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Class Demonstrations available at NMT physics

Demos are organized by categories: Mechanics, E & M, Optics, Waves, Thermodynamics, Various, Subcategories are some times added to further sort the demos. An effort has also been made to tag the demos with labels that describe recurrent themes for which they have been used. The tags associated with a demo are shown to the right of its name, in the "tags" column. The tag list below is a compilation of all tags used in this page and could help in finding demonstrations using your browser searching tool.

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Mechanics, Kinematics, Projectile Motion, Waves, Sound, Optics, Geometric Optics, Lenses, Electromagnetism, Optics, Light, Forces, Gravity, Electrostatics, Charge, Thermodynamics, First Law, Adiabatic, Pressure, Temperature., Newton's Laws, Conservation of momentum, Conservation of energy, Elastic Collisions, Collisions., Electric Charge, Measurements, Faraday, Electric Field, Electric Potential, Capacitors, Oscillations, Energy, Conservation, Angular Motion, Angular Momentum, Troque, Torque, Electricity, Capacitor, Energy conservation, Angular velocity, Rotational Dynamics, Geometric optics, Mirrors, Electric current, resistivity, conductance, magnetism, optics, waves, interference, Gas law, , induction,Faraday's law, Gases , Gas law, Eddy current , magnetic breaking , induction, Eddy currents, Faraday's law, Energy, Projectile Motion , Tension, Weight , inertia

Feel free to contact me with any questions regarding the information on this page (carlos.labmanAtgoogle.com).


