Materials Included In Kit

Additional Materials Required

Prelab Preparation

Have students do the pre-laboratory prediction. Almost all students will predict that it will take fewer clips to break the magnetic field when the distance is increased. However very few, if any, will predict the exponential (curved) graph that results. Before beginning the lab, students should make a sketch of what they think the finished graph will look like.

Assembly Instruction

1. Stand the device on a flat surface on its two feet. The T-nut should be in the left block and the magnet in the right block.
2. Thread an eyebolt into the T-nut so that the loop end (eye) of the eyebolt is facing the inside of the assembly.
3. Turn the eyebolt in until it just starts to come out the far side of the T-nut.
4. Cut the fishing line into three pieces of 16" each. Tie one end of one piece of fishing line to a paper clip.
5. Tie the fishing line to the loop end of the eyebolt so that the paper clip is just touching the magnet and the line is tight.
6. Adjust the eyebolt by turning it so that the paper clip is not touching, but so that it appears to “float.”
7. Stick the ruler (on self-adhesive stock) onto the front of the thin wood back piece. The zero mark should be at the very edge on either side; the white edge of the label on either side needs to be cut off. When positioning the ruler, be sure that the ruler markings run perpendicular to the desk top, and that the ruler markings match up with the taut string when observing the string at eye level. This way the numbers will be readable above and below the string.
8. The Magnetic Levitation Device apparatus is now assembled and ready for use. Note: Flinn Scientific believes in conserving resources when at all possible. The wood pieces included in this kit may not be blemish-free since they are scrap pieces from our cabinet-making processes. We did not feel this would affect the functionality or quality of the device in any way.

• Add paper clips very carefully so the force of setting the clips on the wire does not break the field.
• Read the distance scale behind the floating clip accurately.
• Adjust the distance between the floating clip and the magnet using the eyebolt. Students need to be able to get the clip within 1 or 2 mm to start the experiment.
• Make sure students don’t allow the floating clip to touch the magnet during data collection. Sometimes students don’t notice it is touching and no longer floating.
• Bend the mass clips open slightly to allow them to slide easily on and off the fishing line and the first paper clip.

Safety Precautions

Keep the magnetic levitation device away from computer floppy disks and computers. The strong magnet can create errors on computer disks and interfere with electronic equipment. Always follow normal laboratory safety guidelines.

Teacher Tips

• This laboratory kit contains enough materials to assemble three magnetic levitation devices. All materials are reusable. Assembly instructions are provided. It is suggested that the devices be assembled by the teacher prior to laboratory time.
• Students should work in groups of two, three, or four, depending on class size. Two class periods are recommended to complete the experiment. Day 1—Exploration and data collection. Day 2—Data collection and graphing.
• Student exploration time with the levitation device is important. Students are fascinated when the paper clip first starts floating.

Further Extensions

1. Torque Experiments—This magnetic levitation device can also be used to experiment with torque. In a torque experiment, the eyebolt and the magnet act as anchors. The distance between the “floating” clip and the magnet is held constant, and the distance the hanging clips are from the eyebolt is varied. The closer the clips are to the midpoint between the eyebolt and the magnet, the greater the torque they exert. The torque that the clips exert can be calculated using the formula:

Torque = force x distance

The clips always exert the same force, but as the distance from the ends increases, the torque also increases. Start this investigation by asking students to predict: Where will the fishing line hold the LEAST number of clips—the beginning (by the eyehook), the middle, or the end (by the “floating” clip)? Allow students to set up an experiment to test their predictions.

2. Magnetism Experiments
   
   1. Challenge students to find a material that will interfere with the magnetic field if that material is placed between the magnet and the paper clip. Allow students to experiment.
   2. Which is attracted to the neodymium magnet more strongly—a small paper clip or a big paper clip? Allow students to experiment.

Sample Data

Magnetic (and gravitational) forces are inversely proportional to distance, according to the equation F α 1/d². For example, if the clip is twice as close to the magnet, the force is four times stronger. Three times closer, the force is nine times stronger. Four times closer and the force is 16 times stronger!

