Conceptual Physics Class Demos

    We share these for use by Qualified Science Educators Only. Some have inherent safety problems that must be provided for. We have room for the demonstration outline only. You must assume the responsibility for the safety and success of your own demonstration.

Week 1

Science seeks to understand the world around us:

  • Take students outside.
  • Ask students to carefully observe their surroundings for three minutes. After the three minutes, ask detailed questions about the surroundings. Examples: How many trees can be seen; How many windows are on the building; How many people have walked by; How many cars have passed; etc. Discuss the importance of observation in science.
  • Ask questions about the physical surroundings. Examples: How is the concrete (asphalt) in the parking lot made; Where does the electricity in the electric line come from; What kind of cloud is that; How do clouds form; etc. Discuss the inquisitive nature of scientists.
  • Ask students what questions they have about their surroundings.
Lab safety: danger
  • Place a small piece of sodium metal in a beaker of water.
  • Na + H2O NaOH + H2
  • The exothermic reaction usually causes enough heat to ignite the hydrogen gas explosively.
  • If this reaction was not anticipated, it could cause serious injury.

Week 2

Measurement standards:

  • Ask - Which is bigger, a yard or a meter?
  • Ask - How do you know? Continue until someone mentions a meter stick and a yard stick.
  • Show both a meter stick and a yard stick.
  • Ask - How do you know these are the right length? Continue the line of standards until the "ultimate" standard is reached. There must be some unchanging standard that is available to everyone.
Density #1:
  • Before class - put corn syrup, glycerine, and water into a cylinder.
  • It will appear, at a glance, to be one liquid.
  • For the demonstration, add a steel ball, a rubber stopper, a plastic pen cap, and a piece of wood.
  • Compare the density of these materials.
Density #2:
  • Show a piece of paper, a rock, a piece of wood, and a piece of metal.
  • Will these objects float in water?
  • How do boats made of wood and steel float?

Week 3

All matter takes up space:

  • Fit a funnel into the neck of a bottle.
  • Seal the funnel in place with modeling clay around the neck of the bottle.
  • Quickly fill the funnel with water.
  • Observe
Inertia #1:
  • Suspend two 1Kg weights by thread from a horizontal bar.
  • Tie loops of the same thread to the bottom of the weights.
  • Which string will break when the bottom loop is pulled?
  • With a steady pull, the top string will break because of an increase in the hung weight.
  • With a quick jerk, the bottom string will break because of the inertia of the weight.
Inertia #2:
  • Completely fill a pop bottle with water.
  • Invert this bottle over an empty bottle using an index card.
  • Remove the index card - Quickly.

Week 4

Phase change: caution

  • Boil some water in a beaker.
  • What are the bubbles?
  • What causes the bubbles to form?
Making crystals:
  • Use two tall glass containers - half fill one with sugar and the other with salt.
  • Pour hot water into both containers almost to the top. Stir to dissolve the solids.
  • If all the solid dissolves, add more solid. There should be a small amount of undissolved solid in the bottom of the container. This assures that the solutions are "saturated".
  • Prepare two clean, white strings with a weight (washer or paper clip) tied to one end.
  • Roll each string around a pencil. Adjust the length of the string so the weight almost touches the bottom of the container.
  • Lay a pencil across each container and adjust the length of the strings so they do not touch the bottom.
  • Set the containers aside uncovered in a warm place where they won't be disturbed for several days.
  • If a crust forms on the surface of the liquid, carefully break up the crust so the water can evaporate. As the water evaporates, more crystals will grow on the string.
  • After the crystals stop growing, remove the strings and allow the crystals to dry in air.
  • Closely examine the crystals. Do sugar and salt form crystals that are the same shape?
The gas laws:
  • Use a flask that a balloon will just fit over its mouth.
  • Place a small amount of water in the flask and just bring it to a boil.
  • Quickly stretch the balloon over the mouth of the flask.
  • Continue heating the flask to make the balloon grow.
  • Remove the flask from the heat and let it cool.
  • The balloon will be pushed into the flask by air pressure.

