Explore the physics of fidget spinners while designing one of your own!
- Moment of inertia
Fidget spinners are largely dependent upon two physics concepts—friction and moment of inertia. Friction is created when any two surfaces are in contact with each other. The factors that influence friction include the surface finish (or smoothness), the cohesive and adhesive ability of molecules, and the force holding the surfaces together. Surface finish is a major contributor to the frictional force. All surfaces, no matter how smooth, have irregularities. Commercial fidget spinners use a ball bearing at the center to minimize any frictional force that would otherwise slow down the spin of the toy.
As you may have noticed, many toy fidget spinners have ball bearings located on each of the arms in addition to the center. These are used to add mass to each arm. All mass has the property of resisting a change in motion, or inertia. An object in motion tends to stay in motion, and an object at rest tends to stay at rest. For rotational motion (spinning motion), the motion “resistance” is a property based on the mass and the spatial distribution of the mass around a point of rotation (or axis of rotation). This specialized case of inertia is called moment of inertia. The distribution of the mass affects the moment of inertia in such a way that the further the bulk of the mass is distributed from the point of rotation, the larger the moment of inertia will be, and therefore, the harder it will be to change the object’s motion. The mass added to the arms of the toy spinner reinforce this concept. Once the spinner has been put into motion, the mass on the arms makes it harder for the toy to change motion. In other words, the mass helps keep the arms spinning in the original direction. If, instead, the mass were moved closer to the center of the spinner, the toy would likely not spin as long.
The purpose of the Introductory Activity is to demonstrate the concept of moment of inertia by building a simple model. Next in the Design Challenge, you will design a fidget spinner using everyday materials. Who can design the longest spinning toy?
Timer or stopwatch
Washers, various sizes
- Read the Introductory Activity procedure.
- You are instructed to enlarge the hole in the cardstock to be slightly larger than the diameter of the skewer. Why might this be necessary?
- Make a prediction as to which arrangement of paper clips will result in the longest spin.
The tip of the wooden skewer is very sharp. Blunt the tip with sandpaper. Wear safety glasses. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.
Part A. Introductory Activity
Part B. Design Challenge
- Using scissors, cut out one 12 cm x 4 cm strip of cardstock.
- Find the center of the strip using a ruler and mark it with a pencil.
- Use the end of a paperclip to poke a hole through the marked spot.
- Enlarge the hole by threading a bamboo skewer through, sharp end first. The hole should be slightly larger than the skewer.
- Holding the end of the skewer in one hand, use your other hand to flick the strip of paper so it spins around the skewer. Repeat a few times until it moves consistently.
- Next, spin the strip of paper while your partner records the spin time using a timer. Start the timer as soon as the strip is flicked, and stop when the paper comes to a complete stop. Repeat two times, and record the spin durations in the following data table.
- Attach two paperclips to the strip of paper on each side of the bamboo skewer. Place the paperclips so they are as close to the skewer as possible without touching.
- Spin and record the spin duration in the data table.
- Slide the paperclips to each end of the strip. Spin and record the spin duration in the data table for three trials.
- Use the remaining space in the data table to experiment with placement and number of paperclips for various trials. Record the duration of each spin, average spin times and any observations.
FlinnToy Company is interested in manufacturing and selling a new fidget spinner toy. You have been chosen by FlinnToy to submit a design prototype for a fun, easy-to-use fidget spinner. FlinnToy will choose the longest spinning fidget spinner. The total cost budget for the final manufactured toy is $5.00.
- Record the materials used in the design process in Data Table 1 on the Fidget Spinner Design Worksheet. The cost of materials are listed below. Any material taken from the supply area should be accounted for. Do not account for any tape or glue used in direct material costs.
- You must purchase each item as a whole. For instance, you cannot pay for only half of a sheet of paper—anything that is unused will count toward waste cost.
- Record the required materials and costs for the final manufactured product in Data Table 2.
- You will be given a designated amount of time to design and build the toy fidget spinner. Testing and making modifications must be made during that time period.
- When time is up, test your design with a partner. Record your results in Data Table 3.
Basic Fidget Spinner Design
- Cut out the design of your choice from the Fidget Spinner Design Template.
- Choose a fidget spinner body from the provided materials. Trace the design onto the chosen materials, and cut it out using scissors.
- Use a paperclip to poke a hole in the center of the spinner.
- Widen the hole using the sharp end of a bamboo skewer. The hole should be slightly larger than the diameter of the skewer.
- Using scissors, carefully score and break a 1.5-cm piece of bamboo skewer to use as the spinner bearing.
- Use sandpaper to smooth the cut ends of the bamboo skewer.
- Insert the piece of skewer through the hole in your spinner.
- Hold the skewer between your thumb and index finger so the spinner is vertical. Use your other hand to flick the spinner.
- Weights may be affixed to the arms of the spinner using tape or glue.
- Two circular pieces of cardboard or foam can be placed on each side of the spinner body to prevent the body from moving while in motion; these can also be considered “finger grips” (see Figure 1).