The force (number of paper clips) it takes to make the fishing line fall can be graphed against the distance the “floating” clip is from the magnet. Student graphs will not be straight lines, but will be curved like a parabola (curve). This is why the Moon exerts so much more gravitational force on the Earth compared to the Sun. The Moon is much closer, and when dealing with forces, distance can be more important than size!

Data Table

Answers to Questions

1. As the paper clip is moved further away from the magnet, the force between the two objects decreases. This is true with magnetism as well as gravity. As the distance increases, the force decreases. This is known as an inverse relationship.
2. If a stronger magnet had been used, the force between the paper clip and the magnet would be greater, but similar behavior would be observed. The shape of the curve generated from the data would be identical, just shifted higher on the force scale. A stronger magnet allows the paper clip to “float” further away without falling. This is similar to the stars and planets. The larger the mass of a star or planet, the more gravitational force it exerts on the planets and objects orbiting it.
3. When the distance between the magnet and clip change from 5 mm to 10 mm (doubles), the force between them drops more than in half. That is because with both gravity and magnetism, force is proportional to the inverse square of the distance. (F∝1/d²). This means if the distance doubles, the force becomes four times less. If the distance triples, the force becomes nine times less.
4. Mass and gravitational attraction are directly related. When the mass doubles, the gravitational attraction doubles. Distance and gravitational attraction are related as the inverse square relation. When the distance is cut in half, or the object becomes two times closer, the gravity is four times greater. Distance affects gravitational and magnetic forces much more than mass.
5. The force of gravity holds the Moon in orbit around the Earth.
6. The Sun has much more mass than the Moon.
7. Tides on the Earth are affected by both the Moon and the Sun; however, the dominant force affecting tides is the Moon. This is because even though the Sun is about 30 million times more massive than the moon, it is about 93 million miles away. The moon is only about 250,000 miles away from the Earth. The Sun is about 400 times further away. Since the distance affects gravity much more than mass, the Moon is the dominant force affecting tides on Earth.
8. The Sun exerts the most gravitational force on Mercury since it is the closest planet to the Sun.
9. Mercury moves through space faster than any other planet. Mercury must move faster than the other planets because there is so much gravitational force being exerted on it from the Sun (since they are so close). If Mercury slowed down, even a little, the gravitational force from the Sun would pull Mercury in and it would crash into the Sun. Mercury moves through space at about 49 km/sec compared to the Earth that moves through space at about 30 km/sec.
10. The Sun exerts the least force on Pluto since Pluto is the furthest planet from the Sun.
11. Of all the planets, Pluto must move the slowest since there is very little gravity “holding” it in orbit around the Sun. The period of revolution for Pluto is 248 Earth years. (One time around the Sun takes 248 years on Earth). Not only does Pluto have further to travel around the Sun, but it also travels the slowest. Pluto travels at a slow speed of about 5 km/sec compared to a speed of about 30 km/sec for Earth.
12. Students can use a computer software program to plot the points on a graph and create a best-fit line and equation. Students can also plot the theoretical points on their original graph using a different color. They should use the equation F = A/d² to determine the force, where A is a proportionality constant that equals the number of paper clips added when the distance between the magnet and the paper clip is 1 mm. The students can then draw the best-fit line through these points and compare it to the data line.

References

Special thanks to Bill Grosser, Glenbard South H. S., Glen Ellyn, IL, for providing Flinn Scientific with this laboratory activity. The magnetic levitation device evolved from an original device first used by Frank Dzikonski, retired science teacher, Arlington Heights School District 25, Arlington Heights, IL.

Introduction

Determine how the distance between two objects affects magnetic and gravitational forces.

Concepts

• Magnetic and gravitational forces
• Astronomy
• tides and planetary orbits
• Torque

Background

Forces hold the universe together. Everything from the galaxies to atoms are held together by the one or more of the four known forces—strong and weak nuclear forces, gravitational force and electromagnetic force. While it is not possible to “see” a force, the effect that forces have on objects can be seen and studied. The magnetic levitation device can be used to simulate the effect that distance has on the gravitational force. The actual force being tested is the magnetic force of a small magnet on a paper clip, but this force behaves in a similar manner to that of the gravitational force between two objects (like the Earth and the Sun). In that capacity, the magnetic force can be used to simulate a gravitational force. Both forces depend on two properties. One is the intrinsic property of the material (i.e., an object’s mass for gravitational force and the magnetic moment of a magnet). The other is the distance between the affected objects.

