Solar Still

Contributed by Eva Johnson, Watershed School, Boulder, Colorado, USA.

 fig 1: Rough Dimension sketch

Materials Required

Five 1/2" PVC pipes each cut to 16 inches. Two 1/2" PVC pipes each cut to 24 inches. Four 2-ended PVC connectors. Two 3-ended PVC connectors. A 2ft. by 4ft. transparent tarp (plastic sheet). A 2ft. by 3ft. transparent tarp (plastic sheet). Duct tape

Construction Method

The Still is built with 1/2" PVC piping (two 18" sides, two 24" sides) with one of the 18" sides built up 16" taking a right angle shape. (connected with PVC connectors) The bottom PVC pipes are cut to act like gutters. A transparent plastic tarp stretches from the bottom of the tall side up over and down across to the low end, making a slope in the tarp. Because this is a cheap project, duct tape is used to attach the tarp. One corner of the base is risen so it's taller than the others, making the opposite corner the lowest. At the lowest corner, a hole is drilled underneath in the PVC connector, so if water was to fall into the gutters, by gravity it would flow down to the lowest end and run out of the hole.Underneath the whole still, another tarp is laid down to hold the unpure water that will soon be evaporated.

So if a person was to pour some of the dirty water from a river underneath the solar still, sunlight would heat the still and cause the water to evaporate. Once evaporated, the water will hit the top and sides of the tarp and drip down into the gutters. Because

the frame of the still is slanted, the water in the gutters will flow down to the bottom corner and out the hole where it can be collected and used

 

    

fig 2: side view of Still                                                  fig 3: Back view of still

fig 4: Front view of Still

Toothpaste Tube PumpThis pump is just like the Jerk Pump. The onlydifference is that the materials used, both for thepipe and the valve are very different.1.Old toothpaste tubes are not for throwing.Take a tube and cut it 2-cm from the mouth end.Clean it up. With a nail make a hole in the tubenear the crimped base.2. Cut a balloon about 2.5-cm from the mouthend. Stretch the mouth of the cut balloon andslide it on the threaded end of the mouth of thetube. This makes a very efficient valve.3. Insert this valve end in the big toothpaste tubeas shown. Also insert a plastic straw (a Frootistraw or an old refill) in the hole near the crimpedend. The cut balloon allows flow of water in onedirection. Water can enter the tube from belowbut cannot come out from that end. The cutballoon is a very efficient valve.4. Hold the tube with your hand and move it upand down into a mug of water. After a couple ofstrokes water will start squirting out.

Toothpaste Pump

Straw Centrifuge

Simple Electric Motor Energy comes in many forms. Electric energy can be converted into useful work, or mechanical energy, by machines called electric motors. Electric motors work due to

electromagnetic interactions: the interaction of current (the flow of electrons) and a magnetic field.

Materials D battery Insulated 22G wire 2 large-eyed, long, metal sewing needles (the eyes must be large enough to fit

the wire through) Modeling clay Electrical tape Hobby knife Small circular magnet Thin marker

Procedure1. Starting in the center of the wire, wrap the wire tightly and neatly around the

marker 30 times.2. Slide the coil you made off of the marker.3. Wrap each loose end of the wire around the coil a few times to hold it

together, then point the wires away from the loop, as shown:

What is this? What is its purpose?

4. Ask an adult to use the hobby knife to help you remove the top-half of the wire insulation on each free end of the coil. The exposed wire should be facing the same direction on both sides. Why do you think half of the wire needs to remain insulated?

5. Thread each loose end of the wire coil through the large eye of a needle. Try to keep the coil as straight as possible without bending the wire ends.

6. Lay the D battery sideways on a flat surface.7. Stick some modeling clay on either side of the battery so it does not roll away.8. Take 2 small balls of modeling clay and cover the sharp ends of the needle.9. Place the needles upright next to the terminals of each battery so that the side

of each needle touches one terminal of the battery.

10. Use electrical tape to secure the needles to the ends of the battery. Your coil should be hanging above the battery.

11. Tape the small magnet to the side of the battery so that it is centered underneath the coil.

12. Give your coil a spin. What happens? What happens when you spin the coil in the other direction? What would happen with a bigger magnet? A bigger battery? Thicker wire?

