frictionless_CD

Frictionless CD Puck

Slip sliding away, forever

balloon powered frictionless airpuck
A balloon powered compact disk frictionless airpuck

Introduction

A frictionless airpuck can be built from a compact disk. It will glide across a smooth table top with almost no friction on a cushion of air escaping from a balloon.

Material

A compact disk, CD, music or CD-ROM disks both work.
A hot melt glue gun
A film can lid
a drill with a 1/16 inch bit.
The mouthpiece to a sport water bottle. The kind that pull to open and push to close.
A balloon
A toilet paper tube
scissors
A smooth table top

Assembly

Drill a 1/16 inch diameter hole in the center of the lid of the film can.

Important: Glue the film can to the shiny side of the CD. Put the label side of the CD down toward the table. Small ridges on the shiny side will impair the flight of the CD. Hot melt glue the film can over the hole in the CD with the smooth side of the film can lid up. That is facing away from the CD.

Hot melt glue the water bottle mouthpiece to the top of the film can lid.

water bottle mouthpiece glued to filmcanlid to CD

Hot melt glue the film can lid to the CD then the sport bottle mouthpiece to the film can lid.

completed airpuck

Final assembly.

Blow up the balloon. Twist the neck of the balloon to keep the air from escaping and stretch the neck over the water bottle mouthpiece. Make sure the water bottle mouthpiece is closed.

Cut a length of toilet paper tube long enough so that it will push against the bottom of the balloon and keep it from flopping over. Cut a slit along the length of this tube and slip it between the balloon and the CD. (For my pucks the tubes are about 2/3 the total length of the toilet paper tube.)

The balloon supported by its paper collar.

To Do and Notice

Place the frictionless airpuck onto the top of a smooth table.

Open the mouthpiece.

Push on the airpuck and notice how it slides easily from one place to another.

Notice how it keeps going and going and going.

Tilt the table. Notice how the airpuck slides downhill.

Slide the airpuck upward and to the side on the tilted table. Notice how it follows a parabolic trajectory.

What's Going On?

The air inside the balloon is under pressure. It flows out of the hole in the film can and makes a thin layer between the CD and the table.

The CD slides on this layer of air with almost no friction.

Extensions

Investigate how the diameter of the hole drilled in the film can lid affects the flight of the airpuck. Find hole sizes to give the longest flight time, the fastest speed, the longest distance traveled from one push. Add a side vent to make a rocket propelled air car.

Place magnets on two CD airpucks with all of the magnetic north poles facing up. Push the pucks gently toward each other. They will bounce away from each other, "colliding" without touching.

So What

There are commercial air bearings which can be used to allow one person to push heavy equipment across a smooth floor,

Etc.

This activity evolved from an older activity using records. Black vinyl disks with spiral grooves cut in both sides.

Optional construction

You can replace the water bottle cap and film can lid with a 2-Liter bottle cap. Drill a 1/16 inch diameter hole in the bottle cap and then hot melt glue the bottle cap to the CD.

References