ID Mechanics subcat tags Top
d0001 Monkey and the Hunter:
Demonstrates a classic projectile motion problem. Namely that a projectile aimed directly at a hanging target willhit the target. The target is in the projectile range and it is releasedat the moment when the projectile is launched. more		 kinematics Mechanics, Kinematics, Projectile Motion Top
d0002 Popper Car:
Demonstrates a classic projectile motion concept. Namely that horizontal and vertical motion are independent. For this purpose, a vertical launcher is mounted on a car that moves at constant speed on a "frictionless" track. more		 kinematics Mechanics, Kinematics, Projectile Motion Top
d0003 Shoot the Instructor:
Demonstrates a classic projectile motion problem. This demo uses a custom made launcher that is more powerful than the PASCO launcher. It can launch PASCO plastic balls across Workman 101.Typically the students are asked to locate a target in the room, measure its distance from the launcher and set the launcher to the appropriate angle to hit the target This demo is particularly effective when the target is the instructor (who should be wearing protective goggles). more		 kinematics Mechanics, Kinematics, Projectile Motion Top
d0008 The Penny and the Feather:
Demonstrates that acceleration due to gravity is independent of mass, which implies that gravitational force acting on an object is proportional to its mass. The idea is to convince students that objects falling trough a media (the atmosphere) fall at differentrates due to resistance in the media. For this purpose, we first let the students observe a penny and a feather fall inside a transparent tube fill with air at atmospheric pressure. Then, weevacuate the air from the tube and let the students observe the these objects falling under the new conditions. more		 apps Mechanics, Forces, Gravity Top
d0011 Galilean Canon:
This is a dramatic illustration of conservation of momentum. In this demo, two bouncing balls are dropped, one on top of the other. The masses of the two balls are different and the smaller ball is on top. When the larger balls reaches the ground, it will bounce back, while the smaller ball is still going downward. The two balls then collide. The analysis of the collision is a typical problem that could be used to practice the usage of conservation laws. The analysis of the collision is simpler in the reference frame of the largest ball. more		 NA Newton's Laws, Conservation of momentum, Conservation of energy, Elastic Collisions, Collisions. Top
d0014 Bowling Ball Pendulum:
This is demo is typically used to illustrate conservation of energy in freshman physics. In this demo, a pendulum is formed by a bowling ball of about 5kg attached to string about 2.5 m long, which is hung from the ceiling of the classroom. The idea is that students observe the conversion from gravitational potential to kinetic energy and vice versa. More importantly, the students should notice that at the end of a cycle the energy is back to where it was -perhaps a bit less due to some dissipation. A touch of drama is added if the ball is released from rest at a point close to the face of a student -make sure the student does not lean forward to meet the returning ball. Have the student sit on a chair about half a meter higher from the lowest point of the pendulum. Standing behind the student bring the bowling ball close to the student's nose. Release the ball while the rest of the group watch - just before releasing the ball ask some of spectators to be ready to call 911, to add to the suspense. It will be more engaging if you can make a movie and the project it on the screen for analysis. more		 NA Mechanics, Energy, Conservation, Oscillations Top
d0017 Bicycle Wheel:
The axis of the bicycle wheel has a handle on each side that allows for an easy grip. For setting the wheel on a fast spin, a spool is mounted on the axis of the wheel, where a string can be wound up. It is also very easy to attach a string at the end of the axis to apply a torque to the wheel. Grabbing the wheel axis with the left hand let the right hand free to spin the wheel and, more importantly, to illustrate the use of the right hand rule to determine the direction of the angular velocity associated with the rotation of the wheel. Once the students are comfortable in describing rotation in terms of angular velocity or angular momentum , it is easy to demonstrate how the change of angular momentum is associated with a torque. For this purpose simply attach a string to the end of the axis of the wheel, then grab the axis of the wheel with one hand and spin it with the other, grab the string with your free hand and let go the axis of the wheel. The axis of the wheel will remain horizontal, but it will start to rotate around the vertical, in response to the torque being applied. more		 NA Mechanics, Angular Motion, Angular Momentum, Troque Top
d0018 Bicycle Wheel and Metal Rotating platform:
This demonstration illustrate conservation of angular momentum along the z-direction. It requires a bicycle wheel with handlesand a rotating platform. Typically this demo is a hands-on exercise for students in physics 121 lab. Various initial conditions are possible: the simplest one is to start with the angular momentum confined to the wheel and pointing in the z-direction. Keep the platform from rotating while spinning the bicycle wheel, step onto the platform and held the bicycle wheel over head with its axis aligned with vertical. Once this initial state is set, one can tilt the wheel axis in any direction and discuss the resultant rotation of the system (wheel + person). Although the combined moment of inertia(wheel + person) is slightly different from the initial configuration this should not affect much the results. An interesting variation, starting from the same configuration, is simply stopping the wheel. \n A different initial condition is to start with the angular momentum on the horizontal plane, say with the angular momentum perpendicular to our chest. In this configuration we grab, with both hands, one side of the wheel axis. Starting from this initial configuration, we can tilt the axis toward the vertical, either by bringing the wheel up or down. Going from the initial to the final state in this case, will change significantly the combined moment of inertia. Hence if will be difficult to disentangle the effects. A slight variation that keeps the combined