Week 5

Solutions:

  • Put a small spoonful of sand into a beaker.
  • Put an equal amount of salt into another beaker.
  • Add water to both beakers to make them about half full.
  • Stir both beakers.
  • Which of these is a solution? Why?
Colloids:
  • Dissolve 10g of calcium hydroxide in a small amount of water (just enough to dissolve the solid).
  • Mix alum into the solution.
  • The colloid aluminum hydroxide gel should begin to form.

Week 6

What alchemists tried to do: caution

  • Place about 5 g of Zn dust in an evaporating dish.
  • Fill the dish one-third full of NaOH.
  • Heat to near boiling.
  • Clean a penny with steel wool and place in the dish.
  • Heat 3-4 minutes until reaction is complete.
  • Wash the penny under running water and gently blot dry. The penny looks silver - it is zinc coated.
  • Hold the penny in a burner flame (use tongs) long enough for the color to change. The penny looks Gold - it is brass coated.
  • Brass is 60 to 82 % Cu and 18 to 40 % Zn.

Week 7

Atoms are mostly empty space:

  • Begin with - "You already know that atoms are made of a small nucleus, containing protons and neutrons, with electrons circling the nucleus. How can atoms, that are mostly empty space, make up solid matter?"
  • After discussing student answers, use an electric fan to demonstrate the concept.
  • Tell students the story of the development of machineguns on World War 1 airplanes and how they were made to shoot between the propeller blades.
  • Ask: could this be applied to atoms?
  • Discuss
Describing matter by indirect observations:
    Since atoms and the particles that they are composed of are too small to see, we must rely on indirect observations to learn about them. This demonstration shows how limited this process is.

  • Cover the bottom of a shallow tray or pan with a thin layer of flour or sand.
  • Make an imprint of an object in the flour or sand without students seeing the object.
  • Have students identify the object that made the imprint.
Space between particles of matter:
  • Fill a glass with marbles. Is the glass full?
  • Pour sand into the glass until full. Is the glass full?
  • Pour water into the glass until full. Is the glass full?
  • Pour salt, slowly, into the glass.

Week 8

How big is an atom?

  • Place 12 g (one mole) of carbon (powdered charcaol) in a beaker.
  • How many atoms of Carbon are in this beaker?
  • With every person on earth counting one of these atoms a second, it would take about 5 million years to count them all.
Moving atoms from place to place:
  • Put 10 or 15 dull pennies in a beaker.
  • Half fill the beaker with vinegar.
  • Put a spoon of salt in the beaker and stir the contents of the beaker.
  • Observe the pennies. Discuss why the pennies become bright.
  • Carefully pour the liquid into another beaker.
  • Observe the liquid. Discuss the color of the liquid.
  • Use steel wool to clean an iron nail until it is bright.
  • Place the nail in the liquid. After 15 minutes, observe the nail and the solution.
  • Discuss the observations.

Week 9

Chemical activity of group 1: danger

  • Show small pieces of lithium and sodium metal.
  • Point out that they are in the same family on the periodic table. Ask what that tells you about the two metals.
  • After students have answered, place the metals in two separate containers of water?
  • Do the observations confirm your answer?
  • Ask: What would happen of a piece if potassium metal were exposed to water?

Week 10

Chemical activity of group 2: danger

  • Show that magnesium metal does not react with water.
  • Hold a strip of magnesium ribbon in a burner flame with tongs.
  • Produces a very hot, bright flame.

Week 11

Periodic table:

  • Show an old periodic pable.
  • Show today's pable.
  • Why was the shape changed?
  • Discuss the shape of today's table related to quantum numbers.

Week 12

Activation energy: danger

  • Place equal, small, amounts of potassium chlorate and table sugar in an evaporating dish. There is no reaction.
  • Add one (1) drop of concentrated sulfuric acid.
  • The reaction will produce flames, splattering, and smoke. It should be done in a fume hood or outside.

Week 13

Chemical reaction (color change):

  • Place equal amounts of lead nitrate and potassium iodide in a flask.
  • Did a reaction take place?
  • Stopper the flask and shake.
  • Did a reaction take place?
  • Shaking causes the two white solids to produce a yellow one.

Chemical reaction (precipitate):

  • Place a spoon full of epsom salt (magnesium sulfate) in a beaker of water. Stir to dissolve.
  • Pour liquid ammonia into the beaker.
  • The white precipitate is magnesium hydroxide (milk of magnesia), the insoluble product of the chemical reaction.
  • The soluble product, ammonium sulfate, can be recovered by evaporating the clear liquid from the beaker.

