Welcome to the SchoolhouseTeachers.com. Tinkers* Club. May 2014: Pop a balloon with a magnet

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1 Welcome to the SchoolhouseTeachers.com Tinkers* Club When curiosity is raised, learning occurs. Ed Sobey, Ph.D. President, Northwest Invention Center : Pop a balloon with a magnet Can you pop a balloon with a magnet? If you have your own idea of how to do this, go for it. If not, get some stuff together and follow along. Let s build a machine that will pop balloons. Why? Because it s fun! We ll make an electromagnet and use this as a motor to poke a pointy pike at an inflated balloon. If you have a camera, you can try to record what happens. To make an electromagnet, you need some magnet wire. Electronic stores carry this, or you can order online. Wrap the wire around a sturdy straw that is about 2 long. However, before you start wrapping, find a nail that fits into the straw. The nail should slide easily inside the straw. Keep 2 or 3 of each end of the wire free, away from the straw. You ll connect these ends to a battery later. Wrap magnet wire around a sturdy straw. Make at least 200 windings, but first keep the leading end free of the wrappings so you can connect it later to a battery. Now, start winding and wrapping. Keep going. The more windings you make, the better the electromagnet will be. Try to achieve 200 windings. Wind the wire up and down, around and around, but keep it within about 2 on the length of the straw. Magnetic wire has a coating on it so that it doesn t conduct electricity from one layer of windings to the next. To connect the wire, you need to sand or use steel wood to scrape off the coating from about 1 of each end.

2 2 I glued the electromagnet to a wooden paint stir stick (free at hardware stores). Both ends of the wire have had the insulation scraped off with steel wool so connections can be made to a battery. When you have way more windings on the straw than your hands wanted to put there, scrape the coating off each end and connect the two ends to a 9-volt battery. The windings are now an electromagnet. See how many steel paperclips the magnet will pick up. The more current and the more windings you have, the stronger the electromagnet will be. Only use batteries to power your electromagnet. Don t connect it to a wall outlet. Make a motor With one small addition, you can make a motor out of the electromagnet. Insert a nail into the straw so that about half of the nail sticks out of the straw. Connect the ends of the coil to the battery and watch what happens. When you energize the coil, the nail is drawn in. Try this again with the wires reversed. The wire that was connected to the positive terminal of the battery (see the + sign on the battery) should now be connected to the other terminal. The wire that was on the negative (-) terminal now goes on the positive terminal. You get the same result. The nail is drawn into the straw. If your house has door chimes, it probably is a device like this. When the doorbell button is pushed, electricity flows through a coil and moves a plunger to hit a chime. A spring pulls the plunger back as soon as the electrical current stops. Instead of a spring, you can use gravity to return the plunger to its starting position. How do you get the plunger to jump out of the coil instead of into the coil? Put a magnet on the head of the nail. Now the electromagnet will oppose the magnetic field of the permanent magnet and launch the nail upward. If this doesn t happen when

3 3 you first try it, flip the magnet upside down or reverse the connections to the battery. Connect the + side of the battery to the wire that was on the negative side and vice versa. The magnet on the head of the nail pulls the nail up and out of the straw when electricity flows through the coil. When the battery is disconnected, the nail and magnet fall back down into the straw. Attach something that will make a nice sound when it is hit and you ve made a chime. A glass will work, but make sure you have permission of the owner of the glass. You don t want to have to apologize if the glass breaks. If you attach something sharp to the magnet, the upward thrust of the plunger can pop a balloon. A sewing needle will work, but a paper clip may be easier. File the end into a sharp point and bend it perpendicular to the rest of the paper clip. The magnet will hold the paper clip in position without glue or tape. I ve sharpened the end of the paper clip with sanding paper. The clip is held by the magnet, ready to puncture a balloon.

4 4 Inflate a balloon and tape it into position so the sharpened paper clip will hit it. Give the balloon popper a try. You can improve the balloon popper by using a switch to turn on the electromagnet. Hobby and electronic stores carry lots of switches. Get an inexpensive switch that will be easy to connect to the two wires. What was that? What happens when a balloon pops? Do you have a digital camera that can record images quickly? Try filming the popping of a balloon. Look at these images. These were shot 1/30 th of a second apart. The first shows the balloon intact. The last shows the balloon has burst. As fast as the camera was, the bursting of the balloon occurred during one frame. Look at the middle image. In the instant the image was being collected on the chip inside the camera, the balloon changed from inflated to burst. Here is the balloon immediately before being popped. Figure 11/30th of a second after the previous photo was taken the balloon pops. You can see the balloon, but its image is much weaker than in the previous photo. The inflated balloon existed for only part of the time this image was taken.

5 5 The next image taken, again 1/30th of a second after the previous image, shows a piece of the balloon flying off to the right and the blue tape (that held the balloon in place) being blown off to the left. Shot at 100 frames per second, this image captures the moment the balloon has burst. The image shows both the inflated balloon and the popped balloon. The time needed to capture the image is much longer than the time taken for the balloon to pop, so it is a combination of the two. You can see the outline of the balloon faintly. The camera saw the intact balloon for a fraction of the time the middle image was exposed. The rest of the time the camera was collecting light during that shot, the balloon had blown apart. The burst occurred much faster than 1/30 th of a second. Filming it three times faster still isn t fast enough to see one image with the balloon intact and the next image with it gone. To capture that event the camera would have to operate 20 times faster. Here is my balloon popper made out of a shoe box. When I connect the battery to the circuit, the nail and magnet with paper clip will jump up and hit the balloon (not shown here).

6 Papa Flash 6 To see things that were happening extremely fast, Harold Edgerton built strobes. Strobes are lights that turn on and off very quickly. Keeping the camera lens open and turning the lights on and off quickly allows rapidly changing images to be captured. Check out the collection of Doc Edgerton s amazing photos in the book, Stopping Time The Photographs of Harold Edgerton. Libraries have or can borrow this book for you.