Geyser - Cyclic hot water fountain

<div dir="ltr" style="text-align: left;" trbidi="on"><b><span style="font-size: large;"><br /></span></b><div style="text-align: center;"><b><span style="font-size: large;"><br /></span></b></div><div style="text-align: center;"><!-- InstanceBeginEditable name="doctitle" --></div><!-- FACEBOOK OG TAGS --><!-- / FACEBOOK OG TAGS --><!-- InstanceEndEditable --><!-- InstanceBeginEditable name="head" --><!-- InstanceEndEditable --><br /><div class="right_column" style="text-align: center;"><div class="big_illustration"><b><span style="font-size: large;"><img align="bottom" height="280" src="http://www.exploratorium.edu/snacks/geyser/geyser_130x266.gif" width="130" /></span></b> </div><div class="subjects"> <b><span style="font-size: large;"><img align="bottom" border="0" height="75" src="http://www.exploratorium.edu/snacks/images/fluids.gif" width="60" /> <img align="bottom" border="0" height="75" src="http://www.exploratorium.edu/snacks/images/heat.gif" width="60" /></span></b> </div></div><div class="title"> <span style="color: red;"><u><b><span style="font-size: large;"> Geyser</span></b></u></span> </div><div class="subtitle"> <b><span style="font-size: large;"> </span></b></div><div class="subtitle"><b><span style="font-size: large;">Cyclic hot water fountain</span></b></div><div class="subtitle"><b><span style="font-size: large;"> </span></b> </div><div class="short_description"> <b><span style="font-size: large;">Natural geysers form when underground chambers fill with water and are heated geothermally. When the water is heated to its boiling point, the geyser erupts, spewing its contents, and the cycle starts again. </span></b></div><div class="short_description"><b><span style="font-size: large;"> </span></b> </div><div class="materials_section"><div class="materials_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/materials.gif" width="255" /> </span></b></div><div class="materials"> <ul><li><b><span style="font-size: large;">Ring stand</span></b></li><li><b><span style="font-size: large;">Metal ring</span></b></li><li><b><span style="font-size: large;">Hot plate or other heat source</span></b></li><li><b><span style="font-size: large;">Plastic food container</span></b></li><li><b><span style="font-size: large;">Glass tubing (.5 to 1 meter in length)</span></b></li><li><b><span style="font-size: large;">Boiling or Erlenmeyer Flask</span></b></li><li><b><span style="font-size: large;">One-hole rubber stopper</span></b></li><li><b><span style="font-size: large;">Plumber'sputty</span></b></li><li><b><span style="font-size: large;">Timing device (stopwatch or clock)</span></b></li></ul></div></div><div class="assembly_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="23" src="http://www.exploratorium.edu/snacks/images/assembly.gif" width="256" /></span></b> </div><div class="assembly"> <br /><b><span style="font-size: large;">1) Drill a hole in the center base of your plastic container (a sharp, pointed knife twirled in a circle makes a great drill). The hole should be just large enough for the glass tubing to be snugly inserted.<br /><br />2) Position an unplugged hot plate next to the base of a ring stand and set a boiling flask filled with water on top of the heating unit.<br /><br />3) Carefully insert one end of the glass tubing into the top of a one-hole rubber stopper. Slide the glass tubing until it is flush with the bottom of the stopper.<br /><br />4) Cap the flask with the assembled stopper and glass tubing.<br /><br />5) Slide a metal ring onto the ring stand and over the glass tubing (no need to tighten yet).</span></b><br /><br /><b><span style="font-size: large;">6) Insert the opposite end of the glass tubing into the base of the plastic container. Adjust the glass tubing so that the end extends several centimeters above the bottom of the container, but well below the container's rim. To prevent leakage, seal any gaps where the glass tubing and container meet with plumber's putty.<br /><br />7) Place the center of the ring directly under the plastic container and tighten securely. This ring will be supporting the weight of the container and several cups of water.<br /><br />8) Pour cool water into the plastic container. Fill the container with enough water so that the top of the glass tubing is a centimeter or two below the water's surface.<br /><br />9) Turn on the heating element and stand back.<br /><br />10) After the geyser "blows," it will reset itself by sucking the cool water from the plastic container back into the flask. Several eruptions will occur before the plastic container of water gets too hot and the temperature difference between the water in the flask and the water in the plastic container is not great enough to refill the system. When this happens, turn off or unplug the heating element and wait until the water in the plastic container cools.</span></b><br /><br /> </div><div class="to_do_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/tdn.gif" width="256" /></span></b> </div><div class="to_do"> <ul><li><b><span style="font-size: large;">From a safe distance, watch what happens as the water heats and boils.</span></b></li><li><b><span style="font-size: large;">How many different cycles can you discover in this geyser?</span></b></li><li><b><span style="font-size: large;">Use your stopwatch to time and record the duration between eruptions and any other cycles you observe.</span></b></li></ul></div><div class="whats_going_on_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="24" src="http://www.exploratorium.edu/snacks/images/wgo.gif" width="256" /></span></b> </div><div class="whats_going_on"> <div class="whats_going_on"><br /></div><div class="whats_going_on"><b><span style="font-size: large;">There are three main phases to this geyser's cycle: Heating, Erupting and Refilling.<br /><br /> Heating:<br /> The heating time required to cause an eruption is based on two main factors: The energy output of the heat source and the length of glass tubing. The longer the glass tube, the more pressure there is on the flask of water. The more pressure there is, the more heat it takes for the water to boil and the longer it takes for the geyser to erupt.<br /><br />Erupting:<br /> Steam expands to over 1500 times its original volume and launches water out of the geyser (As the liquid begins to flow up the tube, it reduces the pressure in the chamber below. This in turn reduces the boiling point of the water causing a rapid conversion of liquid into steam).<br /><br />Refilling:<br /> After the eruption slows, a small amount of cool water in the upper container will flow down into the flask, causing the steam in the tube and flask to condense. This decreases the pressure inside the apparatus, allowing the atmosphere outside to push more water down into the flask.</span></b></div><div class="whats_going_on"><br /></div></div><div class="etcetera_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="16" src="http://www.exploratorium.edu/snacks/images/etcetera.gif" width="256" /></span></b> </div><div class="etcetera"><b><span style="font-size: large;"> </span></b><div class="etcetera"><br /></div><div class="etcetera"><b><span style="font-size: large;">Yellowstone National Park in northwestern Wyoming contains approximately 400 of the world's 700 geysers. Steamboat Geyser, located in Yellowstone's Norris Basin, is currently the world's tallest erupting geyser. Major eruptions can be over 350 feet tall.</span></b></div><div class="etcetera"><br /></div></div></div>

