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Homework Help: Earth rotation is slowing down

  1. Nov 14, 2008 #1
    http://images42.fotki.com/v1375/photos/1/1424948/6925600/EPSON008-vi.jpg [Broken]1.[/URL] The problem statement, all variables and given/known data
    A man reading a newspaper stating "Earth's rotation is slowing down". there's a fishing bowl next to him. The water in the fishing bowl is leaned towards the right side. What direction is the man facing if the newpaper article is true??
    Also explain why.

    2. Relevant equations

    choices are North,South, EAst and West.

    3. The attempt at a solution

    i Thought it would be west. but i truly dont know why.
    I tried uploading the pic on here, but i dont know how =x
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Nov 14, 2008 #2


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    Actually, I would be concerned about thinking anything without knowing why!

    If you were in a car driving east that was slowing down, which way would YOU "lean"?
  4. Nov 14, 2008 #3
    centripetal force, that is the clue. When you are travelling clockwise in a circle, you REQUIRE mv^2/r amount of force towards the centre to remain in circular motion, so you will tend to lean "outwards".
  5. Nov 14, 2008 #4
    thank you for both of yall help!!!!
    I finally got the picture up!
    So, according to the picture, the man is facing west because if the earth is slowing down, centripetal force is a little off and therefore causes the fishing bowl's water to lean.
    am i correct??? thank you for all responses...I appreciate every help!!
  6. Nov 14, 2008 #5
    So the man is facing west due to centripetal force right???
  7. Nov 14, 2008 #6


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    I don't believe the centripetal acceleration is what they are asking about here; they are asking about the transverse acceleration.

    Did you answer the question in the post from HallsofIvy? That's the important physical idea (and does not deal with centripetal acceleration at all).

    Then answer this question: which way is everything being carried due to the earth's rotation: north, south, east or west?

    If the earth is slowing down, which way will the water be leaning?

    Finally, once you know which way the water is leaning in the picture, which direction is the man facing?
  8. Nov 14, 2008 #7


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    Looks to me like he is facing at right angle to the direction the Earth has put the brakes on.
  9. Nov 14, 2008 #8
    to asnwer hallsofIvy question...if i was driving east and slowing down i would lean WEST right???
    answer to alphysicist..I don't know which way is everything being carried due to the earth's rotation?? I think that's my whole problem??
    "I'm feeling a lil ashame that i dont know this = x"
    thank you for all the help..greatly appreciates it
  10. Nov 14, 2008 #9


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    No; if the car is heading east and you slam on the brakes, which way does your body "lean"?

    You feel like you are "being thrown" toward the front of the car, right? Which means your body leans to the east; in other words, if you're being carried to the east and you are slowing down, your body leans to the east.

    Think about a globe, and picure it spinning the same direction as the earth really rotates. If you pick a city on the globe, is its motion to the north, south, east or west?
  11. Nov 14, 2008 #10
    i searched the internet and it says everything is carried to the east, so if the earth is slowing down, the water would be leaning south.
    So if the bowl is leaning south, then the man is facing West?? am i right???
    one more question, what is transverse acceleration... I'm sorry for so many questions...i just want to make sure I'm clear about the answer and to make sure i understand this problem...Many many thanks!!!
  12. Nov 14, 2008 #11


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    No, it's just like the car I mentioned in my last post. If you're moving east, and slowing, you lean to the east.

    So which was is the man facing?
  13. Nov 14, 2008 #12
    yea i just read your last post, i was typing my previous post and didnt get to read your last post.... so actually the water is leaning to the east and the man is facing south.
    I'm sorry for asking so many questions and pardon my lack of knowledge, but what is transverse acceleration because I guess that's the explanation to "why" for the problem..
  14. Nov 14, 2008 #13


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    It has a technical definition but I don't know if that would help much (its equal to [tex]\dot{\bf \omega}\times{\bf r}[/tex], where the dot is a derivative and r is in the rotating system).

    To give a more intuitive approach, I would probably talk about something along the lines of the problem that you were solving here. The idea is that if an object is in a rotating system (like the earth) and the angular velocity of the system is changing (like the earth slowing down), then there is a transverse acceleration acting on the object (because it has to slow down too).

    You can also think about sitting on a merry-go-round, facing the center. If you are sitting on one spot, and the merry-go-round is rotating at constant speed, there is just centripetal acceleration. The important thing is you feel like you are being pushed backwards (away from the center) because of your acceleration towards the center.

    Now if the merry-go-round slows down (lets say it slows down very rapidly), you have to slow down, too. And the only way this happens is if there is a corresponding acceleration on you to the side. And that acceleration is the transverse acceleration. (If the merry-go-round is stopped too quickly you might fall over to one side--you'll fall on the side opposite the acceleration.)

    (Also, when you studied circular motion, the transverse acceleration was probably called the tangential acceleration, and equalled (r * alpha). It only appeared when the speed of the object moving around the circle changed.)

    Sorry this is so wordy, but I think you will need to think about how these things work together, especially in the problem in your post until it makes sense.
  15. Nov 14, 2008 #14
    thank you so much for your answer....when i first saw the post ...i was like wow...so long...ehhehe but it does give me a clearer picture of the situation..thank you so much!!!
  16. Nov 14, 2008 #15


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    Glad to help!
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