In this experiment, the effect of distance will be studied. The force that it takes to make a string fall will be measured and graphed against the distance the “floating” clip is from the magnet. This simulates the gravitational force of a planet on a satellite. Since magnetic force and gravitational force behave similarly with distance, this is a good simulation to show the effects of gravity and/or magnetism in relation to distance.

This experiment may help to explain why the Moon affects the tides much more than the Sun, even though the Sun is nearly 30 million times more massive than the Moon!

Materials

Prelab Questions

Read the Procedure that follows. Predict the relationship between force and distance. Draw a rough sketch illustrating your prediction on the small grid.

If using this lab for gravitational studies, use the following questions:

1. What causes the tides on the Earth?
2. Do planets revolve around the Sun together like spokes on a bike wheel, or do some go faster than others?

Safety Precautions

Keep the magnetic levitation device away from computer floppy disks and computers. The strong magnet can create errors on computer disks and interfere with electronic equipment. Always follow normal laboratory safety guidelines.

Procedure

1. On a separate sheet of paper, construct a data table similar to the Sample Data Table shown. Leave space for 10 to 12 different distances. Do not yet fill in any distance or force numbers.
2. Use the eyebolt to adjust the “floating” paper clip so it is as close to the magnet as possible without touching it. Measure the distance in millimeters between the paper clip and the magnet. Record this measurement in the data table as the first, or “minimum,” distance.
3. Carefully hang one paper clip on the fishing line 18 cm away from the loop end of the eyebolt. Hang additional paper clips onto the first paper clip, slightly unbending each one so it can be easily hung. Make sure the first clip remains at the 18-cm point. Count the additional paper clips as they are added onto the first clip. Continue adding paper clips until the magnetic force is broken and the “floating” paper clip falls. (Note: Add the paper clip masses slowly and carefully.)
4. Record the total number of paper clips (the force) needed to make the “floating” clip fall. Do not count the “floating” clip. The mass of the “floating clip” and the mass of the string will be considered constants in the experiment. (Note: This force is the force required at the “minimum” distance.)
5. Determine the maximum possible distance at which the “floating” paper clip will “float” by turning the eyebolt out slowly (with no hanging paper clips on the line). Read the exact distance at which the magnetic force is broken and the “floating” paper clip falls—the distance for the force of zero added paper clips. Record the measurement in the data table as the maximum distance and the minimum force (force of zero).
6. Repeat the experiment for at least 8–10 other distances, choosing distances equally spaced between the maximum and minimum and always hanging the clips at the 18-cm mark. Record the distance (between the “floating” clip and the magnet) versus the force in number of paper clips required to make the “floating” clip fall. Conduct the 8–10 other trials, increasing the distance by turning the eyebolt.
7. Prepare a graph comparing distance and force. The graph should be a plot of distance in millimeters on the x-axis (horizontal axis) and force in “clips” on the y-axis (vertical axis).

1. How does the force between the “floating” paper clip and the magnet change, as the “floating” paper clip is moved away from the magnet?
2. If a stronger magnet had been used, how would the force between the paper clip and the magnet have changed? (Optional: Draw a colored line on your graph showing how the data might have looked with a stronger magnet. Include a key on the graph explaining the two lines.)
3. When the distance between the magnet and “floating” clip changed from 5 mm to 10 mm (doubled), how did the force (number of clips) change? Did it double also, drop in half or drop more than in half? Explain.
4. Which has a greater effect on gravitational force—the mass of objects or the distance between objects?

5. What force holds the Moon in orbit around the Earth?
6. Which has a larger mass—the Moon or the Sun?
7. Tides on the Earth are mainly due to the gravitational force that the moon exerts on the Earth. Why does the Moon affect tides more than the Sun, even though the Sun is so much bigger?
8. On what planet does the Sun exert the most gravitational force?
9. Which planet must move the fastest in order to stay in orbit?
10. On which planet does the Sun exert the least gravitational force?
11. Which planet must move the slowest to keep from flying out of the Solar System?
12. Calculate the equation for the line. How close does your data come to supporting Newton’s Universal Law of Gravitation, F α 1/d²?