Think of all the wonderful sensations taste can impart to us – the delicious Thanksgiving turkey and gravy, mashed potatoes, cranberry sauce and pumpkin pie! Coffee, chocolate, lush strawberries – the list goes on and on! Receptors on our tongues bind to chemicals in our food and relay the information about the chemicals to our brain. Surprisingly, all those wonderful tastes are transmitted to our brains through only four types of receptors on our tongues – those for sweet, sour, salt and bitter. How can this be so?

No assembly needed

Have students work in pairs. One student closes their eyes and holds their nose, while another feeds them a lifesaver, without telling them the flavor. The student should try to guess what flavor the life saver is, without letting go of their nose. Observations should proceed for a minute or so as the candy dissolves in their mouth. Is there any change in the taste of the candy from the beginning to the end of the experiment? Describe the tastes.

A series of slits moving rapidly past your eye allows you to see images in short bursts. Such rapid but fragmented views of moving objects can make the objects appear to jerk along, change speed, or even move backward.

(30 minutes or less)

Print out the stroboscope pattern provided on a separate screen here. Enlarge it if you wish. Cut out the pattern and glue it to the posterboard.

Cut the posterboard to the same shape as the stroboscope, including the slits. You can cut with a good pair of scissors alone, or use scissors in combination with a utility knife.

Mount the stroboscope disk on the rotator. You can use adhesive Velcro™ to mount the disk to the electric drill or other device. If you use a drill with a chuck, you can use a bolt as a shaft, with two nuts to hold the disk. (You can also make a simple manual rotator by simply sticking the pushpin through the center of the disk and into the end of a pencil or wooden dowel.)

(15 minutes or more)

Close one eye. Hold the stroboscope so that the side with the horses is facing away from you, and so that you can see through a slit with your open eye. Spin the disk and look through the slits at your surroundings. Notice that you can see the entire scene on the other side of the disk, not just one small strip of it.

Try spinning the disk faster, then slower, and compare the results.

Have a friend hold a hand so that you can see it through the spinning disk. Ask your friend to move his or her hand from side to side. Notice that the movement you see is jerky rather than smooth. Have your friend move his or her hand rapidly, and then slowly. Notice that the amount of jerkiness changes as the speed of the hand movement changes.

Stand facing a mirror, and hold the disk and rotator in front of you. Be sure the disk is mounted on the rotator so that the horses are facing the mirror. Spin the disk and watch its reflection in the mirror through one of the slits. Concentrate your attention on one of the horses, and you will see it gallop!

Let water run slowly enough to produce a stream that breaks up into separate droplets as it falls. Place a black background behind the well-illuminated drops of water. Look through the spinning stroboscope and watch the water-droplets fall in slow motion. Vary the stroboscope’s speed and see if you can make the water-droplets stand still or even look as if they are moving upward.

As the strobe disk rotates, a series of open slits moves rapidly past your eye. Each time a slit passes your eye, you see a glimpse of the scene on the far side of the disk. Each open-slit image lingers in your eye and brain long enough to merge with the next image. This phenomenon, called persistence of vision, can combine the glimpses in such a way that your brain sees continuous motion.

If an object in the scene moves, your eye and brain can draw incorrect conclusions about that object’s motion. When you look at the stream of water, for example, one slit allows you to view a droplet in a particular position. Depending on how fast your strobe is turning, the next slit might let you see a different droplet just slightly below the position of the one previously viewed. Your eye-brain system interprets the combined views as the slow motion of a single droplet. If the second view catches the droplet in a position just above that of the previous view, the droplet will seem to rise.

A simple stack of blocks demonstrates that an object at rest will remain at rest, unless a force causes it to move.

• 5 or 6 wooden blocks, each about 13 cm (5 in.) long, cut from a relatively smooth-surfaced two-by-four
• meter stick

1. Stack the blocks neatly with the large sides parallel to tabletop.2. Use the meter stick or other suitable “whacker” to rapidly whack back and forth just above the tabletop. With each whack, knock another block out from the bottom of the stack. Caution: Blocks will go flying, so make sure nobody is standing where they might get hit!

