frank@scorplx.UUCP (Frank Pavelski) (08/28/84)
*****
*****
Since I have only had a year of high school kinematics, my question may
seem childish to all you experts. Anyway here it is:
When you are traveling at high speed in a circular path in your car,
anything attached to the rear view mirror (i.e. fuzzy dice) tends to
move outwardly to the path motion.
Now, if I remember correctly, in circular motion, the force vector is
directed radially inward as is the acceleration vector.
This seems contradictory. Is this an example of the rule "objects traveling
forward tend to remain so"? One person I asked claimed that it was because
the car tilted when banking a turn. I find this one a little difficult to
believe.
Any comments would be appreciated.
Frank
(a.k.a. a gulf coast beach bum)Gilman.ES@XEROX.ARPA@sri-unix.UUCP (08/30/84)
Simply put, when the car is travelling straight, the dice are hanging straight because there are no other forces on the dice than gravity. Now, because an article in motion tends to stay in motion, when you turn the car, the dice still tend to go forward, but the rear view mirror is turning to the left. When you consider the dice and the forces on the dice, there is the force of the string composed of two components: the old force to counter gravity, and a new force caused by the car's turning. Now when the car turns at a constant rate, and goes in a circle, the dice are always tending to go straight, but the car is always turning. The force due to the car's turning is called centripetal force, since it is directed toward the center of the circle around which the car is going. By measuring the angle that the string makes to the vertical, you can determine what the component of the force of the string is in the direction of the center of the circle, and you have a crude centripetal accelerometer.
gwyn@Brl-Vld.ARPA (08/31/84)
From: Doug Gwyn (VLD/VMB) <gwyn@Brl-Vld.ARPA> The force is what you would have to apply to get the object to move in a circle. Since the vertical string does not transmit the force being applied to the vehicle to the dice, they prefer to keep moving in their original straight path. However, soon the string IS able to transmit a force and the situation reaches equilibrium with the dice somewhat higher above ground than they started off.
bane@umcp-cs.UUCP (John R. Bane) (09/06/84)
If you have a helium balloon in the car with you (and your fuzzy
dice), you will see something really strange: the balloon will lean in the
opposite direction the dice do. The explanation I've always heard for this
is that the balloon's motion is dominated by buoyant forces; when the air
in the car feels a centrifugal force and goes one way, the balloon goes
the other way.
--
ARPAnet: bane@maryland
CSnet: bane.umcp-cs
Uucp:...{allegra,seismo}!umcp-cs!bane