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Homework Help: Physics - Inclined Plane - Experimental Investigation

  1. Apr 22, 2013 #1
    1. The problem statement, all variables and given/known data

    A wooden box is at rest on a ramp inclined at an angle Ө to the horizontal. W is the weight of the box and its contents. A frictional force prevents the box sliding down the ramp. A reaction force acts on the box perpendicular to the inclined plane. The inclined plane is hinged at its lower end so that it can be easily lifted to alter the angle Ө.

    Describe how you would investigate the relationship between W and the angle, Өs, at which the box just starts to slide down the ramp.

    Image is attached.

    2. Relevant equations

    I don't feel equations are need, except perhaps possibly the resolved components of W. These being mgsinӨ (the component of weight parallel to the slope), and mgcosӨ (the component of weight perpendicular to the slope). Very unlikely that F = µR will be needed.

    3. The attempt at a solution

    I've been told I need to consider the following:

    • What measurements do I need to take (i.e. what are my x and y variables)?
    • What measuring instruments shall I require to make these measurements?
    • State an appropriate range and interval for my independent axis.
    • Plot a graph of y variable against x variable.
    • Conclude what the results would look like, and what they represent/theorise.

    I think my independent variable is Ө, and I could measure this using a protractor. I could use intervals of 10°, and take a range of 10° to 80°.

    My main problem is not being sure what my dependent variable would be, as without knowing that I can't state what my plotted graph would be or even begin to think what it would look like plotted and theorise.

    Help would be appreciated!


    Attached Files:

    Last edited: Apr 22, 2013
  2. jcsd
  3. Apr 22, 2013 #2

    Simon Bridge

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    Don't worry about that ... start out be describing the experiment.

    "to find the relationship between the weight of the box and the maximum angle that static friction will hold it."

    this is where your equations go - use your physics knowledge to predict the relationship that you are trying to find.

    describe how you are going to do the experiment.

    just a table of your measurements

    Here is where your graph goes ... by convention, the variable under your control goes on the horizontal axis. In physics we just use whatever makes the math easy.

    It is a good idea to change things so that the graph is a line, then you can use the slope of the line as support (or otherwise) for the theory. i.e. your theory relationship may be θ=g√W ... if you plot θ vs W you will get a curve ... but if you plot θ vs √W you will get a line. If the theory is right, then the slope of the line should be close to the value of g in the theory. Much more useful.

    *** Right to this point is what you need to figure out to get full marks.

    This is where you rewrite the "aim" as the answer to a question and tack on what you found out.
  4. Apr 23, 2013 #3
    The independ variable is the total weight of the box, which you should change during the course of the experiment. The dependent variable is the angle at which sliding starts. According to the theory the angle does not depend on the weight.
  5. Apr 23, 2013 #4

    Simon Bridge

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    Part of the exercise is to think your way through the experiment though ... I had hoped OP would be able to figure that out without having to be told quite so directly. Ho hum.
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