WonderQuest:  On the web since 1997...      

Sky diving from the edge of space, Boiling ostrich eggs

Q: Doesn't terminal velocity of a skydiver also depend on his altitude? This isn't mentioned in your terminal velocity question. I remember seeing on the discovery channel about a skydiver who jumped from the edge of the earth's atmosphere (in a space suit) and broke the speed of sound.

[US Air Force] US Air Force Captain Joseph Kittinger drops from the edge of space

Q: As he fell closer to earth, I'm guessing that his terminal velocity decreased. Is this correct? -- Steve Schultz, Waterloo, Ontario, Canada

A: Yes, the terminal velocity of a skydiver does depend on his altitude because it's the resistance of the air that brakes the fall.

As the falling body plows through the air, it hits air molecules and the molecules exert an opposite force. The resistive force depends primarily on two things: the falling-object size and speed. The bigger the size, the more air molecules it must force its way through. The bigger the speed, the more molecules the body strikes per second and the greater the force of molecular impact.

When the air-resistance force equals the downward force due to Earth's gravity then the falling speed becomes a constant--the terminal velocity. The higher you go, the thinner the air and the less it resists falling bodies.

You probably referred to the stupendous feat of US Air Force Captain Joseph Kittinger. Although he did not break the speed of sound, he came close-- nine- tenths the speed of sound at his altitude--a colossal 614 mph (990 km/hr). He dove 4.5 times faster than most skydivers who start at much lower altitudes where the air is thicker. He could do this by falling through almost no air: 1.5 % of the density at sea level.

On 16 August 1960, Kittinger set the world's record (which remains unbroken) for the longest (19.5 miles) and fastest (4 minutes and 36 seconds) skydive. He reported his experience in the National Geographic--starting in the helium balloon that he floated to an altitude of 102,800 feet (31,330 m). This high, the sky is black and the Sun intense.

"Sitting in my gondola, which gently twisted with the balloon's slow turnings, I had begun to sweat lightly, though the temperature read 36 degrees below zero Fahrenheit. Sunlight burned on me..."

Nineteen miles high, he stepped out and began to fall. " No wind whistles or billows my clothing. I have absolutely no sensation of the increasing speed with which I fall. [The clouds] rushed up so chillingly that I had to remind myself they were vapor and not solid."

He fell a mile, opened his parachute, and fell another mile with the opened chute before he felt the slightest slowing. Yes, his terminal velocity continued to change on the way down as the air density increased.

Good point.

Further Surfing:

WonderQuest: We can fall only so fast

WonderQuest: Falling raindrops hit 5 to 20 mph speeds

The Physics Factbook: Speed of a skydiver

Q: How long does it take to boil an ostrich egg? I am not thinking of cooking or eating one, but I was asked this question in a trivia game. The answer was not revealed. I searched the Internet and got conflicting answers: 40 minutes, 2 hours, and 4 hours. --"Megaptera", Las Vegas, Nevada

[Corel] An ostrich lays a big egg--the biggest.

A: The answer is... 48 to 60 minutes for a soft-boiled egg and 1 to 1.5 hours for a hard-boiled one--at sea level. You might wonder what hat I pulled these numbers from. It wasn't an easy hat to find. As you discovered--the numbers vary all over the map. So I contacted ostrich ranchers all over the map: England, Africa, Canada, Australia, Malaysia, and the USA. That's the answer I got.

After hard boiling the egg for 1.5 hours, the Flemings of Saanichton Christmas Tree & Ostrich farm in Canada, make deviled ostrich egg sandwiches. One ostrich egg, scrambled, fills a 12-inch frying pan to the brim. Ostrich eggs taste similar to chicken eggs: light and fluffy. (Related: recipe for deviled ostrich egg sandwiches.)

The boiling times vary, I suspect, for a couple of reasons. Low answers (like 40 minutes for a hard-boiled egg) result from blithely scaling up the time it takes to boil a chicken egg. That won't work because an ostrich egg has a shiny, whitish shell built to sustain a 345-pound weight--an adult male ostrich. That's a whopping thick shell the heat must penetrate before it even starts cooking the egg. The shell stays too hot to touch for two hours afterwards. Beware.

Perhaps a fear of undercooking a six-inch long, grapefruit-size egg gives rise to the extremely long time estimates. Who wants to crack a "hard-boiled" ostrich egg and get egg on their face?

By the way, the ostrich egg is the largest egg laid by all living creatures but the smallest bird egg in relation to the hen's size.

Further Surfing:

Ostrich Wonderland: History of ostriches

Australian Ostrich Association: Ostrich information

Saanichton Christmas Tree & Ostrich farm: ostrich egg shells

Ostcorp: Ostrich facts

Cilabi Ostrich Ranch: Ostrich facts and tales

(Answered Jan. 10, 2003)