Science Snacks Geyser - Cyclic hot water fountain

  Geyser   Cyclic hot water fountain   Natural geysers form when underground chambers fill with water ...

Read more »

Gas Model - Caged molecules do their thing.

<div dir="ltr" style="text-align: left;" trbidi="on"><b><span style="font-size: large;"><br /></span></b><b><span style="font-size: large;"><br /></span></b><!-- InstanceBeginEditable name="doctitle" --><br /><!-- FACEBOOK OG TAGS --><!-- / FACEBOOK OG TAGS --><!-- InstanceEndEditable --><!-- InstanceBeginEditable name="head" --><!-- InstanceEndEditable --><br /><div class="right_column"><div class="big_illustration" style="text-align: center;"><b><span style="font-size: large;"><img align="bottom" height="245" src="http://www.exploratorium.edu/snacks/gas_model/gas_model_1_173x245.gif" width="173" /></span></b> </div><div class="subjects" style="text-align: center;"> <span style="color: red;"><u><b><span style="font-size: large;"><img align="bottom" height="75" src="http://www.exploratorium.edu/snacks/images/chemistry.gif" width="60" /> <img align="bottom" height="75" src="http://www.exploratorium.edu/snacks/images/heat.gif" width="60" /></span></b> </u></span></div></div><div class="title"><span style="color: red;"><u> <b><span style="font-size: large;"> Gas Model</span></b></u></span> </div><div class="subtitle"> <b><span style="font-size: large;"> </span></b></div><div class="subtitle"><b><span style="font-size: large;">Caged molecules do their thing. </span></b></div><div class="subtitle"><b><span style="font-size: large;"> </span></b> </div><div class="short_description"> <b><span style="font-size: large;">The atomic theory of matter tells us that a gas is made up of tiny particles called <i>atoms</i> (or <i>molecules</i>, which are combinations of atoms), which are constantly in motion, smashing into each other and the walls of their container, if there is one. Here is a highly visual model of this idea. </span></b></div><div class="short_description"><b><span style="font-size: large;"> </span></b> </div><div class="materials_section"><div class="materials_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/materials.gif" width="255" /> </span></b></div><div class="materials"> <ul><li><b><span style="font-size: large;">12 or more Styrofoam balls, <img align="top" border="0" height="1" src="http://www.exploratorium.edu/snacks/images/clear.gif" width="13" />approximately 1-1/4 inches (3 cm) in diameter (available in craft or fabric stores), or table tennis balls.</span></b></li><li><b><span style="font-size: large;">A paintbrush.</span></b></li><li><b><span style="font-size: large;">Latex paint.</span></b></li><li><b><span style="font-size: large;">A small rodent cage with wire mesh on all sides. (Two plastic strawberry baskets or utility baskets with open grid sides may also be put together to form a cage.)</span></b></li><li><b><span style="font-size: large;">Short pieces of wire or twist ties.</span></b></li><li><b><span style="font-size: large;">A hair dryer, fan, or other blower.</span></b></li></ul></div></div><div class="assembly_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="23" src="http://www.exploratorium.edu/snacks/images/assembly.gif" width="256" /></span></b> </div><div class="assembly"> <br /><b><span style="font-size: large;">15 minutes or less)</span></b><br /><br /><b><span style="font-size: large;">Paint one of the balls a bright color, using latex paint (because oil-based paint dissolves Styrofoam). Place the balls in the cage and secure the door of the cage with short pieces of wire or twist ties.</span></b><br /><br /> </div><div class="to_do_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/tdn.gif" width="256" /></span></b> </div><div class="to_do"> <br /><b><span style="font-size: large;">(15 minutes or more)</span></b><br /><br /><b><span style="font-size: large;">Hold the blower under the cage and blow air up through it. The moving air will agitate the balls, simulating the kinetic behavior of a gas. Watching the colored ball will allow you to follow the motion of a single "molecule."</span></b><br /><br /><b><span style="font-size: large;">By adjusting the speed of the blower from the cage, you can simulate heating and cooling a gas. The faster the balls are moving, the hotter the gas.</span></b><br /><br /><b><span style="font-size: large;">Listen for the clicking of the balls against the walls of the cage. At lower "temperatures," the clicking is quieter and occurs at a slower rate.</span></b><br /><br /> </div><div class="whats_going_on_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="24" src="http://www.exploratorium.edu/snacks/images/wgo.gif" width="256" /></span></b> </div><div class="whats_going_on"> <div class="whats_going_on"><br /></div><div class="whats_going_on"><b><span style="font-size: large;">Adding heat (simulated by the blower) to a gas increases its internal energy. The molecules of the gas move faster and strike the walls of their container more often, yielding an increase in pressure (force per area). This increased pressure is simulated by the faster motion of the balls, which strike the sides of the cage more often. Cooling the gas (moving the blower farther from the cage) lowers the internal energy, slowing the motion of the molecules, and thus lowering the pressure.</span></b></div><div class="whats_going_on"><br /></div></div><div class="etcetera_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="16" src="http://www.exploratorium.edu/snacks/images/etcetera.gif" width="256" /></span></b> </div><div class="etcetera"><b><span style="font-size: large;"> </span></b><br /><b><span style="font-size: large;">You may want to try this Snack using cages of different volumes or try nesting baskets to change their volume. In this way, you can model the ideal gas law by changing temperature, pressure, and volume.</span></b><br /><br /><b><span style="font-size: large;">If you blow air on one side of the bottom of the cage and not the other, the balls will eventually "condense out." That is, they will form a pile on the side away from the blower, where it is "cooler."</span></b><br /></div></div>

Science Snacks Gas Model - Caged molecules do their thing.

  Gas Model   Caged molecules do their thing.    The atomic theory of matter tells us that a gas...

Read more »

Fog Chamber - Make a portable cloud in a bottle. Now you see it; now you don't!

