Faster Than a Speeding Bullet

You're looking at an SR-71 Blackbird, the fastest jet-powered plane on the planet. At least, it was the fastest jet-powered plane on the planet. This past weekend, NASA's tiny, unmanned X-43A may have shot the Blackbird down.

On Saturday, NASA took its new plane, which looks something like a surfboard, out to catch some waves--sound waves. An old B-52 bomber tucked it under a wing, carried it 40,000 feet (12,000 meters) up, and let go. A Pegasus rocket strapped to the X-43A's rear-end ignited, carried the 12-foot craft twice as high again, and let go, too.

For 10 fleeting seconds, the X-43A flew alone, under its own jet power, at Mach 7--about 4,800 miles per hour (7,700 kilometers per hour). That's more than twice as fast as a Blackbird, which starts to lose feathers at Mach 3.2--about 2,200 miles per hour (3,500 kilometers per hour). Heck, it's faster than a speeding bullet.

Of course, some might say that getting a rocket boost is cheating--something like throwing a track star off a speeding bus and then saying he ran 65 miles an hour (in the instant before both legs broke). You make the call.

How Fast Is a Speeding Bullet?

Much faster than you think--literally. But
not nearly as fast as you and Superman fly through space.

A bullet fired from a .38 Special might travel 600 feet per second. That's "only" 400 miles per hour (640 kph), slower than the cruising speed of a 747. Yet a high-powered rifle using a specially made cartridge can send a slug speeding away at 4,000 feet per second. That's 2,700 miles per hour (4,350 kph). A typical deer rifle fires a bullet with about two-thirds that speed--still more than twice the speed of sound.

Forget about dodging even the pokiest of these slugs. The electrical signals that move between your brain and your muscles don't go faster than 270 miles per hour (435 kph). The signals involved in thinking and reading move even slower than that. Mercifully, pain signals travel slower still.

But that's not to say that you're some kind of slug yourself. You actually move incredibly fast all the time. At mid-latitudes, the Earth spins at about 700 to 900 miles per hour (1,100 to 1,500 kph), and you, of course, spin with it. Similarly, the Earth goes round the sun at about 65,000 miles per hour (105,000 kph), and you go around with it.

Dizzy yet? You're whirling about even faster. The sun and all its satellites, including you, move around the center of the Milky Way at about 500,000 miles per hour (800,000 kph). And the Milky Way is moving at 1.4 million miles per hour
(2.2 million kph) toward some mysterious "Great Attractor." There are other motions, too, but you get the idea.

Fortunately, we are all saved from perpetual motion sickness by the fact that this tremendous speed is relative. Fire a deer rifle from an SR-71 Blackbird at full throttle, and the bullet will move away from you at a little more than twice the speed of sound. But relative to the ground, it will move at an incredible Mach 5--its speed, plus the speed of your Blackbird. It's all about your frame of reference.

U.S. Air Force Captain Joseph Kittinger learned this firsthand. In 1960, as part of a military test, he parachuted from a balloon gondola more than 100,000 feet (30,000 meters) above the Earth. While in freefall, his body reached a speed of 614 miles per hour (988 kph)--nearly breaking the sound barrier. And yet, lacking any reference so far above the ground, he said, "I have absolutely no sensation of the increasing speed with which I fall."