Archive for Tuesday, May 20, 2008

Weird science

Great science projects don’t always have to come from a laboratory

You don't need to build a campfire to get your fill of gooey marshmallow-and-chocolate s'mores this season. Just tap into the sun, the fuel source that people around the world use to power solar ovens.

You don't need to build a campfire to get your fill of gooey marshmallow-and-chocolate s'mores this season. Just tap into the sun, the fuel source that people around the world use to power solar ovens.

May 20, 2008

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Bubble Mania: Dip a plastic drinking straw into the liquid. Insert the end of the straw into the bubble and gently blow. The interior bubbles will pass through the skin at the bottom of the large bubble and cling to the outside.

Bubble Mania: Dip a plastic drinking straw into the liquid. Insert the end of the straw into the bubble and gently blow. The interior bubbles will pass through the skin at the bottom of the large bubble and cling to the outside.

If you think science happens only in a laboratory, you've got to get out more. The great outdoors is filled with opportunities to learn about the laws of physics, chemistry, aerodynamics and more.

And you don't need expensive or fancy equipment to take advantage of them. Just check out the amazing experiments that follow. All it takes to pull them off is a few household supplies, some scientific curiosity and a little piece of the world outside your front door.

PROJECT 1: Bubble Mania

Time and again, science has shown us that first impressions can't be trusted. Consider the bubble: At first glance, it looks like the most fragile thing in the world. Yet under the right circumstances, it can be surprisingly difficult, if not impossible, to burst - as the two tricks here illustrate.

You Will Need:

8 1/2 by 11-inch sheet of card stock

Tape

Scissors

Bowl and spoon

1 cup plus 2 tablespoons water

2 tablespoons dishwashing liquid

2 tablespoons glycerin (sold at craft and drug stores)

Plastic drinking straw

1. Make a bubble blower by rolling the card stock into a cone and securing it with tape, as shown. Evenly trim the narrow end so it measures 1/2-inch in diameter. Trim the wide opening to even it too.

2. In the bowl, gently stir together the water, dishwashing liquid, and glycerin, and you're ready to perform the following tricks.

Trick 1: The Unpoppable Bubble

What to Do

1. Dip the wide end of the cone into the bubble solution and hold it there for a few seconds to absorb the mixture. Tap off the excess liquid and then quickly dip the cone again. With the cone pointed toward the ground, gently blow a large bubble. Leave it attached to the end of the cone, using your finger to cover the cone's tip.

2. Now stick the point of the scissors into the bubble. It should pop instantly. Try it again, but this time, first dip the scissor points into the bubble solution. They should pass right through the bubble's "delicate" skin without breaking it.

What's Happening

Trick 1: There are two main ways a bubble pops. The first is when its watery wall evaporates (adding some glycerin to the bubble solution slows down this process). The second is when something dry tears a hole in the wall, as when you poke it with the bare points of a pair of scissors. Dipping the blades into the bubble solution beforehand, however, gives them liquid edges, and the bubble wall simply flows around them.

Trick 2: Inside-Out Bubbles

What to Do

1. Blow a large bubble as you did in the first trick.

2. Dip the plastic drinking straw into the liquid (be sure to wet at least 2 inches of it). Insert the end of the straw into the bubble and gently blow to create one or more smaller bubbles inside it. Then watch. The interior bubbles will pass through the skin at the bottom of the large bubble and cling to the outside.

What's Happening

Trick 2: As with the scissors, coating the straw with solution allows you to insert it in the big bubble and blow smaller bubbles inside. But why don't those small bubbles stay in there? Because their proportion of air to liquid is smaller than the bigger bubble's, they are denser. Consequently, they sink and fall through the bottom of the bigger bubble. Still, they don't weigh quite enough to break free completely, so they simply hang in place.

PROJECT 2: Solar S'mores

You don't need to build a campfire for your kids to get their fill of gooey marshmallow-and-chocolate s'mores this season. Just tap into the sun, the fuel source that people around the world use to power solar ovens. Here's an easy pizza box model that will let you catch enough backyard rays to cook the coolest s'mores on the block.

You Will Need:

Large pizza box

Pencil and ruler

Craft knife

Aluminum foil

Scissors

Glue stick

Black construction paper

Clear packing tape

Clear plastic (we used 2 sheet protectors, available at office supply stores)

Graham crackers, chocolate bars and marshmallows

Stick or dowel

What to Do

1. On the top of the pizza box, draw a square that is an inch smaller than the lid all the way around. Use the craft knife (adults only) to cut through the cardboard along three sides, as shown, and then fold the cardboard up along the uncut line to form a flap.

2. Glue aluminum foil, shiny side out, to the bottom of the flap, keeping it as wrinkle-free as you can.

3. Glue another piece of foil to the inside bottom of the box, then tape black construction paper on top of the foil.

4. Tape clear plastic to the underside of the lid to seal the opening created by the flap. For the best results, the seal should be as airtight as possible.

5. Place your oven outdoors in direct sunlight with the flap opened toward the sun. For each s'more, center two graham crackers on the construction paper. Top one with chocolate and the other with a marshmallow. Close the box and then use a stick or dowel to prop the flap open at the angle that reflects the most sunlight into the box (check it periodically to adjust the angle). Within an hour (or sooner if it's a really hot day), the chocolate squares and marshmallows should melt enough to assemble into s'mores.

What's Happening

If you've learned about the greenhouse effect, you may have already guessed how the oven works. The foil flap gathers sunlight and reflects it through the plastic and into the oven, doubling the amount of incoming light. The black paper absorbs the light and converts it to heat, and the clear plastic allows the sun to shine in while keeping all that heat from escaping. (In the greenhouse effect, atmospheric gases allow sunlight to pass through to the earth's surface but keep the heat it generates from escaping back into space.) As more light hits the black paper, more heat is created and trapped. After an hour or so on a sunny day, the oven can be as hot as 275 degrees - hot enough to melt chocolate and marshmallows.

PROJECT 3: Cardboard Boomerang

It's hard to watch a boomerang soar off through the air and return to the thrower without imagining that some kind of magic is at work. In fact, it's not magic at all - just physics taking flight.

You Will Need:

8-inch square of cardboard cut from a cereal box or poster board

Pencil and ruler

Scissors

Ballpoint pen

Decorative stickers or colored markers

What to Do

1. Depending on whether you are left-handed or right-handed, mark the cardboard square as specified and then cut out the boomerang. It will resemble a chunky X at this stage. Use the scissors to round the ends for safety.

2. With the ballpoint pen, score along the fold lines (shown as dashes in our diagram) and then fold the cardboard down to create 45-degree flaps. If you like, decorate the boomerang with stickers or colored markers.

3. Try out your boomerang on a calm day, standing 20 feet away from people or obstacles (boomerangs are notorious for getting caught in trees or landing on roofs). Hold the boomerang nearly vertical (not horizontal, as you would a flying disk), with the pencil lines visible. Flick your wrist to add spin as you toss it forward and slightly up-ward. It should start to turn and then flatten out as it coasts back to you. The easiest way to catch it is to clap it between both hands. Don't be surprised if it takes you a few tries.

What's Happening

There's a lot of physics going on here, with your boomerang acting like a set of wings and a spinning gyroscope.

For starters, by bending back the edges of the boomer-ang arms, you turn them into curved wings, like those of an airplane. The curves cause air to move more quickly over the wings' tops than the bottoms, creating lift. That's what keeps the boomerang from falling to the ground.

The reason the boomerang comes back to you has to do with its spinning motion, similar to the way a gyroscope or top spins in a circle. If you're interested in the details of how this works, we like the explanation at howstuffworks.com/boomerang.htm.

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