<div dir="ltr" style="text-align: left;" trbidi="on"><div style="text-align: center;"><b><span style="font-size: large;"><br /></span></b></div><div style="text-align: center;"><b><span style="font-size: large;"><br /></span></b></div><div style="text-align: center;"><!-- InstanceBeginEditable name="doctitle" --></div><!-- FACEBOOK OG TAGS --><!-- / FACEBOOK OG TAGS --><!-- InstanceEndEditable --><!-- InstanceBeginEditable name="head" --><!-- InstanceEndEditable --><br /><div class="right_column" style="text-align: center;"><div class="big_illustration"><b><span style="font-size: large;"><img align="bottom" height="214" src="http://www.exploratorium.edu/snacks/fog_chamber/fog_chamber_1_455x214.gif" width="455" /></span></b> </div><div class="subjects"> <b><span style="font-size: large;"><img align="bottom" height="75" src="http://www.exploratorium.edu/snacks/images/chemistry.gif" width="60" />  <img align="bottom" height="75" src="http://www.exploratorium.edu/snacks/images/fluids.gif" width="60" />  </span></b> </div></div><div class="title"> <b><span style="font-size: large;"> <span style="color: red;"><u>Fog Chamber</u></span></span></b> </div><div class="subtitle"> <b><span style="font-size: large;"> </span></b></div><div class="subtitle"><b><span style="font-size: large;">Make a portable cloud in a bottle. Now you see it; now you don't!</span></b></div><div class="subtitle"><b><span style="font-size: large;"> </span></b> </div><div class="short_description"> <b><span style="font-size: large;">Clouds form when invisible water vapor in the air is cooled enough to form tiny droplets of liquid water. In the atmosphere, this usually happens when moist air cools as it rises to higher altitudes. At higher altitudes the pressure is lower, so that the gas expands, loses internal energy, and cools. You can accomplish the same cooling effect by rapidly expanding the air in a jar. </span></b></div><div class="short_description"><b><span style="font-size: large;"> </span></b> </div><div class="materials_section"><div class="materials_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/materials.gif" width="255" /> </span></b></div><div class="materials"> <ul><li><b><span style="font-size: large;">One 1 gallon (3.S liters) clear glass or plastic jar with a wide mouth <img align="top" border="0" height="1" src="http://www.exploratorium.edu/snacks/images/clear.gif" width="13" />(a pickle jar works well).</span></b></li><li><b><span style="font-size: large;">A rubber glove (Playtex™ brand works well).</span></b></li><li><b><span style="font-size: large;">Matches.</span></b></li><li><b><span style="font-size: large;">Tap water.</span></b></li><li><b><span style="font-size: large;">Adult help.</span></b></li></ul></div></div><div class="assembly_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="23" src="http://www.exploratorium.edu/snacks/images/assembly.gif" width="256" /></span></b> </div><div class="assembly"> <br /><b><span style="font-size: large;">(5 minutes or less)</span></b><br /><br /><b><span style="font-size: large;">Barely cover the bottom of the jar with water. Hang the glove inside the jar with its fingers pointing down, and stretch the glove's open end over the mouth of the jar to seal it.</span></b><br /><br /> </div><div class="to_do_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/tdn.gif" width="256" /></span></b> </div><div class="to_do"> <br /><b><span style="font-size: large;">(15 minutes or more)</span></b><br /><br /><b><span style="font-size: large;">Insert your hand into the glove and pull it quickly outward without disturbing the jar's seal. Nothing will happen. Next, remove the glove, drop a lit match into the jar, and replace the glove. Pull outward on the glove once more. Fog forms inside the jar when you pull the glove outward and disappears when the glove snaps back. The fog will form for 5 to 10 minutes before the smoke particles settle and have to be replenished.</span></b><br /><br /> </div><div class="whats_going_on_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="24" src="http://www.exploratorium.edu/snacks/images/wgo.gif" width="256" /></span></b> </div><div class="whats_going_on"> <br /><b><span style="font-size: large;">Water molecules are present in the air inside the jar, but they are in the form of an invisible gas, or <i>vapor</i>, flying around individually and not sticking to one another. When you pull the glove outward, you allow the air in the jar to expand. In expanding, the air must do work, which means that it loses some of its thermal energy, which in turn means that its molecules (including those of the water vapor), slow down slightly. This is a roundabout way of saying that the air becomes cooler!</span></b><br /><br /><b><span style="font-size: large;">When the water molecules slow down, they can stick to each other more easily, so they begin to bunch up in tiny droplets. The particles of smoke in the jar help this process along: The water molecules bunch together more easily when there is a solid particle to act as a nucleus. When you push the glove back in, you warm the air in the jar slightly, which causes the tiny droplets to evaporate and again become invisible.</span></b><br /><br /><b><span style="font-size: large;">In the atmosphere, air expands as it rises to regions of lower pressure and cools off, forming clouds. This is why clouds often obscure mountain tops. Dust, smoke, and salt particles in the air all provide nuclei that help the droplets condense.</span></b><br /><b><span style="font-size: large;">Meteorologists consider a falling barometer reading (low air pressure) to be a sign of an approaching storm, whereas high pressure is usually a sign of clear weather. The temperature at which water vapor begins to form droplets on a surface is called the <i>dew point.</i></span></b><br /><br /> </div><div class="etcetera_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="16" src="http://www.exploratorium.edu/snacks/images/etcetera.gif" width="256" /></span></b> </div><div class="etcetera"><b><span style="font-size: large;"> </span></b><br /><b><span style="font-size: large;">For an added treat, shine a slide projector through the cloud you make in the jar. When the smoke is fresh, the droplets will be large compared to all wavelengths of visible light, and the light they scatter will be white. As the smoke dissipates, the water drops will become smaller, and the light scattered will create beautiful pastel colors at some viewing angles. Light of different colors diffracts around the small droplets, going off in different directions. If you look at clouds near the sun, you can often see bands of these pastel colors. (Remember, you should never look directly at the sun.)</span></b><br /><br /><b><span style="font-size: large;">For a longer discussion of this effect, see the book <i>Clouds in a Glass of Beer</i>  by C. Bohren (John Wiley & Sons, 1987).</span></b><br /></div></div>

Science Snacks Fog Chamber - Make a portable cloud in a bottle. Now you see it; now you don't!

    Fog Chamber   Make a portable cloud in a bottle. Now you see it; now you don't!   ...

