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From this 1999 NHTSA report:

5.3.2 Loose Gravel

On loose gravel, each of the nine vehicles stopped in the shortest distance with a panic brake application and disabled ABS [anti-lock braking system], regardless of the loading condition. Stops made on the gravel were lengthened considerably when ABS was active: 24.6% when the test vehicles were fully laden and 30.0% when lightly laden.

The ABS-induced stopping distance increase may be best explained by examining the tire-to-roadway surface interaction during the braking maneuver. It is generally accepted that the plowing of a vehicle's tires into a deformable surface such as loose gravel generates greater stopping forces than if the wheels were allowed to continue to roll over the surface (as in an ABS-assisted stop). Stopping distances made over the gravel surface therefore represent an inherent ABS design compromise. To preserve the driver's ability to maintain directional control of the vehicle while braking, the wheels must not be allowed to lock. By preserving this control, however, stopping distances made over the gravel test surface were extended.

We usually think ABS is about shorter stopping distances, but really it's about two things:

1. Shorter stopping distance, and
2. Preserving steering control while braking

Most of the time these two things do not conflict. In most driving conditions like dry or wet pavement, you get both shorter stopping distance and control.

But on gravel, in order to preserve the driver's control, the ABS results in longer straight-line stopping distance.

Hmm, I wonder if future (post-1999) ABS systems have been updated to let the brakes lock-up on gravel when the vehicle is going in a straight-line, but then revert to anti-lock if the driver is kidding or is attempting to steer. That would be the best of both worlds. The next question would become: How does the ABS "know" the car is on gravel?

New Scientist: Earth rocks could have taken life to Titan (March 17, 2006)

When large enough asteroids/comets hit earth, debris from the impact can be launched into the outer solar system. This would include rocks that originated on Earth? What if those rocks carried primitive life? Simulations show that some of these rocks likely would have made it to Titan, and crashed on Titan at speeds slow enough for simple life to have survived.

MRI machines use very powerful magnets to create those cool 3D medical images. Just how powerful?

SimplePhysics.com has a cool photo gallery of large items (chairs, oxygen tanks, floor cleaners) sucked into an MRI. Click each photo for a pop-up that includes a description.

HowStuffWorks.com gives this example to show the power of MRIs:

The magnetic force exerted on an object increases exponentially as it nears the magnet. Imagine standing 15 feet away from the magnet with a large pipe wrench in your hand. You might feel a slight pull. Take a couple of steps closer and that pull is much stronger. When you get to within 3 feet of the magnet, the wrench likely is pulled from your grasp. The more mass an object has, the more dangerous it can be — the force with which it is attracted to the magnet is much stronger. Mop buckets, vacuum cleaners, IV poles, oxygen tanks, patient stretchers, heart monitors and countless other objects have all been pulled into the magnetic fields of MRI machines. Smaller objects can usually be pulled free of the magnet by hand. Large ones may have to be pulled away with a winch, or the magnetic field may even have to be shut down.