Tuesday, July 31, 2007

How Does a Microwave Oven Work?

Sorry about the delay in posting. There has been much to do in the scientific world of Dr. Dave. Plus the last Harry Potter book came out and, well, I had to read it.

In an earlier post about Pyroceram, I said I would explain how microwaves work. As promised, here it is!

Microwave ovens are a cool invention that makes cooking food really simple and fast. You can use a microwave oven to heat things in a matter minutes compared to the longer cooking times in a normal oven (called a convection oven).

So how does a convection oven work?

Convection ovens work by heating the air inside it using fire or electricity. When heated to the desired temperature, food is placed inside so it can cook.


Have you ever thought about how food cooks in an oven?

Let us imagine we are baking a cake.

After making the batter, it is poured into a pan, which is placed inside a preheated oven. The hot air surrounding the cake batter warms the outside first. Eventually, the insides will get hot. If you do not bake it long enough, the outside may look like it is ready, but the insides could still be batter!

Microwave ovens, unlike a convection oven, do not get hot. Instead, it uses microwaves (strong radio waves), which have the special ability to pass through things like ceramics, glass, and some plastics. More importantly, microwaves have the ability to make water, sugar, and fats inside your food spin and move.

So how does the food get hot?

Try this little experiment. If you rub together really fast, your hands will get warm because of friction.

Now imagine the water, sugar, and fats inside of your food rubbing against each other millions of times every second. Most food gets cooked in a microwave for one or two minutes. That’s 60 to 120 seconds, which means that the water, sugar, and fats in your food is causing a lot of friction, which makes heat that can cook your food.

If you think about it, microwaves ovens cook your food from the inside!

Now that’s cool.

Dr. Dave

Tuesday, July 10, 2007

A Jet Plane Made of Plastic and Fabric!

Boeing unveiled its new 787 Dreamliner on 7/8/07. At first glance, it looks like other airplanes, only sleeker. The Dreamliner is truly different, both inside and out.

The 787 is set apart from other passenger jets because it is built from composite materials. According to the Boeing website, the 787 is half composite, which is much more than any passenger jet ever made!

What are composites?

Composites are materials that are made of two or more things that have different physical properties. Bricks, made of mud and straw, are an example of composites used long ago by the ancient Egyptians.

Why are composites important?

Let us imagine what would happen if we built a home using only straw or only mud.

A home built of straw alone would probably blow away (remember the story of the Three Little Pigs?).

A home built from dried mud would not last very long because the bricks would eventually fall apart.

When both straw and mud are mixed together, they work together. Straw provides a matrix, or a support structure, that mud can hold on to so it does not fall apart. The mud makes the straw stronger by filling in the empty spaces around the straw fibers. Buildings made from composite bricks by the Egyptians were strong and lasted a very long time.

Although modern composites are much more advanced, they work by the same principle: two different materials mixed together to make a much stronger final product.

The composites used in the Dreamliner, called Carbon Fiber Reinforced Plastics (CFRP for short), are among the most advanced composites used today.

What is CFRP?

Carbon fiber is a long thin thread of a carbon polymer that is bundled together in small ropes. Each individual thread is very strong, and when it is bundled, it is even stronger!

I think of carbon fiber as the straw in the brick example above.

The carbon fiber ropes are then weaved together to make a fabric.

Here is what carbon fiber fabric looks like:

The fabric is then coated in a special plastic and molded into the desired shape. Depending on how the threads are weaved and the type of plastic used, CFRP of different strengths can be made.

CFRP is very strong and very lightweight; it has been used to make bike frames, boat hulls, race cars bodies, kayaks, laptop computer cases, musical instruments, plane parts, and skateboards!

Composites like CFRP have been use to manufacture passenger airplane parts for over a decade. Smaller private planes like the Diamond Star (the kind I fly) has a body that is made almost entirely of composites.

Here is a picture of a Diamond Star:

The 787 Dreamliner is the first large passenger jet to have its body made mostly of composites. This will help to keep the airplane’s weight low so it can carry more passengers and fuel, allowing it to fly very far.