3. Notice that when the bottom block is whacked out of the stack, the rest of the stack essentially drops straight down.

When the bottom block is knocked away by the “whacker” force, the rest of the stack resists moving horizontally along with it. This is due to a phenomenon called inertia – a resistance to change in motion. Inertia is the subject of Isaac Newton’s first law of motion: An object remains at rest, or in uniform motion in a straight line, unless it’s forced to change its state of motion by forces acting upon it.

Mass is a measure of inertia, as shown in Newton’s second law: Force = mass x acceleration. In other words, the more massive something is, the harder you have to push or pull it to change its state of motion. The stack of blocks is fairly massive, so it has quite a bit of inertia.

You may notice, though, that the stack moves horizontally just a bit, especially as the stack gets smaller and therefore has less inertia. That’s because there’s a frictional force between the bottom block and the stack above it. If we could turn friction off, the stack wouldn’t move sideways at all.

In the 1700s, spherical glass bottles filled with water were used to focus candlelight for fine work such as lace making. Round bottles of water, left in an open window, have been known to start fires by focusing sunlight into an intense “hot spot.”

(1 minute or less)

Fill the flask or fishbowl with water to make a water sphere lens.

(15 minutes or more)

Place the light source (the lightbulb or the candle) more than 1 foot (30 cm) from the water sphere lens. Hold the white card against the side of the lens opposite the light source. Move the card away from the sphere until you see an image of the filament (or flame) on the card. Notice that the image is inverted.

Move the light source up and notice that its image moves down.

Move the light very close to the water sphere, and notice that you cannot find an image on the card at any distance.

Look through the water sphere lens at a newspaper held close to the other side of the sphere. Notice that the sphere acts as a magnifying glass. Vary the light-to-lens distance and notice how the image-to-lens distance changes. Also notice how the image changes size.

Light rays from the bulb or candle bend when they enter the water-filled sphere, and bend again when they leave the sphere, as shown in the diagram below. The only light rays that don’t bend are the ones that enter the sphere at a straight-on, 90-degree angle – that is, the ones that pass through the center of the bowl.

The sphere acts just like a lens, focusing the light that passes through into an image on the other side. The image must lie on a straight line from the object through the center of the lens.

The image is upside down and reversed right to left. The motion of the image is also reversed: When the object moves up, the image moves down; when the object moves closer to the sphere, the image moves farther away. It might help to picture a seesaw: When one side moves up, the other side moves down.

Every lens has a focal point, which is a spot where light rays from far away converge after passing through the lens. The distance from the center of the lens to the focal point is called the focal length. Measure the focal length of your lens by finding a bright light source that’s more than 30 feet (9 m) away. Using the white card, find the distance from the lens to the image. This is the focal length. If you use the sun as your light source, the focused sunlight may be hot enough to burn the paper card. Be careful!

If an object is closer than one focal length to the center of the water sphere lens, the lens can’t bend the light rays from the object enough to bring them back together to form an image. However, when you look through the water sphere lens at a nearby object, the lens of your eye can complete the bending, forming an image on your retina. The image on your retina made with the help of the water sphere lens is larger than the largest image you could make with your eye alone. The water sphere lens is thus a magnifying glass.

Water forms a spiraling, funnel-shaped vortex as it drains from a 2-liter soda bottle. A simple connector device allows the water to drain into a second bottle. The whole assembly can then be inverted and the process repeated.

(5 minutes or less with the Tornado Tube™; 15 minutes or less with the washer and electrical tape)

Fill one of the soda bottles about two-thirds full of water. For effect, you can add a little food coloring or paper bits to the water. Screw the bottles onto both ends of the plastic connector. (CAUTION: Do not screw the connector on too tightly!) Or tape the bottles together with the washer between them.

(15 minutes or more)

Place the two bottles on a table with the filled bottle on top. Watch the water slowly drip down into the lower bottle as air simultaneously bubbles up into the top bottle. The flow of water may come to a complete stop.

With the filled bottle on top, rapidly rotate the bottles in a circle a few times. Place the assembly on a table. Observe the formation of a funnel-shaped vortex as the bottle drains.

Notice the shape of the vortex. Also, notice the flow of the water as it empties into the lower bottle.

You can make the vortex with a single bottle by twirling the bottle and holding it over a water basin or the ground to drain, but you lose the water and have to refill the bottle each time you use it.

When the water is not rotating, surface tension creates a skinlike layer of water across the small hole in the center of the connector.

