroom.  Each group is made up of both girls and boys, one of the students is a higher level student, one regular student, and two students that are ESE and/or ELL.  This set up allows for struggling students to have peers in their group that can help them if they have a question.  

I provide each group with the materials they will need for the experiment and let them get started.  I circulate while students work together to conduct their experiment.  As I circulate, I am making sure that all students are participating and that accurate measurements are being taken for the data, including recording the unit of measure.  I am also questioning, "how is the paperclip pulled towards the magnet without the magnet touching it?"  I want to hear students using the science vocabulary by describing the magnetic field that surrounds the magnet.  The paperclip is pulled towards the magnet once it is close to the magnetic field, not when it touches the magnet. 

                                         

You can see in the video of student testing small magnet that the paperclip was attracted from 3 cm.  The picture above shows the paperclip being attracted to the medium magnet from 1.5 cm.  The video of student testing large magnet shows that the large magnet did not attract the paperclip until 1 cm.   

Wrap Up

10 minutes

Sharing Results 

As groups begin to finish, I ask them to analyze their data and add it to the Class Experiment Sharing Chart. When they add it to the chart, I ask them to circle the magnet that had the strongest force in each trial.  After their data is added, I provide them with a copy of the magnetism exit ticket to work on while other groups add their data.  

                                     

I leave the sharing chart up on the overhead for students to see the results from all the groups.  After everyone has added their data, it shows that all groups, except one, found that the small magnet had a stronger magnetic attraction then the medium and large.  The one group that got different results found that the large magnet had the strongest magnetism. We discussed why this data would not be considered reliable (it was the only group that got different results) before proceeding. 

Discussing Why Size Isn't a Factor in Strength 

When preparing for this lesson I chose the magnets we were using very carefully.  I knew that the large magnet was the weakest out of the three we used.  I wanted students to see that the strength of the magnet is not related to the size, that other factors determine the strength.  I want to use this lesson to activate their scientific thinking.  Make them question, "if size doesn't affect the strength, then what does?"

We discuss the results and I ask students to give me some ideas on what they think might affect the strength of a magnet if it isn't size.  

One student explains: the small magnet is a horseshoe magnet with both poles at the same end. Since the magnetic field is strongest at the poles, maybe that is what makes it stronger.  

Another student says: the medium magnet is very light compared to the other two so maybe it is made of different materials which made it not as strong.  I expand on this by rephrasing that he believes the material of the magnet might affect how strong it is.  

I tell students that they are acting just like scientist.  Sometimes an experiment leads to more questions.  They did not get the results they thought they would so now they have to begin the process over by asking a new question.  For example, if we want to test the idea that the horseshoe magnet is stronger then a bar magnet, we would need to identical magnets, only the shape being different, and test them.  Or if we want to test the material, we find magnets with different compositions, but everything else including size and shape, would need to be the same, and we test those.   

Exit Ticket

Observations were used to assess their ability to work through the scientific method.  The exit ticket given at the end assesses their understanding of the magnetic field and when magnets will repel.   

I was happy to see that all but 6 out of 40 students got the answers on the exit ticket correct.  They did not all show proficiency in the same way, but all that passes showed they know what they were talking about.  The two examples below show correct answers.