فیزیک و دانستنی ها - دمو های از فیزیک
تاريخ : پنجشنبه پانزدهم بهمن 1388 | 14:23 | نویسنده : اشکان

16.Action & Reaction — Water Rocket


The rocket is filled one third full of water and the remaining volume with compressed air. Velocities in excess of 30 m/s and heights of over 50 meters can be achieved.

17. Velocity of a Baseball

Velocity of a Baseball

A cardboard box is filled with crumpled newspaper so that a thrown baseball makes an inelastic collision with the box. By measuring the recoil distance it slides, the frictional force of sliding, and the mass of the box, the impact velocity can be calculated.

18. Torque bar

Torque bar

A 1 kg weight can be placed at various distances from the axis of rotation. The student is challenged to bring the bar to a horizontal level.

19. Mechanical to Heat Energy

Sphere Energy

Two 1-pound, 2-inch diameter, chrome steel spheres are smashed together with a piece of paper in between. After the collision, a charred hole that smells like smoke, remains in the paper.


1. Air Mass

Air Mass

Fill two balloons with air and attach them to the ends of a meter stick. Balance the meter stick on a narrow edge. Use a pin to release the air from one of the balloons. The meter stick should now tilt toward the balloon that is still filled with air. Ask students to explain why.

2. Hero's Fountain

Hero's Fountain

Two two-liter bottles are connected with a clear plastic tubing running between them. The column of water is balanced against a column of air and water. The water seems to rise higher than the surface of its reservoir.

3. Atmospheric Pressure I

Atmospheric Pressure

Vaporize a few drops of water in a beverage can using a hotplate. With tongs, quickly invert the can and plunge it into a large beaker filled with cool water. The loss of internal pressure, due to the rapid condensation of the water vapor, will allow atmospheric pressure to implode the beverage can.

4. Atmospheric Pressure II

Atmospheric Pressure

A one gallon can is evacuated with a pump and is subsequently crushed by the atmospheric pressure. Alternatively, the can can be crushed by vaporizing a small amount of water and capping the can. Upon cooling, the vapor returns to liquid and loses pressure.

5. Flask Fun

Atmospheric Pressure Volume, temperature

A large flask with a few drops worth of water heated to steam is fitted with a balloon. As the flask cools down, atmospheric pressure pushes the balloon down into the flask.

6. Cartesian Diver

Thermal Expansion

A medicine dropper is partially filled with water so that it is just buoyant in a water filled whiskey bottle. Squeezing the broad sides of the bottle increases the pressure in the bottle which is translated to the just buoyant medicine dropper. The reduced volume of the dropper allows it to sink.

7. Spherical Oil Drop

Spherical Oil Drop

A layered mixture of water and alcohol has a region of density equal to that of vegetable oil. As oil is added to the mixture, it sinks to a stable depth and collects into a large spherical drop under the action of the oil's surface tension.

8. Floating in a Jet Stream

Spherical Oil Drop

A nozzle projecting a jet of high velocity air can suspend various objects such as ping-pong balls, etc. The viscous force of air balance the weight and the low pressure in the jet keeps the object trapped in the air-stream.


1. Drinking Bird

Thermal Expansion

This commercially available toy demonstrates the conversion of thermal energy to mechanical energy. As it dips its beak into a glass of water evaporative cooling induces the rise of volatile liquid from his tail toward his head. As he dunks, the liquid returns to his tail, the bird rises, and the process repeats.

2. Thermal Expansion

Thermal Expansion

A laminated bar made from two different metals fastened in a wooden handle is placed over a flame. The different thermal expansion rates cause the bar to bend.

3. Thermal Energy of Food

Thermal Expansion

A dramatic illustration of the caloric content of food can be conducted by burning a dry-roasted peanut on the end of a long pin. The peanut will burn for about one minute. It's surprising to students to discover the differences in the physical properties of the peanut after it has burned.

4. Mechanical to Thermal Energy

Mechanical/Thermal Converson

A sample of water is heated using a small segment of nichrome wire and a Genecon generator. By measuring the force needed to turn the crank, the lever-arm length, and counting the revolutions needed to raise the temperature of the water 10°C, a comparison of mechanical and thermal energy can be obtained. The student will most likely gain a greater appreciation of 10 cents worth of electricity following this demonstration.

5. Radiometer


The commercially available radiometer has four vanes, white on one side and black on the other. The vanes are mounted in a glass bulb. As light strikes it from the side, the absorbed photons heat the black side which heats the surrounding air molecules which then bounce off the vane imparting momentum.

6. Latent Heat of Fusion

latent heat

A clear plastic pouch of sodium acetate releases latent heat upon crystallization.

Waves & Sound

1. Standing Waves

Standing waves

A DC motor is fitted with a small pulley attached to a swivel. The other end of the rope is attached to a stand with a swivel. As the speed of the motor is adjusted various numbers of nodes and loops can be created. A stroboscope can be used to "stop" the motion.

2. Resonance


A tuning fork is held above a tube, the bottom of which is closed by the water in a 1 L graduated cylinder. The tuning fork and tube are raised and lowered together. The air column in the tube will resonate strongly at odd multiples of one fourth wavelengths of the fork.

3. Freak Pipe

Frequency Pipe

A long corrugated plastic tube, open on both ends, is whirled around in a circle. The fundamental and several harmonics may be excited by whirling it at various speeds.

4. Sympathetic Resonance

Sympathetic Resonance

Two identical tuning forks are mounted on wooden resonance boxes. One of the tuning forks is excited and immediately dampened. The second tuning fork will resonate in sympathy with the first.

5. Garden Trumpet

Trumpet Sound

A 0.3 m section of discarded garden hose will produce a trumpet sound when blown as one blows a trumpet. Changing the length will change the pitch of the "trumpet".


1. Optical Transmitter

Standing waves

A tin can or paper tube is covered on one end by aluminum foil or Mylar film. The aluminum foil should be stretched tight over the tube and held in place with a rubber band or tape. Sing and hold a note (the best you can) into the open end of the tube while reflecting the laser off of the center of the foil. Interesting Lissajous figures will appear.

2. Optical Voice Link

optical voice link

Credit for this technology goes to Alexander Graham Bell (who reportedly used the sun as the light source). A tin can or paper tube is covered on one end by aluminum foil or Mylar film. The aluminum foil should be stretched tight over the tube and held in place with a rubber band or tape. Speak into the open end of the tube while reflecting the laser off of the center of the foil. The modulated signal is then picked up by a solar cell and amplified by a small audio amplifier.