If the top bottle is full, the water can push out a bulge in this surface to form a bulbous drop, which then drips into the lower bottle. As water drops into the lower bottle, the pressure in the lower bottle builds until air bubbles are forced into the upper bottle. The pressure that the water exerts on the surface in the connector decreases as the water level in the upper bottle drops. When the water level and pressure drop low enough, the water surface can hold back the water and stop the flow completely.

If you spin the bottles around a few times, the water in the upper bottle starts rotating. As the water drains into the lower bottle, a vortex forms. The water is pulled down and forced toward the drain hole in the center by gravity. If we ignore the small friction forces, the angular momentum of the water stays the same as it moves inward. This means that the speed of the water around the center increases as it approaches the center of the bottle. (This is the same reason that the speed of rotating ice skaters increases when they pull in their arms.)

To make water move in a circle, forces called centripetal forces must act on the water. These “center pulling” forces are provided by a combination of air pressure, water pressure, and gravity.

You can tell where the centripetal forces are greater by looking at the slope of the water. Where the water is steeper, such as at the bottom of the vortex, the centripetal force on the water is greater. Water moving with higher speeds and in smaller radius curves requires larger forces. The water at the bottom of the vortex is doing just this, and so the wall of the vortex is steepest at the bottom. (Think about race cars: Racetracks have steeper banks on high-speed, sharp corners to hold the cars in their circular paths around the track.)

The hole in the vortex allows air from the lower bottle to flow easily into the upper bottle. This enables the upper bottle to drain smoothly and completely.

A bob, or mass, hangs from a string attached to the front of the walking men. Watch as the string almost draws the vectors that make the toy work.

No assembly needed.

a) Have students hang the mass over the side of a desk and let the toy walk. Resist the temptation to stop the toy when it gets to the edge! Why doesn’t it fall off? How does it “know” when to stop?

b) Remove the mass from the front of the toy. Place the toy on the board. Raise the board to an angle that just causes the toy to walk down the ramp. Use the angle of the ramp and the mass of the toy to calculate how much weight would have to be attached to the string to get it to move forward.

Your brain gets used to seeing familiar things in certain ways. When the brain receives a strange view of a familiar object, the consequences can be intriguing. In the Exploratorium exhibit titled “Vanna,” two pictures of the face of TV personality Vanna White seem identical when viewed upside down, but exhibit a bizarre difference when viewed right-side up.

(15 minutes or less)

Cut two pieces of posterboard to the size of the pictures you cut out. If you are using a magazine cover, you can use the whole cover or you can trim off the title. It is not necessary to trim the picture to the outline of the person.

Glue the first picture to a piece of posterboard.

Cut the eyes and mouth from the second picture. Turn them upside down and glue them over the eyes and mouth of the third picture. Glue this picture to a piece of posterboard.

(5 minutes or more)

Place both pictures upside down before letting anyone view them. Then have the viewers look at the two upside-down pictures. Finally, have the viewers look at both pictures rightside up.

Your viewers may or may not recognize the personality in your picture when the picture is upside down. The two upside-down views may look strange (one perhaps stranger than the other); but turn them right-side up and one looks normal, while the other may look grotesque.

Since an upside-down face is not a familiar point of view, your viewers may not have noticed that one of the pictures has been altered. It’s only when the photos are turned right-side up, and the view is more familiar, that you notice the real difference.

In the Exploratorium’s Touch the Spring exhibit, a spring is placed in front of a concave mirror. The actual spring is not visible to the viewer, but the viewer can see the mirror image of the spring formed in space. When you try to touch the spring, you are attempting to touch an image. Your hand moves right through what seems to be a solid object! This is a magician’s illusion at its finest. Here, we substitute a lightbulb for the spring.

(1 hour or less)

Make a small wooden box with one open side as shown in the drawing. The height of the box should be slightly less than half the height of the mirror, and it should be wide enough and deep enough to hold the light bulb. Paint all surfaces of the box black.

Mount the socket that has no electrical cord or plug so that it is centered on top of the box. Mount the other socket (the one with the cord and plug) upside-down inside the box, directly beneath the empty socket, as shown in the drawing.

Build the mirror support as shown in the drawing, and place the mirror in it.

