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.