inertia close to its initial value and the angular momentum still on the horizontal plane is to start with the angular momentum parallel to our chest. In this case we still hold the wheel with both hands, but we grab the wheel on both sides of the axis. \n Then, we just tilt the axes to point the angular momentum up or down. Starting with the angular momentum on the horizontal plane allow us to talk about why the horizontal component is not conserved and how this relates to an external torque. In all these cases, it may be better to start by asking the students to predict the resultant rotation based conservation of angular momentum and then perform the demo. The student should be encourage to describe the resultant rotation in terms of the angular velocity vector . If you have done the bicycle wheel (d0017) demo,then they know how to get the direction and sense of the angular velocity vector for a rotating object. Please feel free to experiment, there are many more possibilities for the initial conditions and hence to have fun with this equipment. more		 NA Mechanics, Angular Motion, Angular Momentum, Torque Top
d0019 Angular momentum and the Ice skater:
This demonstration illustrate conservation of angular momentum along the z-direction. Basically, the students observe how, by changing the moment of inertia of the system, the angular velocity is forced to change in order to conserve the initial angular momentum --the way ice skaters and divers control their rate of rotation. Typically this demo is a hands-on exercise for students in physics 121 lab. The implementation is done using a rotating platform with a stool fit to it. This demo requires a couple of 3 or 4 pound dumbbells. Recruit a volunteer and sit her/him on the stool and ask him to hold the dumbbells -one in each hand- close to the chest. Gently set the platform on an easy rotation. Starting with the smallest value of inertia (dumbbells close to chest) will only slow down the rider as she/he extends its arms away from the chest. If the rider can handle it, you can start her/him with the largest moment inertia --be careful. more		 NA Mechanics, Angular Motion, Angular Momentum, Torque Top
d0021 Loop-the-Loop:
In this demonstration, we use the contraption shown in figure (LINK to figure) to illustrate how methods based on energy conservation can be used to solve problems. The contraption has two long aluminum tracks parallel to each other mounted on a long wooden platform (3.35m). The geometry of the tracks is basically of a ramp on each end connected by the mid section. One track is straight with the ramps connected by a flat section. The other track has a loop 0.535m in diameter in its mid section . The tracks are made of C-profile facing up and can fit either an sphere (2.54 cm diameter) or a wheeled metal car. The car's wheels have a small moment of inertia and roll on top of the edges of the track. Because these objects are actually rolling, the friction with the track is keep to a minimum. Nevertheless, the energy lost to friction can be calculated using the straight track. The relevant distances for the tracks are given in this diagram ( LINK to diagram). more		 NA Mechanics, Energy conservation, Angular velocity, Rotational Dynamics Top
d0032 Some demos:
The Pictures were kindly provided by Dr. Richard Sonnenfeld.They represent a sample of some demos that he had used in the past. more		 NA Energy, Projectile Motion , Tension, Weight , inertia Top
ID E & M subcat tags Top
d0009 Interaction between neutral and charged objects.:
Demonstrates that charges of opposite signs attract each other. Start by rubbing a piece of acrylic with rabbit fur and then bring the acrylic close to a bunch of small pieces of paper. Notice how the paper flies over toward the acrylic. Now put a aluminum soda can over a flat surface, so it is able to roll, then bring the chargedacrylic piece close to the can and slowly move it away from the can. Observe how the can follows the acrylic. In order to make sense of the observations, one has to remind the audience that neutral objects are not void of charge, but are in a state of charge balance. Also thattheir charge can be reorganized in response to an external electric charge. For instance, polarization of molecules in non-conducting materials (like the pieces of paper and Styrofoam) and mobility of electrons in the case of conductors (like the soda can). This demonstration is perhaps more effective if you show the students that regardless of the type of charge the neutral object is attracted to the charged object. See the "Electric Charge" demo to show that two charged objects have opposite charge. more		 electricity Electrostatics, Charge, Forces Top
d0012 Faraday Ice pail:
This is PASCO demonstration that can be used to illustrate charge transfer by contact. The demonstration uses a Faraday ice pail, which basically consist of two isolated concentric cylinders made of a metallic mesh. In order to avoid charge induction from the environment on the inner cylinder, the outer cylinder must be connected to a good ground. The inner cylinder is connected to an electrometer ,which is more sensitive than our electroscopes and is able to measure tiny charges in the inner cylinder. Charge is induced in the inner cylinder when a charged object is brought inside it. The PASCO kit also provides a set of probes: one metallic and two made from different insulating materials. Rubbing the two insulating materials let them charged with opposite charges. The magnitude of the charge is enough to be detected by the electrometer even on rainy days. The metal probe can be used to sample charge density from a charge object. The electrometer output can also be send to a computer for processing, but I have not yet explored this capability. more		 NA Electrostatics, Electric Charge, Measurements, Faraday Top
d0013 Electrostatic Pendulum:
