PHYSICS MYSTERIES

Physics Mystery #1. New device for discussing momentum conservation in collisions. If sharp point hits board it will wobble but not fall over. If the sharp point is removed so rubber ball hits board it is knocked over easily. Why does it fall over even though moving object has less mass hence less momentum?

Physics Mystery #2 DC CIRCUITS (5F20.55) Put a light bulb in series with 2 bulbs in parallel. Predict what you think will happen. Try to explain what actually happens. Use to talk about series and parallel circuits and temperature effect on resistance.

Physics Mystery #3. Two bar magnets that arrived in the same box show north attracting north and south attracting south. Isn't the rule unlike attract and like repel for both charges and poles? Talk about the double standard for labeling poles N or S. Are you a geologist or physicist?

Physics Mystery #4 Shine a laser along the axis of a cylinder filled with corn syrup. Put a piece of polaroid between laser and cylinder. At one orientation of polarizer the part of the beam farthest from laser will appear very dim. At another orientation the part of the beam nearest the laser will appear very dim. The answer to what is happening involves polarization, optical activity and scattering.

Physics Mystery #5. How can a strong magnet pick up paper? Try using some US currency. There is enough iron in the ink for some of the stronger magnets in the Demo Room to lift the paper.

Physics Mystery #6 How can a hose blowing air out suspend a ball in the air even when tilted at a 45 deg angle? What provides the upward force to overcome gravity? Bernoulli Knows.

Physics Mystery #7 Reverse Magic Instead of making something dissappear you make something appear. Show audience cylinder is empty. Show illuminated platform is empty. Put cylinder on platform. A small car appears inside. Actually the holographic image appears if the cylinder is illuminated with sodium lamp. Determine which end of cylinder is which before trying. No image if cylinder upside down. Could do this deliberately as comical touch.

Physics Mystery #8 Colliding balls revisited. Place 2 identical spheres on one side of small spherical magnet at bottom of curved path. Roll another non-magnetized sphere down hill so it hits spherical magnet Although one ball will come off on the other side as expected it will be moving surprisingly fast. Are momentum and energy not conserved? You might expect ball to move slightly slower due to kinetic energy being tranformed into other forms of energy.

Physics Mystery #9. Magnetic Grapes? Put a grape on the ends of a drinking straw. Balance it on the end of a needle. If you bring an electrically charged rod near a grape it will be attracted. If you bring a strong magnet near the grape it will be repelled. Use to demonstrate diamagnetism.

Physics Mystery #10. Put ice cubes on two near identical blocks. One will melt much faster. Talk about Q=mc(delta T), Q=mL, and conductivity. One block is aluminum painted black to look like other material. Other material has low heat conductivity.

A NEW PHYSICS MYSTERY A circuit consisting of two resistors (different values) and two pieces of wire is placed around a coil like the one used for jumping ring. A voltmeter is connected to the midpoint of the two wires and placed on the left. A second voltmeter is also connected to the midpoint of the wires and placed on the right. The coil is connected to an ac power source. The two meters will show very different voltages. This raises questions about the concept of potential/potential energy in an electrical circuit. It also raises a practical problem if you are measuring voltage where induced EMFs are present. This circuit can also be used as a simulation of quantum superposition. It acts like it is two circuits at once. It could also be used as example of symmetry breaking or parity non-conservation.

AN OLD PHYSICS MYSTERY Although it has been around at least a hundred years Feynmann brought new attention to the question of which way a water sprinkler will spin if the direction of water flow is reversed. There are three groups of theories and results. Some experiments show no result except some jerky movement when water is turned on and off. Some experiments show a slow movement in reverse direction. Some analyses predict a rotation in same direction. Which way do you think it will move?