Read more »

Far Out Corners - Your experience of the world influences what you see.

<div dir="ltr" style="text-align: left;" trbidi="on"><b><span style="font-size: large;"><br /></span></b><b><span style="font-size: large;"><br /></span></b><!-- InstanceBeginEditable name="doctitle" --><br /><!-- FACEBOOK OG TAGS --><!-- / FACEBOOK OG TAGS --><!-- InstanceEndEditable --><!-- InstanceBeginEditable name="head" --><!-- InstanceEndEditable --><br /><div class="right_column" style="text-align: center;"><div class="big_illustration"><b><span style="font-size: large;"><img align="bottom" height="181" src="http://www.exploratorium.edu/snacks/far_out_corners/far_out_corners_2_165x181.gif" width="165" /><img align="bottom" height="252" src="http://www.exploratorium.edu/snacks/far_out_corners/far_out_corners_1_196x252.gif" width="196" /></span></b> </div><div class="subjects"> <b><span style="font-size: large;"><img align="bottom" height="75" src="http://www.exploratorium.edu/snacks/images/perception.gif" width="60" /></span></b> </div></div><div class="title"> <b><span style="font-size: large;"> <span style="color: red;"><u>Far Out Corners</u></span></span></b> </div><div class="subtitle"> <b><span style="font-size: large;"> </span></b></div><div class="subtitle"><b><span style="font-size: large;">Your experience of the world influences what you see. </span></b></div><div class="subtitle"><b><span style="font-size: large;"> </span></b> </div><div class="short_description"> <b><span style="font-size: large;">When they first glance at this exhibit, many people say, "What's the big deal? It's just a bunch of boxes." But there are no boxes at all. A closer look reveals that the <i>Far Out Corners</i> exhibit is a cluster of corners lit from below. When you walk past the exhibit with one eye closed, the cubes will seem to turn mysteriously so that they follow your movement. </span></b></div><div class="short_description"><b><span style="font-size: large;"> </span></b> </div><div class="materials_section"><div class="materials_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/materials.gif" width="255" /> </span></b></div><div class="materials"> <ul><li><b><span style="font-size: large;">A large cardboard box <img align="top" border="0" height="1" src="http://www.exploratorium.edu/snacks/images/clear.gif" width="13" />measuring about 19 x 15 inches (48 x 38 cm).</span></b></li><li><b><span style="font-size: large;">Flat black spray paint.</span></b></li><li><b><span style="font-size: large;">Thick, white, nonflexible posterboard measuring at least 15 x 15 inches (38 x 38 cm).</span></b></li><li><b><span style="font-size: large;">X-Acto™ knife or matte knife.</span></b></li><li><b><span style="font-size: large;">Masking tape or transparent tape.</span></b></li><li><b><span style="font-size: large;">A bright free-standing lamp.</span></b></li><li><b><span style="font-size: large;">Adult help.</span></b></li></ul></div></div><div class="assembly_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="23" src="http://www.exploratorium.edu/snacks/images/assembly.gif" width="256" /></span></b> </div><div class="assembly"> <b><span style="font-size: large;"><img align="right" border="0" height="114" src="http://www.exploratorium.edu/snacks/far_out_corners/far_out_corners_3_325x114.gif" width="325" /></span></b><br /><br /><b><span style="font-size: large;">(1 hour or less) You can cut the inside corners from square-cornered containers, such as clean milk cartons or tissue boxes, or you can make your own corners from posterboard. To make your own, use an X-Acto™ knife or matte knife to cut the posterboard into nine squares, each of which measures 5 x 5 inches (13 x 13 cm).