This demonstration, allows for a nice visualization of the electric field inside a parallel plate capacitor. The idea is that an electric charge will be push by the electric field towards one of the capacitor's plates, according to their polarity. The twist is that the charged object between the plates is a graphite-covered sphere, which makes it a good conductor. Once the sphere touches the plate, it deposits its charge and acquires charge of the opposite sign from that plate, and is therefore immediately repelled. The electric field inside the capacitor will now pushed the sphere towards the other plate where the story repeats. The end result is an oscillatory motion of the sphere inside the plate capacitor. Note that there is no equilibrium point for the sphere and the force on the sphere due to the electric field is constant inside the capacitor - the oscillation is not harmonic. The capacitor for this demo is a PASCO variable capacitor, which allows us to vary the distance between the plates and therefore the magnitude of the electric field. Hence, by changing the distance between the plates you can vary the frequency of the oscillator. The graphite-covered sphere (also from PASCO) is hanging from a fishing line right at the center of the capacitor. The potential difference is supplied by a DC high-voltage-low-current source. Changing the potential difference, is another way to control the electric field and therefore the frequency of the oscillation. The voltage range is typically between 1kV and 3kV. The currents are very low, since the sphere can only carry a few micro Coulombs per oscillation, and the frequencies are less that 100 Hz. more		 NA Electrostatics, Electric Field, Electric Potential, Electric Charge, Capacitors, Oscillations Top
d0015 Van de Graaff:
The Van de Graaff apparatus allows for a variety of quick demonstrations that can be used to illustrate the charge and electric field interactions. Our's is a PASCO Van de Graff that can generate High voltages (up to 400kV). We typically use it in conjunction with several accessories. For instance, a discharge sphere is used to get the attention of the students: charge buildup on the Van de Graaff dome spark across the air into the discharge sphere. We can easily obtain sparks at least 10cm on a good dry day --the air's dielectric strength is about 30kV/cm. To illustrate that like charges repel, we can put the PASCO electrostatic plume on top of the Van de Graff dome. The plume's ribbons become charged and they will stand on. Perhaps a more vivid display of repelling of like charges is obtained with a stack of small aluminum cups put on top of the Van de Graaff dome. As soon as charges start getting into the dome, they will be transferred to the aluminum cups making them repel each other. Because gravity is holding the stack down, the cups will start flying off the dome, one by one starting from the top. We also have a PASCO electrostatic whirl accessory that can be used to illustrate variations in electric field due to curvature. Another attention grabber is the lighting of a fluorescent tube. When the tube is held close to (but not touching) the charged dome and is radially oriented with respect to the dome, it will light up. This is a good illustration of the electric field that is build up radially from the dome. The gradient in this field creates potential difference that is large enough to move charges inside the tube. Of course there are many more demos that can be done with our Van de Graaff apparatus, please share them. more		 NA Electrostatics, Electric Field, Electric Potential, Electric Charge Top
d0016 Wimshurst Machine:
The Wimshurst machine is an electrostatic generator based on induction (as opposed to friction). It can generate a large potential, which can be increased using a couple of Leyden Jars (capacitors). We can easily generate sparks of one or two centimeters long. The machine allow us to illustrate how mechanical energy can be readily converted into electrical energy. Furthermore, the Lynden jars allow us to demonstrate how electric energy can be stored for later release. We normally use the Wimshurst machine as a high voltage and steady current source to feed a Crook's tube. In this case, once the circuit is established, there is a beam of charged particles running down the Crook's tube. Inside this tube there is a phosphorus screen that runs along the tube, almost parallel to it. Collisions of the charged particles with a phosphorus screen generate a nice trace of the beam. We can easily see how a magnetic field alters the direction of the beam. In addition, given the polarity of the magnet, we can determine the sign of the charges in the beam. We should be able to convince the students that the particle beam is an electron beam. more		 NA Electrostatics, Electric Field, Electric Potential, Electric Charge, Capacitors, Oscillations Top
d0020 Charge in a Capacitor:
This demonstration illustrate how the capacitance value determines the amount of charge a capacitor can hold, for a given voltage. In this demo, we use a PASCO variable capacitor --basically two circular aluminum plates facing each other, whose separation distance can be varied. One plate is connected to a good ground, while the other is connected to an electroscope. Starting with the plates a few centimeters apart, charge the plate until the electroscope shows evidence of the charge. Then simply vary the distance between the plates and observe how charge flows from the capacitor to the electroscope as the capacitance is reduced and flows back to the capacitor as you increase the capacitance. more		 NA Electricity, Charge, Capacitor Top
d0023 Electrical Resistance and Temperature:
This demo illustrate how the electrical resistance of a material depends on temperature. A sample of material is warm up with a hair dryer, then cool down with liquid nitrogen. A sample of copper wire winded in a coil works well to illustrate the typical behavior of electrical resistance in metals. The response of a thermistor can be used to illustrate how different materials can have very different behaviors. more		 NA Electric current, resistivity, conductance Top
d0024 e/m apparatus:
This demo is typically used to illustrate the effect of magnetic fields over the motion of electric charges. The demo consist in showing the deflection of an electron beam by a magnetic field.The beam of electrons is produced inside an electron tube that shuts an stream of electrons in the horizontal direction. Low pressure gas inside the tube makes the electron beam visible. The tube sits in between two Helmhotlz coils, which produce a magnetic field perpendicular to the direction of the electron beam. Increasing the current on the coils increases the magnetic field, which makes the change in direction of the electron beam more pronounced. The intensity of the magnetic field can be made strong enough to force the beam on a circular path, whose radius can be measured.

