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Equilibrium of forces acting at a point

  1. Aug 29, 2008 #1
    1. can an object be moving and still be in equilibrium?
    2. consider a ring with a pin in the center that's not connected to the ring. three weights are attached to the ring at different angles and are hanging from the side of the apparatus where the ring lies. what criteria will decide when the forces on the ring are in equilibrium?
    3. draw a set of three vectors whose sum is zero
    4. how will you estimate the uncertainty of each force acting on the ring?
    5. how will you estimate the uncertainty of each angle measurement?
    6. how much error will be introduced if the table is not level? how could you test this empirically?
    7. what are the units of sine and cosine? does your answer depend on the units of the angle (degrees or radians)?
  2. jcsd
  3. Aug 29, 2008 #2


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    1. Yes, provided by "equilibrium", you mean no net force acting on it. Newton's 1st law covers this.

    2. It's hard to visualise what you are describing here. But if a system is in equilibrium it either moves with a constant velocity or not at all. Rotational equilibrium means that there isn't any net torque about any chosen point.

    3. That's pretty simple. Think of a closed shape consisting of three lines.

    4. Uncertainty is related to measurement, so unless you tell us what instruments are used to measure the force and how you measure them, your question makes no sense.

    5. Again it depends on the level of accuracy of your measuring instrument.

    6. Don't know what you mean here. The apparatus is set up on the table, but what has this got to do with measurement errors? If the tilted table affects the results it would be a systematic error and not a random error. When someone asks "How much error/uncertainty is given in the results", they are usually referring to random errors, not systematic ones.

    7. Certain trigo formulas work in radians but not degrees, but apart from that there is no difference between the two. The units of degrees are well, degrees and you should be able to determine the units of radian measurement by dimensional analysis.
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