</span></b><br /><b><span style="font-size: large;">Now use three of the squares to construct a partial cube or corner in the following fashion: Tape two squares together at one edge; open each of the two squares into a right angle; tape the third square on top of the first two squares. Make three partial cubes, or corners.</span></b><br /><br /><b><span style="font-size: large;"><img align="bottom" border="0" height="84" src="http://www.exploratorium.edu/snacks/far_out_corners/far_out_corners_4_344x84.gif" width="344" /></span></b> <b><span style="font-size: large;"><img align="left" border="0" height="148" src="http://www.exploratorium.edu/snacks/far_out_corners/far_out_corners_5_166x148.gif" width="166" /></span></b><br /><br /><b><span style="font-size: large;">Spray-paint the inside of the large cardboard box black. When the box is dry, arrange the corners so that two are side by side on the bottom of the box, as shown. Make sure the hollow open sides of each corner are facing out toward you and down. Tape them so they are tilted up at a small angle. Place the third corner as far forward as possible on top of the original two, also tilted upward. Tape all three corners in place. Now position the light so that it shines directly into the box.</span></b><br /><br /> </div><div class="to_do_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/tdn.gif" width="256" /></span></b> </div><div class="to_do"> <br /><b><span style="font-size: large;">(15 minutes or more)Stand back ten feet and close one eye. With a little mental effort, you can see the corners that you have constructed as three-dimensional cubes rather than hollow corners.</span></b><br /><br /><b><span style="font-size: large;">Walk back and forth parallel to the box. Notice that the cube on top seems to be following you as you move.</span></b><br /><br /> </div><div class="whats_going_on_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="24" src="http://www.exploratorium.edu/snacks/images/wgo.gif" width="256" /></span></b> </div><div class="whats_going_on"> <br /><b><span style="font-size: large;">The first step to successfully seeing the top partial cube turn with you lies in your ability to perceive it as a complete six-sided figure. This perception has a lot to do with being raised in a society that recognizes cubes as a common shape. Your brain is used to seeing cubes, so it fills in the rest of the cube shape, even though this partial cube only has three sides.</span></b><br /><br /><b><span style="font-size: large;">As you move past the exhibit, your view of the corners changes in a way that would not make any sense if the corners were stationary cubes. Your eye-brain system is used to seeing things that are near you move faster than things that are farther away. When you are riding in a car, for example, nearby objects seem to whiz by, whereas distant objects seem to follow you at a slower pace. Since you perceive this inside corner to be the outside of a solid cube, your brain "sees" the corner farthest from you as being the closest. To maintain this misconception, your brain perceives a rapid rotation of the cube as your angle to the corner changes.</span></b><br /><br /><b><span style="font-size: large;"><img align="bottom" border="0" height="98" src="http://www.exploratorium.edu/snacks/far_out_corners/far_out_corners_6_312x98.gif" width="312" /></span></b> <br /><b><span style="font-size: large;">The diagram above shows how this illusion works. In the real situation, as your eye moves to the right, it sees more of side A. In order to see more of side A of the imagined corner, the perceived cube must be seen to rotate as you move.</span></b><br /><b><span style="font-size: large;"> </span></b></div><div class="whats_going_on"><b><span style="font-size: large;"> </span></b></div></div>

