123: Centrifugal Force
Title text: You spin me right round baby, right round, in a manner depriving me of an inertial reference frame. Baby.
Black Hat has strapped James Bond to a centrifuge and claims the centrifugal force will be lethal. Bond objects that there is no such thing, but just centripetal force. This is a common misconception among science teachers which is addressed in the explanation below:
- Observers' point of view (Black Hat, us, etc.)
- James Bond is moving in a circle, and is therefore accelerating. The force keeping him there is an inward force of contact against the centrifuge, a centripetal force. Via Newton's third law, since the centrifuge is pushing Bond inward, Bond is pushing the centrifuge outward. The centrifuge's material is strong enough not to break under this force, however.
- James Bond's point of view
- In James Bond's frame of reference, Bond is at rest. He is kept there by two forces: the above-mentioned inward force of contact against the centrifuge, and an outward centrifugal force. He feels both forces.
As mentioned in the explanation, as the centrifuge rotates faster, the forces needed to keep him in motion get larger, so the force he feels gets larger. This will eventually kill him.
- [James Bond is strapped to a giant wheel suspended from the ceiling. Black hat is standing next to two levers.]
- Black hat: How do you like my centrifuge, mister Bond? When I throw this lever, you will feel centrifugal force crush every bone in your body.
- [Same scene, but a closer shot.]
- Bond: You mean centripetal force. There's no such thing as centrifugal force.
- Black hat: A laughable claim, mister Bond, perpetuated by overzealous teachers of science. Simply construct Newton's laws in a rotating system and you will see a centrifugal force term appear as plain as day.
- [Closer shot, only Bond's head is visible.]
- Bond: Come now, do you really expect me to do coordinate substitution in my head while strapped to a centrifuge?
- Black hat: No, mister Bond. I expect you to die.