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INTERACTIVE LECTURE DEMONSTRATION PROCEDURE

This is a modification of the procedure for use with shorter more qualitative demonstrations.

1. Describe the demonstration. If it involves taking measurements do the demonstration without showing results.

2. Ask students to think about what will happen. You may want to have them put predictions on printed form. You may want to ask several questions. If using clickers find out what students are predicting.

3. If time allows have students engage in small group discussions.

4. Check again using clickers to see if anyone is changing their prediction

5. If using paper forms have them record final prediction.

6. Carry out demonstration including any measurements.

7. Have students record results if using  paper form.

8. Discuss the results. Answer questions.

EXAMPLE DEMONSTRATIONS (#'s refer to description on web site) 

1. OPTICS #6A60.30 Produce an image of an arrow using a convex lens. Ask about the orientation of the image and what happens if  you cover up half of the lens.

2. MECHANICS #1F30.10 Use air track to have a cart collide with a cart of equal mass at rest. What will happen? Which conservation laws are involved?

3. ELECTRICITY AND MAGNETISM #5F30.10 Connect battery, switch, large capacitor, and flashlight bulb in series. What happens to brightness of bulb when switch closed? Then discharge capacitor through bulb with battery bypassed. Deluxe version: Add meters to show voltages and current.

4. ELECTRICITY AND MAGNETISM #5F20.50 Compare brightness of single bulb with bulbs in series and parallel. Deluxe version: Add meters to show voltages and current.

5. MECHANICS #1Q20.10 (Newer Version) We have a device to demonstrate conversion of gravitational potential energy to rotational kinetic energy. What happens if vary position of masses on the rods?

6. MECHANICS #1N30.10 Newton's Cradle device. What happens if release one ball, two balls? For a surprise see what happens if use balls on the curved wooden device.

7. ELECTRICITY AND MAGNETISM #5K20.25 Eddy currents. Drop lead weight down tube and time. Then drop small magnet. Extra:Try with plastic tube rather than metal.

8. FLUIDS #2C20.30 (New Version) Bernoulli #1 Suspend a balloon over air stream from hair dryer. What happens when tilt the air dryer while keeping it pointed at balloon?

9. FLUIDS #2C20.45 Bernoulli #2 Suspend two bowling balls from a rod so they are about 1" apart. What happens when blow air from leaf blower between bowling balls?

10. THERMODYNAMICS  #4B30.23 Put ice cubes on two blocks that look alike but are made of different materials. Is there a difference in rate at which ice cubes melt? Talk about conductivity and specific heat.

11. THERMODYNAMICS If you put ice cubes in tap water and salt water, which ice cubes will melt faster? The answer involves convection currents and density differences. Deluxe version: use ice cubes with food coloring added to show effect of convection.

12. ELECTRICITY AND MAGNETISM #5A10.10, 5A20.10, 5A40.20 Show effect of charged rod on charged objects and on leaves of electroscope. Then see what happens if you use an insulator like a meter stick suspended from a string or a board balanced on a watchglass.

13. ELECTRICITY AND MAGNETISM See what happens if bring a magnet near various materials. Then see what happens if bring strong magnet near a dollar bill. 

14. FLUIDS #2B20.40 Pascal's "Vases"(New Version). Add food coloring to water. Before adding water to apparatus ask which tube will have the highest water level. Thought Experiment: Consider three containers with same base area. One has sides tilted so area at top is smaller than base. Second has vertical sides. Third has sides tilted outward so top has larger area. Containers are built so weight same. What happens if they are put on scales and water added to same height? For answer go to:       http://www.fas.harvard.edu/~scdiroff/lds/NewtonianMechanics/PascalsParadox/PascalsParadox.html

15.MECHANICS #1N30.50 Hit the block of wood using the sharp pointed swinging device to demonstrate inelastic collision, Remove sharp point. Ask what will happen when rubber ball hits wooden block (%7e elastic collision). The block will fall over because the momentum transfer is greater even though mass is reduced by removing metal tip.

16. FLUIDS #2B40.54 Classic Coke or Pepsi versus Diet Coke or Pepsi. Predict what happens when container of each is placed in water. What factors determine if something floats or sinks? Classic drink will sink (corn syrup versus Nutra Sweet). 

17. ELECTRICITY AND MAGNETISM Instead of using a battery to charge up a capacitor use the Genecon device. After charging up the capacitor ask which way the handle will rotate when you turn it loose.

18. MECHANICS #1H10.20 Use the fan cart with and without sail. Which way will it move? Put on long air track to remove friction.

19.MECHANICS #1F20.10 Which string breaks first in the two suspended weights and string demonstration?

20. MECHANICS #1Q10.30 Which gets to the bottom first if roll hoop and solid disk down incline?

21. THERMODYNAMICS #4A30.20 If you heat a metal ring does the inside diameter increase, decrease,  remain same or depend on type of metal?

22. FLUIDS Put a ball that floats in water colored with food coloring. Pour in a second liquid that does not mix with water and is lower density so it floats on water. What happens to ball: Rise higher, sink lower, stay at same level compared to water level?

New Questions Added July 2012

  1. What happens to brightness of a flashlight bulb in series with a battery if the bulb is bypassed by a piece of wire? For questions 1-5 construct the circuits to demonstrate what happens.
  2. What happens to brightness of A if switch closed?  A and B are in series with battery. Switch causes B to be bypassed like bulb in question above.
  3. Which would be brighter? Two bulbs in parallel or two in series if voltage same?
  4. Two batteries are in series. The batteries are is series with two bulbs. A switch (open) connects middle of two batteries with middle of two bulbs. What happens to brightness of bulbs if switch is closed?
  5. Which weighs more? Ignore complications due to temperature differences. A) full glass B) full glass with ice cubes or ping pong balls  floating in it  C) same weight   Weigh on pan balance.
  6. Put four 100g masses in a plastic cup.  Prepare an identical cup with one mass inside and three taped to the bottom. Fill a clear container partly with water and mark level with tape (orange or blue    1. Put cup with masses inside in large clear container. Use a piece of tape to mark water level.   2. Ask what will happen to water level (relative to the container) if three of the masses are taken out of the cup and put in the water. One mass is left in cup for stability.  Do this and mark water level. Comment on water level. 3. Take the cup and masses out of the water. If needed add water to bring water back to initial level. Ask what happens to water level if put cup with masses taped on bottom into water? Do this and comment on water level.  In case 2 water level drops compared to case 1. In case 3 the water level is the same as case 1.   If you have extra time ask about how high cup floats out of water in each case.  For example: A barge loaded with a stack of steel plates is approaching a low bridge. Would the clearance be helped or hindered by tossing a plate or two overboard?  The experimental result is hindered. Whether It's a river/canal or a closed swimming pool/lake, It doesn’t matter. If you are talking about standard masses in a plastic cup or perhaps dumping metal plates from a large ship in a Panama Canal lock the water level will go down. If you are talking about a boat in a lake or river the change in level will generally be too small to matter. However the boat, cup or ship will rise relative to the water. You can demonstrate that this is a bigger effect than dropping of water level for standard masses in a cup or attached to a small boat. Dropping the masses in the water would make the clearance situation worse. To lower a boat trying to go under a bridge it would help to add weight.
  7. Try #6 using wood or other material with density < water.


Last Updated: 07/06/2016