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Encyclopedia of Physics Demonstrations

Mostrando recursos 1 - 20 de 1.194

  1. Demo 16-07 Brownian Motion


    Brownian motion is the random atomic and molecular motion always present in any gas or liquid. It can be rendered visible by inserting smoke into a small cell and watching the motion of the smoke particles resulting from collisions with the air molecules. A microscope can be used to see the motion of the smoke particles, which are shown in Figure 1.
    It should be noted that any change of the motion of the smoke particle cannot be obtained by a collision with one atom of gas. It requires a statistical net of about 10 4 collisions, with air molecules of...

  2. Demo 22-23 Astigmatism


    On-axis astigmatism occurs when the shape of the lens has both a spherically symmetric and a cylindrically symmetric component, so that the focal length in two perpendicular planes is different. In this demonstration such a lens is created by combining a spherical and a cylindrical lens. The focal properties of this "lens" are experimentally investigated using a movable screen, as seen in Figure 1, and an animation further illustrates the effect.
    This type of astigmatism is commonly found in the eye lens. A different type of astigmatism, called off-axis astigmatism, occurs when the lens is focusing non-paraxial rays.

  3. Demo 19-22 Paramagnetism and Diamagnetism


    Ferromagnetic materials are strongly attracted by a magnetic field, and non-magnetic materials are totally unaffected by static magnetic fields. Two other classes of materials exist- paramagnetic materials, which are weakly attracted by magnetic fields, and diamagnetic materials, which are weakly repelled by magnetic fields. This demonstration illustrates the paramagnetism of copper sulfate crystals and the diamagnetism of a bismuth crystal by bringing a strong magnet near samples of these substances using the arrangement shown in Figure 1.

  4. Demo 02-07 Velocity Vector Addition


    This demonstration uses a Ping-Pong ball that is confined in a rolling clear glass tube to illustrate addition of components of displacement.
    We can move the tube with the ball at rest inside it from right to left, causing a horizontal displacement of the ball. If we connect the ball by a taut string to a point at the top end of the tube, moving the tube results in a vertical displacement of the ball equal to its horizontal displacement. The ball then moves with the vector sum of these displacements, at an angle of 45? to either of the individual...

  5. Demo 03-10 X-Squared Spring Energy Dependence


    This demonstration illustrates that the energy stored in a spring is proportional to the square of the distance the spring is compressed. An air track glider is attached to an arm that compresses a spring. When released it moves up the inclined air track, as illustrated in Figure 1. In this case the distance the glider travels up the incline is proportional to its final gravitational potential energy, which is linearly proportional to vertical height and therefore to distance along the incline. The energy stored in the compressed spring increases as the square of the compression, so compression ratios of...

  6. Demo 20-11 Wire and Magnet


    A wire is connected across the terminals of a sensitive galvanometer. When the wire is rapidly passed between the poles of a horseshoe magnet, a potential is induced that can be observed as a deflection of the galvanometer, as seen in Figure 1. The effect of moving the wire in and out of the magnetic field and reversing the magnetic field are shown in the video.

  7. Demo 07-21 Sections of a Cone


    A cone is dissected by cutting it along various orientations. When the cut is perpendicular to the axis, the conic section is a circle. When the cut is parallel to the side of the cone, the section is a parabola. When the cut is parallel to the axis of the cone, the section is a hyperbola. When the angle at which the cone is cut is between that of the circle and that of the parabola, the resulting conic section is an ellipse. These can be seen in Figure 1.

  8. Demo 22-22 Chromatic Aberration / Script


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  9. Demo 14-21 Thermal Conductivity


    Rods of various materials extend outward from a heat sink that is heated up to 100?C and maintained at that temperature. The rods are coated with wax. As heat is conducted along the rods, the wax melts progressively outward on each rod, as shown in Figure 1, illustrating the ability of the material to conduct heat. This demonstration compares the heat conductivity for the following materials and shows that the heat conductivities assume the following order, from lowest to highest (left to right in Figure 1 )- glass, steel, brass, aluminum, and copper.