Results

The motor will continue to spin when pushed in the right direction. The motor will not spin when the initial push is in the opposite direction.

Why?

The metal, needles, and wire created a closed loop circuit that can carry current. Current flows from the negative terminal of the battery, through the circuit, and to the positive terminal of the battery. Current in a closed loop also creates its own magnetic field, which you can determine by the “Right Hand Rule.” Making a “thumbs up” sign with your right hand, the thumb points in the direction of the current, and the curve of the fingers show which way the magnetic field is oriented.

In our case, current travels through the coil you created, which is called the armature of the motor. This current induces a magnetic field in the coil, which helps explain why the coil spins.

Magnets have two poles, north and south. North-south interactions stick together, and north-north and south-south interactions repel each other. Because the magnetic field created by the current in the wire is not perpendicular to the magnet taped to the

battery, at least some part of the wire’s magnetic field will repel and cause the coil to continue to spin.

So why did we need to remove the insulation from only one side of each wire? We need a way to periodically break the circuit so that it pulses on and off in time with the rotation of the coil. Otherwise, the copper coil’s magnetic field would align with the magnet’s magnetic field and stop moving because both fields would attract each other. The way we set up our engine makes it so that whenever current is moving through the coil (giving it a magnetic field), the coil is in a good position to be repelled by the stationary magnet’s magnetic field. Whenever the coil isn’t being actively repelled (during those split second intervals where the circuit is switched off), momentum carries it around until it’s in the right position to complete the circuit, induce a new magnetic field, and be repelled by the stationary magnet again.

Once moving, the coil can continue to spin until the battery is dead. The reason that the magnet only spins in one direction is because spinning in the wrong direction will not cause the magnetic fields to repel each other, but attract.

Plane Mirror Reflection ExperimentPlane (flat) mirrors have a reflective surface that bounces back light within 180 degrees of the mirror's face. We use these mirrors every day in our bathrooms, bedrooms, and cars. When you look in a plane mirror, you see a mirror imagethat is flipped backwards and opposite to the objects it is reflecting.

Materials Protractor Two identical, small plane mirrors Modeling clay Small object (coin, small figure,

etc.) Strip of paper Pen Plastic packing tape

Procedure1. Tape your mirrors together so that they can be opened and closed like a hinge.

You want to leave a slight gap between the two edges (around 1/16th of an inch) to do this.

2. Mark angles of 30, 36, 45, 60, 90, 120 and 180 degrees on a piece of paper using your protractor.

3. Place the hinge of your mirrors at the vertex of your marked angles.4. The first angle you will test will be 180 degrees.5. Place your object (you can embed it in modeling clay if it won’t stand up on

its own) in the middle of the mirrors and look at the reflection. How many objects do you see, including both reflected and real?

6. Keeping the object equally between the two mirrors, move the mirrors together into the other angles you marked out with your protractor. How many

objects do you see at each angle? Is there something about the angle can help you predict how many objects you will see? Is every reflected image the same brightness?

7. Write a word on a piece of paper, and place it in between the mirrors at 60 degrees. Look closely at the second reflection (the reflection of the reflection). Can you read the text? Why do you think this is happening?

Results

You will see an ever-increasing number of objects as you move the mirrors closer together (reducing the angle between them). Whenever you can see a whole number of images reflected, the angle of the mirrors will perfectly divide into 360 degrees. When you look at the reflection of a reflection you will be able to read the text in the mirror, as if you pointed a camera at the object. The reflections should get dimmer (more silvery) as the number of times they are reflected increases

Why?

The mirrors reflect the reflections of other mirrors within 180 degrees of the mirror’s face. When mirrors reflect, the reflected image will be backwards, but if you reflect something twice, it will look normal.

Because light is traveling in a straight line to and from each mirror, the light will bounce a number of times back and forth between the mirrors before it travels from the object to your eye. The number of times the light bounces (and the number of objects that you see) will correlate to the number of times the angle divides into 360. As the mirrors get closer and closer to having zero angle between them, more and more images appear. At an angle of 0 degrees, or when the two mirrors are facing each other, there are an infinite number of reflections.

So, how are you going to accomplish your trick? You can make the text appear by lining up your mirrors and your projector so that the light bounces an even number of times before it gets to your eyes. Using multiple mirrors will also dim the image before it hits the glass plate for the trick.

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