The current through the coils is supplied by an independent DCpower supply and can be varied and measured. The voltage that accelerates the electrons is provided by a high-voltage low-current DC power supply. This high voltage can also be varied and measured. The electrons are supplied by a heated element in the electron tube. This element is heated using an independent low-voltage AC power supply, which is integrated into the high-voltage DC supply. more

 NA Electricity, magnetism Top
d0027 The Big Old Galvan-o-meter:
This demo illustrate that a changing magnetic fluxthrough a closed electric circuit induces a voltage (emf) in the circuit. A coil of copper wire whose ends are connectedto a big galvanometer serves as the electric circuit.The magnetic flux is provided by a bar magnet and the change in flux is due to the relative motion between the magnet and coil. It is easy to show that no emf is induced when the flux is constant (no motion) and that the relative motion is what is relevant for induction. more		 magnetism induction,Faraday's law Top
d0029 Eddy Pendulum:

This demonstration illustrates what is known asdissipative magnetic breaking via induced Eddy currents. It consistsof a physical pendulum, composed of a wooden rod with a metallic slab attached to its swinging tip. As it swings, the tip passes between the poles of a large C magnet. In this configuration, breaking occurs because of the change in the magnetic flux though the area of the metal slab. This change induces currents around loops within the area of the metal. The direction of the current in those loops is determined by Lens' law. The result is that the metal slab looks like a magnet, whose polarity is opposite to that of the external magnet.

Although Eddy currents are not actually measured, their effect can beeasily seen by comparing the rate at which the pendulum looses energywhen there is a magnet present and when it is absent. However, in orderto convince the students that the invisible Eddy currents are responsiblefor dissipating the energy, we compare the magnetic breaking between ouroriginal pendulum and one whose slab is made by joining thin stripes ofmetal electrically insulated from each other. The insulation of thestripes prevents the formation of large Eddy loops, which in turns reducesthe magnetic breaking.

more

 magnetism Eddy current , magnetic breaking , induction Top
d0030 Jumping Rings:

This demonstration shows, quite dramatically, the induction of Eddy currents. It consists of an strong electromagnet, whose iron core sticks a few inches out of the coil, and a set of metallicrings that fit around the iron core.The coil connects directly to an electrical outlet and the alternating current produces an alternating magnetic flux trough the metallic rings. The sense of the induced current in the ring is governed by Lens' law resulting in the ring behaving like a magnet with the opposite polarity to that of the iron core of the coil. The repulsion between these magnets propels the ring into the air.

The magnitude of the induced current can be increased by reducing the electrical resistance of the rings, which can be accomplished by cooling down the ring. Using liquid nitrogen for this purpose is veryeffective.

more		 magnetism Eddy currents, induction Top
d0031 Eddy's Tube:

This demonstration illustrates what is known asdissipative magnetic breaking via induced Eddy currents. It consistsof a neodymium magnet falling inside a metallic tube.

In this configuration, breaking occurs because of the changein the magnetic flux throughout the cross section of the tube. This change induces electrical currents around loops on the circumference of the tube. The direction of the current in those loops is determined by Lens' law. The result is that segments above and bellow the falling magnet behave like magnets themselves, but with opposite polarity: the segments below with the same polarity as the falling magnet and segments above, with the opposite.