Week 14

Balance this chemical reaction:caution

  • Set up two gas generating bottles.
    • One to generate hydrogen:
      • Almost cover the bottom of the bottle with zinc metal
      • Half fill the bottle with dilute HCl.
      • Quickly stopper the bottle.
    • One to generate oxygen:
      • Put 100 ml of bleach in the flask.
      • Add about 5 g of cobalt (II) chloride.
      • Quickly stopper the bottle and swirl the contents.
  • Using an ignition tube, collect about 2/3 of the tube full of hydrogen, then finish filling the tube with oxygen.
  • Carefully ignite the mixture of gases with a burning splint. This will produce a loud BANG.
  • Have students notice that water has formed inside the tube.
  • Write a balanced equation for the reaction.
Optional:
Collect bottles with different amounts of each gas. Ask students which combination was the best.


Week 15

Endothermic reaction: caution

  • Put a small puddle of water on a block of wood.
  • Place 20 g barium hydroxide and 10 g ammonium thiocyanate in a 50 ml beaker.
  • Set the beaker in the water and stir the contents of the beaker.
  • The beaker will freeze to the board.

First-aid cold packs demonstrate spontaneous endothermic reactions.
Break the water pouch and mix contents.

NH4NO3 (s) + H2O (l) NH4+(aq) + NO3-(aq)

H = +26.2 kJ/mole = +326 J/g

Exothermic reation:

  • Before class, heat an amount of copper (II) sulfate pentahydrate to drive off the water - it turns white.
  • For the demonstration, add a small amount of water to the white powder.
  • Feel the beaker get hot.

First-aid hot packs demonstrate spontaneous exothermic reactions.
Break the water pouch and mix contents.

CaCl2 (s) + H2O (l) Ca2+(aq) + 2Cl- (aq)

H = -82 kJ/mole = -747 J/g

Reaction Rate and Surface Area: caution

  • Place a small pile of flour on a metal tray and try to ignite it with a bunsen burner.
  • Fill a dropper pipet with the flour and shoot it across the top of the burner flame.


Week 16

Suspension and colloid:

  • Place 10 ml of vegetable oil and 10 ml of vinegar in a flask or plastic bag. Do they mix?
  • Shake the flask and observe. This is a suspension.
  • Add one egg yolk and shake. This is a colloid.
  • You might put it on a sandwich. What is it called?
Surface tension:
  • Float some coarse-ground black pepper on water.
  • Ask students why the pepper floats. Density is the most common answer.
  • Add a few drops of alcohol to the water and the pepper sinks.

Week 17

Acid/Base indicator (paper):

  • Astrobrights(tm) Galaxy Gold, a goldenrod colored printing paper.
  • A base turns it red.
  • An acid turns it yellow.
  • Paint a picture or message on the paper with vinegar and let it dry. The picture is now invisible.
  • Spray the paper with a baking soda solution and the paper will turn red everywhere except where the vinegar is.
Acid/Base indicator (liquid):
  • Chop red cabbage up finely.
  • Add the red cabbage carefully to boiling water for 5 to 10 minutes.
  • Let it stand for 30 minutes until it is completely cool.
  • Strain the liquid and throw away the used cabbage. The liquid should be a dark reddish purple color.
  • The color will change when you add acids or bases.
    • Red in a strong acid.
    • Blue in a neutral solution.
    • Yellow in a strong base.

The weak organic acids and bases used as indicators are also found in many other foods:

  • Beet juice changes from red in acid to purple in base.
  • Cherries turn from pink in acid to gray in base.
  • Blueberries turn from purple in acid to green in base.
  • Tea turns from orange in acid to brown in base
What does an antacid do?
  • Determine the pH of a small amount of dilute hydrochloric acid using pH paper (not litmus paper).
  • Dissolve an antacid tablet in the acid.
  • Check the pH again.
  • You might compare different brands.

Other Chemistry Resources:
Science Teachers Lounge

Physics Demonstrations from:
Science Hobbyist | University of Virginia | University of California | University of Texas
North Carolina State University | University of Washington | Sourcebook for Teachers of Physics


Second Semester Demonstrations