(30 minutes or more)

Plug in the lightbulb and place the box with its open side facing the mirror. To find the focal length of the mirror, place the mirror far from the lightbulb – at least 20 feet (6 m) – so that its concave (hollow) side is facing the lightbulb. The mirror will then make a real image of the lightbulb close to the focal point of the mirror. Find the distance from the center of the mirror to the image of the lightbulb, and you will find the focal length of the mirror.

To find the location of the image, take a 3 x 5 inch (8 x 13 cm) card and hold it near the center of – and touching – the surface of the mirror. Move the card slowly away from the mirror. When the image of the bulb is in sharp focus, the card is near the focal point.

Place the mirror two focal lengths from the lightbulb. The concave mirror will reflect an image of the glowing bulb. This image will appear in space in front of the mirror. By carefully adjusting the vertical and horizontal position of the box, you can position the image so that it appears to be in the empty socket on top of the box. (You may have to place magazines or books under the box to adjust its height.)

The illusion works best in a darkened room. Have people stand back about 15 feet (5 m) so that they see a bulb in the upper socket. Then have them move slowly toward the bulb. They may have to bend or straighten slightly or move right or left slightly to maintain an undistorted image. When they are about 6 feet (2 m) from the image of the bulb, pass your hand through it. The illusion of your hand passing right through a lightbulb is impressive, even when everything is out in the open.

In the Exploratorium exhibit, everything is inside a large cabinet. To touch the image, you must reach through a small opening. The cabinet hides all the clues and enhances the illusion, but is a more elaborate construction project with associated storage problems.

The image you see is formed by the concave spherical mirror. Light rays spreading out from one point on the lightbulb are reflected by the concave mirror so that they come back together at a point in space – creating a real image of that point.

The rays continue on through this convergence point and strike your eye. The lens of your eye brings the rays together once again to create an image on your retina. Your eye and brain can’t tell the difference between a retinal image of the reflected bulb and a retinal image of the actual bulb.

In some respects, however, the reflected image of the lightbulb differs from the actual bulb. Placing an object behind the reflected image will obscure the lightbulb. Many people feel queasy when they see this seemingly unnatural occurrence.

By measuring the amount of surface each tire presses onto the ground and the pressure inside each tire, you can calculate the weight of a car.

(This activity is not in metric since most common tire pressure gauges are in PSI or Pounds per Square Inch. A metric conversion can me made at the end if necessary.)

No assembly needed.

You need to measure the surface area of the bottom of each tire. This “footprint” can be found by shoving pieces of cardboard against the base of each wheel. Remember to set the parking brake while taking these measurements.

1) Most tire footprints will be roughly rectangular in shape. To find the length and width of this footprint, use thin cardboard to define each tire’s footprint boundary. Shove the cardboard under the tire as tightly as possible to border each edge of the footprint.

Shove the cardboard under the tire in all four directions.2) Roll the car off from the cardboard and measure the area bounded by the cardboard. Take measurements in inches.

3) Use a tire gauge to measure the internal air pressure of the tire.

4) Find the amount of tire surface area touching the ground. To find this, multiply the length and width of the “footprint.” Your answer should be in square inches.

5) To find the amount of weight the tire holds, multiply the surface area by the psi in that tire.
When you multiply square inches by pounds per square inch, the square inches cancel and you’re left with pounds.

Example:

6) Repeat these steps for all other tires.

7) Add the weight together for all four tires – that’s the total weight of the car.

To see how close you came to the real weight of the car, check the owner’s manual or look at the specification plate on the inside of the driver’s side door.

All of a car’s weight is spread among each of the four tires. The weight on each tire is spread among it’s footprint.

Closing one eye eliminates one of the clues that your brain uses to judge depth. Trying to perform a simple task with one eye closed demonstrates how much you rely on your depth perception

(5 minutes or less)

Stand the washer on its side, using the lump of clay to support it so that the edge of the washer – not the hole – is facing you.

(5 minutes or more)

Stand far enough from the washer so that you must extend your arm to reach it. Now close one eye and try to put the dowel through the hole in the washer.

Open both eyes and try again.

One of the clues that your brain uses to judge distance and depth is the very slight difference between what your left eye sees and what your right eye sees. Your brain combines these two views to make a three-dimensional picture of the world.

Try this experiment again with one eye closed. But this time, move your head from side to side as you “thread the needle.” People who have lost an eye can learn to perceive depth by comparing the different views they obtain from one eye at two separate times.