Science Snacks Far Out Corners - Your experience of the world influences what you see.

Far Out Corners   Your experience of the world influences what you see.    When they first glanc...

Read more »

Falling Feather - Prove to yourself that Galileo was right!

<div dir="ltr" style="text-align: left;" trbidi="on"><div style="text-align: center;"><b><span style="font-size: large;"><br /></span></b></div><div style="text-align: center;"><b><span style="font-size: large;"><br /></span></b></div><div style="text-align: center;"><!-- InstanceBeginEditable name="doctitle" --></div><!-- FACEBOOK OG TAGS --><!-- / FACEBOOK OG TAGS --><!-- InstanceEndEditable --><!-- InstanceBeginEditable name="head" --><!-- InstanceEndEditable --><br /><div class="right_column" style="text-align: center;"><div class="big_illustration"><b><span style="font-size: large;"><img align="bottom" src="http://www.exploratorium.edu/snacks/falling_feather/falling_feather_1_231x231.gif" /></span></b> </div><div class="subjects"> <span style="color: red;"><u><b><span style="font-size: large;"><img align="bottom" height="75" src="http://www.exploratorium.edu/snacks/images/mechanics.gif" width="60" /></span></b> </u></span></div></div><div class="title"><span style="color: red;"><u> <b><span style="font-size: large;"> Falling Feather</span></b></u></span> </div><div class="subtitle"> <b><span style="font-size: large;"> </span></b></div><div class="subtitle"><b><span style="font-size: large;">Prove to yourself that Galileo was right! </span></b></div><div class="subtitle"><b><span style="font-size: large;"> </span></b> </div><div class="short_description"> <b><span style="font-size: large;">In a famous demonstration, Galileo supposedly dropped a heavy weight and a light weight from the top of the Leaning Tower of Pisa to show that both weights fall at the same acceleration. Actually, this rule is true only if there is no air resistance. This demonstration lets you repeat Galileo's experiment in a vacuum. </span></b></div><div class="short_description"><b><span style="font-size: large;"> </span></b> </div><div class="materials_section"><div class="materials_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/materials.gif" width="255" /> </span></b></div><div class="materials"> <ul><li><b><span style="font-size: large;">A clear, plastic, rigid-walled tube <img align="top" border="0" height="1" src="http://www.exploratorium.edu/snacks/images/clear.gif" width="13" /> with at least a 1 inch (2.5 cm) inner diameter and at least 3 feet (90 cm) long. Available at your local plastic store. (Longer tubes show the effect more clearly.)</span></b></li><li><b><span style="font-size: large;">A solid rubber stopper and a one-hole rubber stopper to fit in the ends of the plastic tube.</span></b></li><li><b><span style="font-size: large;">A section of copper tubing about 4 inches (10 cm) long that fits tightly in the hole in the rubber stopper (glass tubing can be used if care is taken).</span></b></li><li><b><span style="font-size: large;">A thick-walled flexible plastic or rubber vacuum tubing about 6 feet (180 cm) long.</span></b></li><li><b><span style="font-size: large;">A coin and a feather (or a small piece of paper).</span></b></li><li><b><span style="font-size: large;">A vacuum pump (use a regular lab vacuum pump if available; if not, use a small hand pump such as Mityvac®).</span></b></li><li><b><span style="font-size: large;">2 hose clamps.</span></b></li><li><b><span style="font-size: large;">Adult help.