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Homework Help: Free Body Diagram of a ice skater?

  1. Apr 23, 2015 #1
    1. The problem statement, all variables and given/known data
    In our science class, we had to draw a free body diagram of an ice skater. The ice skater pushes against a force plate and that results in her skating in the other direction. (Newton's third law of motion). We have to use Newton's three law of motions to explain this. Additionally, we need to draw a free body diagram about this activity. I did some researching online and I realized that in a free body diagram, you do not draw the forces exerted by the body itself. So in this example I can not draw the force the skater pushed on the force plate. So what should I draw then?

    2. Relevant equations

    3. The attempt at a solution
    Here is my explanation of the skating.
    In the first lab, the skater pushes against the force plate. By using Newton’s second law of motion, F=M*A, we can figure the amount of force the skater used to push against the wall. After plugging in the numbers, I got 12.32N. So, the skater applied 12.32N to the wall and then she glided away. This is because of Newton’s third law of motion, for every action there is an equal and opposite reaction. After the skater pushed against the wall, which is the action, there was a reaction that resulted in her gliding away. Another connection to Newton’s third law of motion is the force of gravity and it’s opposite reaction. Because of this, the skater won’t accelerate down or up. Newton’s first law of motion also applies to this situation, which explains the concept of inertia. In the beginning, the skater was standing still and she will continue to stand still unless an extra force is applied. So the 12.32N was the extra force applied for her to change her current motion. This then caused her to move and glided away.

    My current free body diagram
  2. jcsd
  3. Apr 23, 2015 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    ... there are three Newton's Laws: what are they?
    ... go to a wall and give it a good shove - really push at it! Did you feel anything push you in return?

    Off the diagram - you already know which way the skater accelerates.
    Since the force has to be in the direction of the acceleration - what does this tell you about the direction of the force?
    Since the skater accelerates, there must be a force on her. The skater cannot push on herself to make herself accelerate - so what else is in the diagram that could push on the skater?
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