  10. Demo 08-19 Variable Angle Pendulum


    A physical pendulum is mounted rigidly to a bearing such that the angle of the plane in which the physical pendulum swings can be adjusted, as shown in Figure 1. Increasing the angle q of the plane of the pendulum with respect to the vertical has the effect of decreasing the acceleration of gravity acting on the physical pendulum, so that its period increases- [Equation]
    The period can be measured as a function of angle from the video.

  11. Demo 16-04 Pressure vs. Volume Simulation


    This demonstration shows a model that uses small metal balls to simulate gas molecules. As the volume of the container decreases and the average speed of the "molecules" increases, the rate at which the "molecules" strike the sides of the container increases, so the "pressure" in the container increases, as shown in the video. The apparatus, shown in Figure 1, is available commercially from a number of scientific supply houses.

  12. Demo 23-21 Holograms


    A hologram is a three-dimensional image created by interference of light from a film that has been exposed by laser light. Two holograms are shown in this video, a reflecting white light hologram and a cylindrical laser light hologram. The three-dimensional character of the holograms is clearly shown.

  13. Demo 06-14 Coriolis Effect


    The term "Coriolis effect" is generally applied to the apparent acceleration observed near the surface of the earth due to the earth's rotation, making the surface of the earth a non-inertial frame of reference. A planar model illustrating the Coriolis effect can be obtained by rolling a ball across a slowly rotating turntable, as shown in Figure 1. A more detailed discussion of the Coriolis effect is found in most advanced mechanics books, and a rather detailed mathematical exposition of the subject has been given by Bacon.

  14. Demo 12-11 Buoyant Force


    When a heavy object is submerged in water the water exerts an upward buoyant force on the object. This video shows that the loss of weight of the submerged object is equal to the buoyant force. A weight hanging on a spring balance is lowered into a container of water which is hanging from a second spring balance. The loss of weight of the upper balance is equal to the gain of weight on the lower balance, as indicated in Figure 1 and in the video.

  15. Demo 18-27 Series / Parallel Capacitors


    Two identical capacitors are connected individually, in series, and in parallel to the same voltage source, to study the voltage and the charge on the capacitors in each configuration. We use capacitors of capacitance C, which attain a charge Q when a voltage V is impressed upon them-
    Q = CV
    For the case of capacitors in parallel, the voltage across each is V, so each carries a charge Q, for a total charge of 2 Q. For the case of capacitors in series, the voltage V is shared between the two series capacitors, so each feels only half the voltage, V/2,...

  16. Demo 08-05 Young's Modulus


    Weights are hung on the end of a long wire, and the increases in length measured as a function of the weight, or the tension in the wire. The extension is measured using the deflection of a laser beam by a mirror that tilts as the wire becomes longer, as illustrated in Figure 1. The extension of the wire as a function of tension in the wire is observed to be linear.

  17. Demo 13-13 Bernoulli's Principle


    Water flows along a tube with a constriction near its center, as shown in Figure 1. Because the water flows faster in the section of the tube with a smaller radius, the pressure in that region is reduced, as indicated by the water in the attached sensing tubes. The sensing tube attached to the constriction is initially covered, allowing the students to guess where the water level will be.

  18. Demo 16-17 Thermistor


    A thermistor is a passive component, whose resistance changes with temperature. In combination with the appropriate electronics it can therefore be used to measure temperature. In this demonstration the resistance of a thermistor is measured at different temperatures, as illustrated in Figure 1. The thermistor has a negative coefficient of resistivity, that is, its resistance decreases as the temperature increases.

  19. Demo 07-17 Tippy Top


    A tippy top is an asymmetric top with a partial sphere on one end and a stem on the other end, as shown in Figure 1. When it is spun with its heavy end down, it rises up so that the heavier end is on top, as shown in the figure, apparently defying the law of gravitation.

  20. Demo 07-23 Cavendish Balance


    A Cavendish balance is used to determine the value of the universal constant of gravitation G. Using the actual apparatus, shown in Figure 1, and animation as shown in Figure 2, to illustrate the motion of the balance, the manner in which the apparatus functions is illustrated on the video.

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