</span></b></li></ul></div></div><div class="assembly_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="23" src="http://www.exploratorium.edu/snacks/images/assembly.gif" width="256" /></span></b> </div><div class="assembly"> <b><span style="font-size: large;"><img align="right" border="0" height="171" src="http://www.exploratorium.edu/snacks/falling_feather/falling_feather_2_340x171.gif" width="340" /></span></b><br /><br /><b><span style="font-size: large;">(30 minutes or less)</span></b><br /><br /><b><span style="font-size: large;">Insert the solid stopper firmly into one end of the plastic tube. Put the coin and feather in the tube. Push the copper tube through the one-hole stopper, and firmly insert the stopper in the other end of the plastic tube. Push the vacuum tubing over the copper tube and secure it with a hose clamp, if needed. Attach the other end of the vacuum tubing to the pump; again, use a hose clamp if needed.</span></b><br /><br /> </div><div class="to_do_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/tdn.gif" width="256" /></span></b> </div><div class="to_do"> <br /><b><span style="font-size: large;">(15 minutes or more)</span></b><br /><br /><b><span style="font-size: large;">Invert the tube and let the objects fall. Notice that the feather falls much more slowly than the coin. Now pump the air out of the tube and invert it again (the pump can remain attached while you invert the tube). Notice that the feather falls much more rapidly than before - in fact, it falls almost as fast as the coin. Let the air back into the tube and repeat the experiment. (Try to avoid rubbing the wall of the tube; otherwise, static electricity may make the feather stick to it.)</span></b><br /><br /> </div><div class="whats_going_on_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="24" src="http://www.exploratorium.edu/snacks/images/wgo.gif" width="256" /></span></b> </div><div class="whats_going_on"> <br /><b><span style="font-size: large;">Galileo predicted that heavy objects and light ones would fall at the same rate. The reason for this is simple. Suppose the coin has 50 times as much mass as the feather. This means that the earth pulls 50 times as hard on the coin as it does on the feather. You might think this would cause the coin to fall faster. But because of the coin's greater mass, it's also much harder to accelerate the coin than the feather - 50 times harder, in fact! The two effects exactly cancel out, and the two objects therefore fall with the same acceleration.</span></b><br /><br /><b><span style="font-size: large;">This rule holds true only if gravity is the only force acting on the two objects. If the objects fall in air, then air resistance must also be taken into account. Larger objects experience more air resistance. Also, the faster an object is falling, the more air resistance it feels. When the retarding force of the air just balances the downward pull of gravity, the object will no longer gain speed; it will have reached what is called its <i>terminal velocity</i>. Since the feather is so much lighter than the coin, the air resistance on it very quickly builds up to equal the pull of gravity. After that, the feather gains no more speed, but just drifts slowly downward. The heavier coin, meanwhile, must fall much longer before it gathers enough speed so that air resistance will balance the gravitational force on it. The coin quickly pulls away from the feather.</span></b><br /><br /> </div><div class="etcetera_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="16" src="http://www.exploratorium.edu/snacks/images/etcetera.gif" width="256" /></span></b> </div><div class="etcetera"> <div class="etcetera"><br /></div><div class="etcetera"><b><span style="font-size: large;">The terminal velocity of a falling human being with arms and legs outstretched is about 120 miles per hour (192 km per hour) - slower than a lead balloon, but a good deal faster than a feather!</span></b></div><div class="etcetera"><br /></div></div></div>

Science Snacks Falling Feather - Prove to yourself that Galileo was right!

Falling Feather   Prove to yourself that Galileo was right!    In a famous demonstration, Galileo supp...

