Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Angular velocity questions.

  1. Feb 28, 2008 #1
    1. For an object in circular motion, which of the following is/are directed perpendicular to the plane of the circle?

    Angular Acceleration, Tengintial Velocity, Angular Velocity, Tangential Acceleration, or Angular Displacement?

    2. You are on Earth. Assume that one month is about 30 days and that the moon is about 60 times as far from the center of the circular Earth as you are. Then the tanginitial speed of the moon in its orbit (assumed circular) around the Earth is about

    Equal to your tengential speed, 60 times your tangintial speed, twice your tangential speed, or half your tangintial speed?

    2. Relevant equations


    3. The attempt at a solution

    They're not really matamaticas problems, but test of concept; which I don't really seem to have a grasp of.

    Beyond those, there a few matmatical stumpers.

    Assume that the equitorial radius of the Earth is 6.4x10^6 m and that the length of a day at the equator is 24 hours. You are standing on the equator of the rotating Earth.

    1. What is the period of your uniform circular motion in seconds?

    I calculated 1/86400 cycles per second.

    2. What is the frequency of your circular motion in Hertz?

    3. What is the magnitude of your angular acceleration in rad/s^2

    4. What is your tangential speed in m/s

    5. The plane of your circular motion is certainly the equitorial plane. If an observer in a spaceship high above the pole correctly states that your angular velocity vector is directed toward her, then the spaceship is above which pole? Explain.

    I could calculate the acceleration and speed if I was given a slight hint, but the frequency and "poles" question leave me baffaled.

    Ok, I calculated the tingential speed to be 465 m/s, and the angular acceleration to be 0. Still need help on the proof of concept, the frequency, and poles questions though.
    Last edited: Feb 28, 2008
  2. jcsd
  3. Feb 28, 2008 #2
    Whenever you have a vector described using a direction of rotation, it always points perpendicular to the plane in which the rotation is taking place. Also, it would be good to note that angular displacement is not a vector quantity.
  4. Mar 1, 2008 #3

    Shooting Star

    User Avatar
    Homework Helper

    Frequency is the number of times something happens per unit time. If the period of rotation is T, what would be the frequency? Think for a while.

    The angular velocity is considered positive toward the z-axis when something rotates on the xy plane counter clockwise when seen from the direction of the z-axis.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook