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Use Super-strong Magnets to Make a Simple Motor

Abstract

In this science project, you will build what might be the world's simplest motor. It has just four basic parts: magnets, a battery, a screwdriver, and a short piece of wire. It takes only minutes to assemble, but it provides a wonderful device to explore how electricity and magnetism combine to produce a fast-spinning motor.

Summary

Areas of Science
Difficulty
 
Time Required
Average (6-10 days)
Prerequisites
Some familiarity with basic electronics and physics would be helpful, but is not required.
Material Availability
Specialty items are required. See the Materials and Equipment list for details.
Cost
Average ($50 - $100)
Safety
Minor injury is possible. Wear safety goggles at all times. Be sure to read the important safety notes at the beginning of the Experimental Procedure before you begin.
Credits

David B. Whyte, PhD, Science Buddies

Objective

The objective of this science project is to make a very simple homopolar motor and to determine how the size of a neodymium magnet affects its rate of rotation.

Introduction

An electric motor is a device that uses electrical energy to produce kinetic energy. In a toy car, for example, the electrical energy in the battery is converted into the kinetic energy that spins the wheels and makes the car move forward. Electric motors work by taking advantage of the interaction of magnetic fields and current-carrying conductors. In this science project, you will build what might be the world's simplest motor.

The motor has four parts: a battery, a piece of copper wire, a small screwdriver, and neodymium magnets. Neodymium magnets are much stronger than the "normal" magnets you might have on your refrigerator. The neodymium magnets will be attached to both sides of the battery, and the battery will be suspended from the point of the screwdriver (see Figure 1). Because the magnet is so strong, the attractive force is sufficient to hold the suspended weight of the battery and the magnet (note: you can read more about magnets in the Science Buddies Electricity, Magnetism, & Electromagnetism Tutorial). The battery will start to spin when the wire is connected between the screwdriver and the edge of the stack of magnets below the battery, producing a current. A laser tachometer will measure the rate of rotation. See the setup in Figure 1.

Homemade electric motor next to a diagram of an electric field

The homemade electric motor is made from household materials. The motor spins due to magnetic forces highlighted in the diagram to the right. The electric motor is built from a screwdriver, battery, magnets and copper wire. A piece of reflective tape with a laser tachometer is used to measure the motors rotations. The diagram on the right shows a circular magnetic field viewed from above. As current flows towards the edge of the magnet, a force is generated at the edge of the magnet with its direction dependant on the direction of the current.


Figure 1. The panel on the left shows the motor and the laser tachometer. The motor consists of a small screwdriver, a length of copper wire, a C battery, a piece of reflective tape (for the laser tachometer reading), and neodymium magnets. The panel on the right focuses on the axis through the magnets. The battery and the magnet spin because of a tangential force created by the flow of a current through the magnet. The magnitude of the force is given by the product of the current, I, the length, L (which, in this case, equals the radius of the magnet), and the magnetic field strength, B.

In order for the battery and magnets to move, there has to be a force acting on them. The force that causes the battery and magnets to move results from the interaction of the magnetic field produced by the magnets with the current that flows through the wire, the magnets, and the battery as the wire touches the magnets. You would usually avoid connecting the two poles of a battery with a wire, since this discharges the battery very quickly. However, in this case, it is desirable to have a large current to maximize the interaction of the magnetic field with the current.

The force acting on the magnet to make it spin is called the Lorentz force. The Lorentz force can be more precisely defined as the force, F, acting on a particle with an electric charge, q, and moving with a velocity, v, in a magnetic field with strength B. The equation for the Lorentz force when the magnetic field is perpendicular to the current is shown below in Equation 1:


Equation 1:

F = qvB

This equation states that the force is equal to the product of the charge, q, the velocity, v, and the magnetic field strength, B.

How do you convert this equation, which describes the force on a moving charge, to one that uses familiar electronic terms, such as current? The velocity term seems especially troubling, since there's no way to measure it, but you can get rid of the velocity term by replacing it with the distance at which the charge travels (L) divided by time (t).


Equation 2:

v = L/t

In words: Velocity = Distance, L, divided by time, t

Substitute Equation 1 into Equation 2 to get Equation 3:


Equation 3:

F = qLB/t = (q/t)LB

In other words, the Lorentz force equals the product of the charge, the length the charge travels, and the magnetic field strength, divided by the time it takes the charge to move the distance L.

Current, I, is defined as charge per unit time:


Equation 4:

I = q/t

This equation states that if you were to look at a point in the wire (or screwdriver or magnet or battery) and measure how much charge passed through over a certain time period, the current at that point would equal the charge divided by the time.

Substituting Equation 4 into Equation 3 gives us the Lorentz equation in familiar electronic terms.


Equation 5:

F = ILB

This equation states that the force on an object of length L, carrying a current I, in a magnetic field B equals the product of the current, the length of the current, and the strength of the magnetic field.