In order to make it clear that it is the interaction between the magnetand the tube that produces the breaking, it is worth to compare the falling rate through the tube between a penny and the magnet. If you like, you can use a stop watch, but it is not necessary --the difference is quite noticeable. more		 magnetism Eddy currents, magnetic breaking , Faraday's law Top
ID Optics subcat tags Top
d0005 Covered Lens:
Demonstrates that typical key rays shown in diagrams are not the only ones contributing to image formation. You can also illustrate that real images are inverted. more		 NA Optics, Geometric Optics, Lenses Top
d0006 Diffraction and Interference:
Demonstrates wave diffraction and interference using a coherent light source. This demo uses the PASCO kit. You can easily show single slit diffraction patterns and illustrate how patternsfrom two slits interfere. Also, the effects of changing the apertureof the slit and the spacing between slits can be shown. The kit has also two different lasers: green and red, which allows you to illustrate the effects of wavelength on the patterns. more		 NA Electromagnetism, Optics, Waves, Light Top
d0022 Geometric Optics:
This demonstration can be used to illustrate many concepts in geometric optics: reflection, refraction, etc. It consist of a light box mounted on a white flat platform and an optical set from Arbor Scientific. more		 NA Geometric optics, Lenses, Mirrors Top
d0025 Michelson Interferometer:
This demonstration illustrate a classic interference experiment in physics. A PASCO set that is specifically designedfor this purpose is used in this demonstration. It effectively illustrates how waves interfere when they are in and out of phase at a given location.This demo is part of a lab experiment in physics 221. It basically consists in splitting a laser beam into two rays (with a semitransparent mirror), changing the path traveled by one of the resulting rays (with the help of a movable mirror), recombining the rays, and projecting the recombined beam on a screen. A micrometer is used to move the mirror, which allows a precise variation on the length of the path travel by the rays. more		 waves optics, waves, interference Top
ID Waves subcat tags Top
d0004 Beats:
Demonstrates wave interference using sound waves. Two sine waves with audible frequencies are generated by two signal generators and the output is feed to a single speaker. When the frequencies are close enough, the students can hear the beats and count them using their stop watches. The output from the generators is also passed to an oscilloscope where the frequencies of the signal generators can bemeasured. The beats can also be visualized in the scope and if the twosources are made to produce waves with the same amplitude, then totaldestructive interference can be illustrated. Also given one of the frequencies feed to the speaker, you may also ask the students to estimate the frequency of the other source, just by counting the beats. more		 NA Mechanics, Waves, Sound Top
d0007 Doppler Effect:
Demonstrates the Doppler effect for a moving sound source. In this demo the instructor ask the students to listen to a small battery power sound source, while the source is not moving and then proceeds to swing the source above his head. The students should be able to listen to the variations in frequency due to the motion of the source. more		 NA Mechanics, Waves, Sound Top
ID Thermodynamics subcat tags Top
d0010 Bottled Clouds:
Illustrate the temperature drop of a sample of gas during adiabatic expansion. The temperature drop is manifested withthe formation of tiny water droplets suspended in the air inside the bottle. For this demo, we add some liquid water to a transparent jar and shake it well to saturate the air inside the jar (100\% relative humidity). We then increase the pressure in the bottle by some 20 psi. Finally, with a quick motion, we release the pressure from the bottle. The sudden release of pressure is important to insure that the expansion is close to being adiabatic. The temperature drop in the sample of saturated air should be enough to bring the sample to supersaturation. Supersaturated water vapor will condense over condensation nuclei and with enough condensation nuclei, there will be a large collection of tiny droplets to form a little cloud inside the jar. Normally there are plenty of condensation nuclei present in the air. However, to make the demonstration more dramatic, you could add some nuclei of your own (a smoking burned-down match or a few drops of rubbing alcohol are fine). The cloud can be visualized better by scattering some light from a lamp (or flashlight). more		 NA Thermodynamics, First Law, Adiabatic, Pressure, Temperature. Top
d0026 Absolute Zero Demonstrator:
This demo uses a constant volume gas apparatus by TekSys toillustrate the temperature-pressure relationship for a gas. The name of this demo is a bit misleading, because the gas is never evenclose to zero Kelvin. Instead this demo allows you to infer (by extrapolation) what would happen at zero kelvin. The demonstration basically consist in recording and plotting the pressure for a set of predetermined temperatures, that correspond to well known phase transitions of water and CO-2 (dry ice). more		 NA Gas law, Top
d0028 Thermo Can Crush:
This demo shows, quite dramatically, the power of atmospheric pressure. The basic idea is to reduce the pressureinside a thin-walled container and watch how atmospheric pressure crushes the container. A quick reduction in pressure is achieved by displacing the air inside the container with water vapor and then condensing the vapor, by reducing the container's temperature.An easy way to do this is to add a bit of liquid water to a soda canand then boil the water; as soon as steam comes out of the can, use atongue to grab the soda can, invert it, and dip the opened end of thecan in a cold bath (ice water work best, but room temperature water is good enough). All water vapor filling the container will condense in just a tiny drop reducing the pressure inside the can; the pressure imbalance will be enough to crush the can. more		 NA Gases , Gas law Top
ID Various subcat tags Top