Astronomy 101 - How to use angular measurement in determining the size of planets?
Q. I don't quite understand how, if we know the size of an angle, that we are able to calculate an estimated size of a planet. The only thing that's clear about this subject for me is apparent size (distance larger, apparent size smaller but actual size larger). Will someone please help me by explaining angular measurement in plain English?
Asked by inca_girl - Tue Sep 15 14:18:21 2009 - - 3 Answers - 0 Comments

A. For objects that cover a relatively small area of sky (as all distant planets do!) the following formula relates their actual size, apparent size, and distance: D = X * d / 206,265 In this formula, D is the actual size of the object, d is the distance to the object, and X is the angular size of the object in arcseconds. Again, this only works for things that will subtend a relatively small angle, like distant planets. For larger, closer objects the calculation doesn't work as well. I hope that helps. Good luck!
Answered by Lucas C - Tue Sep 15 14:59:38 2009

Find the magnitude of the angular acceleration of the wheel ?
Q. A wheel starts from rest and rotates with constant angular acceleration to reach an angular speed of 12 radian/seconds in 3 seconds. (b) the angle in radians through which it rotates in this time?
Asked by NYJETS - Tue Apr 15 13:12:26 2008 - - 1 Answers - 0 Comments

A. At time=0 angular speed=0. At time=1 angular speed=12/3=4. Angular acceleration 4 per sec. Surely. (b) Should have thought you could use 's=ut + (1/2)at^2'. So required angle = (1/2).4.9.
Answered by Lugo T - Tue Apr 15 13:25:55 2008

How do I design a simple device that demonstrates the energy, momentum, and angular momentum principles?
Q. My physics teacher has asked me to design a physical device within a week that will demonstrate to him my general understanding of the conservation of energy principle, the momentum principle, and the angular momentum principle. Any ideas on how to construct this device or a Goldberg device that will be easy to put together?
Asked by Albert C - Thu Jul 2 00:46:58 2009 - - 1 Answers - 0 Comments

A. Flywheel driven electric car. (A model car using a flywheel + motor/generator instead of a battery) You "charge up" the car by using an external source of electricity to drive the motor to speed up the flywheel. Then when running, the flywheel turns the motor which generates electricity to drive the motors connected to the heels. Or, simpler, but messier, a boat driven by a propellor. The movement of the water backward drives the boat forward - linear momentum; the turning of the propellor also causes tilt of the boat (which is why many ships have two counter-rotating propellors); and there is the efficiency of different sizes of propellors - energy vs. momentum. (You can do the same with a helicopter, but helicopters are much harder to… [cont.]
Answered by simplicitus - Sat Jul 4 16:46:12 2009