Here is a picture of the piece of the 787 composite body.

There is a small company called Scaled Composites that has been using composite materials to makeinteresting planes for a long time. Scaled Composites was responsible for designing and making the Voyager, Global Flyer, and (my favorite) White Knight and Space Ship One.

This a picture of White Knight carrying Space Ship One.

From skateboards to the 787 Dreamliner, composites have found multiple uses in our daily lives. All of this is made possible by science.

Dr. Dave

Sunday, July 8, 2007

How Do Hot Air Balloons Fly?

To explain how hot air balloons fly, ask yourself the following questions:
  1. Is your home is warmer upstairs than it is downstairs?
  2. Have you ever noticed that the hot air from smoke stacks always goes up into the sky?
This occurs because warm air rises and cold air descends.

Now, if that warm air could be captured and kept warm, then we'd have a hot air balloon!

Here's a picture of a hot air balloon:
How is it flown?
Hot air balloon pilots control their altitude changing the temperature of the air inside the balloon.

Use the following illustration as a guide to a hot air balloon:
To gain altitude, pilots use burners to warm the air inside of the envelope (the balloon).

To reduce altitude, pilots open vents at the top of the balloon to slowly release the warm air.

The direction of flight is controlled by the wind.

This YouTube video has a good information on hot air balloons:

You can read more about hot air balloons here.

Pretty cool!

Dr. Dave

Monday, July 2, 2007

From the Space Program to your Kitchen!

You may have a high-tech piece of cookware sitting in your kitchen!

In the 1950s, scientists developed a glass-ceramic material called
Pyroceram©. It probably looks very familiar to you. This material is heat resistant, durable, and invisible to radar!

This stuff was once used by the military and space program. My favorite use? Missile nose cones!

Pyroceram © was later used in kitchens because someone realized that it would make great cookware. It has changed names over the years, but Corning is the company that continues to use this technology – unbeknownst to moms everywhere!

I think the coolest part is that it is invisible to radar. This feature makes it perfectly suited for use in a microwave oven.

Microwaves and radar are related. Because Pyroceram is invisible to radar, this means that it is also invisible to microwaves. 

I think it’s really cool that dinner could be served in something that evades radar like the B-2 stealth bomber!
That's what I call everyday science. Pretty cool!

Dr. Dave

Sunday, July 1, 2007

How Does Sunscreen Work?

The sun is a gigantic atom-smashing machine that makes heat and light. It is the reason why you can enjoy a day at the beach or a dip in the pool, especially on a hot summer day.

The sun also emits harmful UV rays that are responsible for sunburns; too much exposure can cause skin cancer.

What’s Inside?
Sunscreen contains chemicals that reflect or absorb harmful UV rays. When applied to the skin, the thin layer of sunscreen does not allow UV rays to touch your skin.
Sunscreen has to be reapplied every few hours because swimming and sweating washes it off. Did you know that UV rays also damage the chemicals in sunscreen? It’s true! Sunscreen works because the chemicals are being sacrificed to save the skin!

Why do some lifeguards look like they are wearing white paint on their nose?

That white stuff is zinc oxide; another common chemical is titanium dioxide. Both of these chemicals reflect UV rays.

Other kinds of chemicals absorb UV rays. These have funny names like oxybenzone and avobenzone. There’s a long list of chemicals found in different sunscreens.

Did you know that these chemicals are also found in lip balm, lotions, and make-up?

If you feel adventurous, read the ingredient label on the back of a box. I know that there are many funny chemical names, but look for the ones you know!

How do you know the strength of the sunscreen? The standard is called Sun Protection Factor, or SPF.

Sunscreen with a higher SPF rating means that it has more chemicals in it that absorb or reflect UV rays.

Dr. Dave’s Tips
  • Wear sunscreen if you are going to be outside for a long time.
  • Reapply sunscreen after swimming.
  • Wear a hat and sunglasses to protect your eyes!
That’s all for now!

Dr. Dave