As you can see in Figure 1, the force is directed perpendicular to the edge of the magnet. This tangential force causes the magnet to start spinning.

For this electronics science project, you will assemble the motor described above. This kind of motor is referred to as homopolar, because unlike regular electric motors, it does not have alternating polarity. You will determine how adding more magnets affects the rate at which the motor spins. The rate of spin can be accurately measured using a laser tachometer. The tachometer measures the rate at which laser light is reflected back to it from reflective tape attached to the spinning battery.

Terms and Concepts

Questions

Bibliography

You can also try searching YouTube for videos of homopolar motors. Some versions have the wire moving and the magnet staying fixed.

Materials and Equipment

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

Safety Notes about Neodymium Magnets:

Neodymium magnets are very strong. Adult supervision is recommended when using them. Do not let the magnets slam together. They may pinch your fingers or crack. Keep them away from small children, pets, credit cards, and pacemakers.

Preparing the Experimental Setup

  1. Caution: Because the homopolar motor has moving parts, you should wear safety goggles at all times.
  2. Label the batteries 1–4 with the permanent marker.
  3. Attach a small piece of reflective tape to each battery.
    1. The reflective tape is included with the laser tachometer that is listed in the Materials and Equipment section.
  4. Cut about 10 cm of copper wire.
  5. Wrap one end of the wire around the screwdriver four or five times, about 3 cm from the tip. See Figure 1 in the Introduction.
  6. Attach one neodymium magnet to the positive side of the battery labeled 4. The positive side is marked with a "+" on one end. Center the magnet over the battery.
  7. Attach four magnets on the negative side of the C battery.
    1. These magnets should have the same polarity as the magnet that is already attached.
    2. Center the magnets.
  8. Touch the tip of the screwdriver to the single magnet attached to the positive pole of the battery.
  9. Hold the battery up so that the battery and magnets are hanging from the screwdriver.
  10. Touch the free end of the copper wire to the lower stack of batteries.
    1. Touch the magnet in the stack that is closest to the battery.
  11. The battery should start to spin.
  12. Measure the rate of rotation using the laser tachometer.
    1. Follow the directions that came with the tachometer to learn how to operate it.
    2. Have your helper measure the rate and record it in your lab notebook.
  13. Avoid running the motor continuously. The battery should not get hot.
  14. Remove the magnets from the battery labeled 4.

Measuring the Maximum Rate of Rotation with Additional Magnets

  1. Attach one neodymium magnet to the positive side of the battery labeled 3.
  2. Attach three magnets on the negative side of the C battery labeled 3.
    1. These magnets should have the same polarity as the magnet that is already attached.
  3. Repeat steps 6–13 of the previous section to obtain the maximum rate of rotation with three neodymium magnets attached to the negative pole of the battery.
  4. Remove the magnets from the battery labeled 3.
  5. Attach one neodymium magnet to the positive side of the battery labeled 2.
  6. Attach two magnets on the negative side of the C battery labeled 2.
    1. These magnets should have the same polarity as the magnet that is already attached.
  7. Repeat steps 6–13 of the previous section to obtain the maximum rate of rotation with two neodymium magnets attached to the negative pole of the battery.
  8. Remove the magnets from the battery labeled 2.
  9. Attach one neodymium magnet to the positive side of the battery labeled 1.
  10. Attach one magnet on the negative side of the C battery labeled 1.
    1. The magnet should have the same polarity as the magnet that is already attached.
  11. Repeat steps 6–13 of the previous section to obtain the maximum rate of rotation with one neodymium magnet attached to the negative pole of the battery.
  12. Perform the entire procedure two more times. Performing three trials ensures that your results are accurate and repeatable.

Graphing Your Results

  1. Average the maximum rates of rotation for one, two, three, and four magnets.
  2. Make a graph with the number of magnets on the x-axis and the maximum rate of rotation on the y-axis.
  3. Discuss the factors that affected the speed of rotation you observed.
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Variations

  • Try other sizes of magnets. How does the diameter affect the performance?
  • With four magnets on the negative terminal, measure the rate of rotation when you touch the copper wire to each of the four magnets. What do you predict will happen?
  • Devise a stand for the spinning motor so that you do not have to hold it.
  • Use a multimeter to measure the current in the circuit.
  • Devise a way to measure the Lorentz force.
  • Identify sources of unwanted variation in the results and design a procedure that avoids them.

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MLA Style

Science Buddies Staff. "Use Super-strong Magnets to Make a Simple Motor." Science Buddies, 7 May 2021, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p065/electricity-electronics/use-super-strong-magnets-to-make-a-simple-motor. Accessed 22 May 2022.

APA Style

Science Buddies Staff. (2021, May 7). Use Super-strong Magnets to Make a Simple Motor. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p065/electricity-electronics/use-super-strong-magnets-to-make-a-simple-motor


Last edit date: 2021-05-07
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