Read more »

Fading Dot - Now you see it; now you don't. An object without a sharp edge can fade from your view

<div dir="ltr" style="text-align: left;" trbidi="on"><b><span style="font-size: large;"><br /></span></b><div style="text-align: center;"><b><span style="font-size: large;"><br /></span></b></div><div style="text-align: center;"><!-- InstanceBeginEditable name="doctitle" --></div><!-- FACEBOOK OG TAGS --><!-- / FACEBOOK OG TAGS --><!-- InstanceEndEditable --><!-- InstanceBeginEditable name="head" --><!-- InstanceEndEditable --><br /><div class="right_column" style="text-align: center;"><div class="big_illustration"><b><span style="font-size: large;"><img align="bottom" height="285" src="http://www.exploratorium.edu/snacks/fading_dot/fading_dot_1_228x163.gif" width="400" /></span></b> </div><div class="subjects"> <span style="color: red;"><u><b><span style="font-size: large;"><img align="bottom" height="75" src="http://www.exploratorium.edu/snacks/images/perception.gif" width="60" /></span></b> </u></span></div></div><div class="title"><span style="color: red;"><u> <b><span style="font-size: large;"> Fading Dot</span></b></u></span> </div><div class="subtitle"> <b><span style="font-size: large;"> </span></b></div><div class="subtitle"><b><span style="font-size: large;">Now you see it; now you don't. An object without a sharp edge can fade from your view. </span></b></div><div class="subtitle"><b><span style="font-size: large;"> </span></b> </div><div class="short_description"> <b><span style="font-size: large;">A fuzzy, colored dot that has no distinct edges seems to disappear. As you stare at the dot, its color appears to blend with the colors surrounding it. </span></b></div><div class="short_description"><b><span style="font-size: large;"> </span></b> </div><div class="materials_section"><div class="materials_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/materials.gif" width="255" /> </span></b></div><div class="materials"> <ul><li><b><span style="font-size: large;">Pink paper <img align="top" border="0" height="1" src="http://www.exploratorium.edu/snacks/images/clear.gif" width="13" />(1 sheet).</span></b></li><li><b><span style="font-size: large;">Blue paper dot (about 1 inch [2.5 cm] in diameter).</span></b></li><li><b><span style="font-size: large;">Waxed paper.</span></b></li></ul></div></div><div class="assembly_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="23" src="http://www.exploratorium.edu/snacks/images/assembly.gif" width="256" /></span></b> </div><div class="assembly"> <br /><b><span style="font-size: large;">(5 minutes or less)</span></b><br /><br /><b><span style="font-size: large;">Use the blue paper to make a 1 inch (2.5 cm) dot, and place the dot in the center of the pink paper. Cover the paper with a sheet of waxed paper. Look through the waxed paper at the colored papers below. Lift the waxed paper from the pink paper until you see very faint blue color in a field of pale pink.</span></b><br /><br /> </div><div class="to_do_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="19" src="http://www.exploratorium.edu/snacks/images/tdn.gif" width="256" /></span></b> </div><div class="to_do"> <br /><b><span style="font-size: large;">(15 minutes or more)</span></b><br /><br /><b><span style="font-size: large;">Stare at a point next to the fuzzy dot for a while without moving your eyes or your head. The blue will gradually fade into the field of pink. As soon as you move your head or eyes, notice that the dot reappears. Experiment with other color combinations.</span></b><br /><br /> </div><div class="whats_going_on_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="24" src="http://www.exploratorium.edu/snacks/images/wgo.gif" width="256" /></span></b> </div><div class="whats_going_on"> <br /><b><span style="font-size: large;">Even though you are not aware of it, your eyes are always making tiny jittering movements. Each time your eyes move, they receive new information and send it to your brain. You need this constant new information to see images.</span></b><br /><br /><b><span style="font-size: large;">Your eyes also jitter when you look at this dot, but the color changes at the edge of the dot (as seen fuzzily through the waxed paper) are so gradual that your eyes can't tell the difference between one point on the dot and a point right next to it. Your eyes receive no new information, and the image seems to fade away. If the dot had a distinct border, your eyes would immediately detect the change when they jittered, and you would continue to see the dot.</span></b><br /><br /><b><span style="font-size: large;">You may have noticed that, although the dot fades, just about everything else in your field of vision remains clear. That's because everything else you see has distinct edges.</span></b><br /><br /> </div><div class="etcetera_header"><b><span style="font-size: large;"><img align="bottom" border="0" height="16" src="http://www.exploratorium.edu/snacks/images/etcetera.gif" width="256" /></span></b> </div><div class="etcetera"> <div class="etcetera"><br /></div><div class="etcetera"><b><span style="font-size: large;">For more information, we suggest you read the sections on lateral inhibition and chromatic lateral inhibition in <i>Seeing the Light</i>, by David Falk, Dieter Brill, and David Stork (Harper & Row, 1986).</span></b></div><div class="etcetera"><br /></div><div class="etcetera"><br /></div></div></div>

Science Snacks Fading Dot - Now you see it; now you don't. An object without a sharp edge can fade from your view

Fading Dot   Now you see it; now you don't. An object without a sharp edge can fade from your vi...

Read more »