Be cool

Pretty soon it’ll be time to fire up the air conditioner for this year. We’re going to find out how the cool got into air conditioning. Today, on Engineering Works!

If you were paying attention to the news a while ago, you probably know this already. This year, 2004, is the 102nd anniversary of the invention of air conditioning.

Mechanical engineer Willis Carrier invented air conditioning as we know it in 1902. His first customer was a commercial printer in New York City who needed help dealing with what the heat and sticky humidity of July were doing to the paper in his print shop.

Before Carrier designed that first air conditioning system, all we could do about heat and humidity was to move the air around — with fans. Big ones; little ones; the cardboard ones your grandparents fluttered to keep cool in church.

Fanning the air past your face made you feel less uncomfortable. But Carrier’s air conditioning was different. He didn’t just move the air. He cooled it.

Air conditioning cools because when a gas under pressure expands, it absorbs heat. That’s physics. Blow warm air across some pipes with an expanding gas in it and the air gets cold. That’s engineering. Blow that cold air into a room and you get comfortable.

Simple. But it took Willis Carrier’s engineering ingenuity to turn physics into the air conditioners that keep our homes and cars and the places we work cool and comfortable in hot weather.

How does the cookie crumble?

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One of humanity’s cosmic questions has finally been answered. And by an engineer, no less. We’ll check it out today on Engineering Works!

You’ve heard people talk about it all your life, so it must be important. Oh, well, they say, that’s the way the cookie crumbles. But no one ever talks about how that happens. How does the cookie crumble? No one ever said, because no one knew.

Until now. Wherever you are, sit down. Mechanical engineering researchers in Great Britain have figured out what makes the cookie crumble.

They used a special laser measuring technique called digital speckle pattern interferometry to look closely at cookie dough as it gets baked into cookies. What they found is more complicated than you think. Cookies hot from the oven pick up moisture from the air around the edges as they cool. But they’re also drying out in the middle. Some crack from the stress.

We can hear you snickering from here. So what, you say. Who cares, now that we know how the cookie crumbles? Actually, the baking industry cares — quite a lot.
Like other businesses, satisfied customers are important to the folks who bake cookies. You don’t like to open a package of cookies and pull out a crumbled one to have with your mid-morning coffee. Knowing how to fine-tune the way cookies are baked could make a big difference.

So, pour some fresh coffee and pass the cookies — non-crumbled, of course.

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Engineering is music to your ears

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Just about anything can make a sound. It takes skill – and engineering – to turn sound into music. Find out how engineers do that, today on Engineering Works!

You’ve probably blown across the top of an empty bottle. The bottle vibrates, creating sound waves. Add water to the bottle and blow again. Hear the difference? You’ve changed the bottle’s pitch – how high or low it sounds.

Things like valves, pistons and springs change pitch in many musical instruments. That’s right: those parts you find in engines and machines also help musicians play mellow tones and reach high notes.

You’re catching jazz legend Miles Davis on trumpet right now. Trumpets and horns were simply long tubes until around 1815. Two musicians in Germany developed a spring-controlled sliding valve that increased the range of notes those instruments could play. They based the idea on valves used to control air, water and steam in blast furnaces and steam engines, the high tech of their time.

This really big machine – the pipe organ – got its start thanks to an engineer in Egypt more than two-thousand years ago. We even know his name: Ktesibios of Alexandria, inventor of the water clock. He used water pressure to pump air to lots of pipes at the same time. Most organs built today use electric air pumps to power their pipes.

Oh-oh, is that a Martian behind you? Fans of old science fiction movies probably recognize these eerie sounds, although you may not know the instrument that makes them. The theremin – named for its inventor, physicist Leon Theremin, in 1919 – doesn’t have any keys or valves at all. Instead, you play it by moving your hands to control radio frequency sound waves.

Got that? Okay. Let’s take it from the top!

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Knee bone connected to the … artificial bone

Engineers build bridges and buildings all the time. How about engineered bones? We’ll look into it today on Engineering Works!

Sometimes bones are more trouble than they’re worth. Especially when joints like knees or hips go bad. We’ve got metal and ceramic replacement joints, but they don’t last as long as we’d like them to — 10 years and you’re replacing the replacement. That’s no fun.

Most joint replacements fail because the glue that doctors use to anchor them in place wears out. That usually happens because the ceramic bone in replacement joints isn’t quite the same as real bone. It’s got the same ingredients, but it’s not the same. Real bone is solid and hard on the outside and porous on the inside – think a sponge inside a pipe. Artificial bone is solid and hard all the way through — no pores inside. And that’s the problem.

Medical researchers say that if artificial bone had pores like real bone, the real bone would grow into the artificial bone over time. It wouldn’t matter if the glue holding an artificial joint in place wore out.

Engineers are busy trying to figure out ways to make artificial bone more like real bone. They’re working with NASA to do experiments in space they think will give them clues to how to make artificial bones with the same solid and porous structure as real bones.

You’ve probably had enough bones for today. So have we.