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Homework Help: Conceptual problems

  1. Aug 27, 2008 #1
    1. The problem statement, all variables and given/known data
    Question 1: For each of the following objects answer three questions: Does it move with constant speed? Does it move in the same direction at every instant in time? Is its motion a consequence of Newton's first law? (explain your reasoning)
    a. the golden ball on the end of a foucault pendulum
    b. a car going 50 mph on a straight road

    Question 2: List 14 interactions on a marker that has just been thrown out of someone's hand (not including when it is in the hand)?

    2. Relevant equations


    3. The attempt at a solution

    a.The pendulum does not go in a constant speed because of angle momentum and the gravitational pull brings the ball back to the center. It is a consequence of Newtons first law.
    b. The car stays at a constant speed and constant direction. However there are forces acting upon the car, so it does not go along with Newtons first law.

    Question 2: 1. friction of the air
    2. gravitational pull of the earth
    3. strong nuclear interactions of quarks and gluons
    4. electromagnetic interactions of all charged particles
    5. weak nuclear interaction of the quarks and leptons
    6. the tension between the marker lid and the marker
    7. gravitational pull of the moon
    8. . . . . . . .
  2. jcsd
  3. Aug 27, 2008 #2
    I really would appreciate it if someone would help me out. This may be very simple but it is stressing me out.
  4. Aug 27, 2008 #3
    Here are my new solutions for the first question:

    c01L1. (a) The golden ball at the end of the Foucault pendulum participates in a long-range gravitational interaction with the earth, a tension contact interaction with the string, and friction interaction with the sand and air. The gravitational pull of the earth causes the pendulum to swing back down to the center resulting in angle momentum. The friction of the sand and air also slow the pendulum down. The interaction with the string causes a constant change in the pucks direction of motion. Newton’s first law says every object continues at a constant velocity in a fixed direction unless acted upon by an external force. The ball definitely coincides with this law because the string serves as an external force to deviate the ball from the straight path that the ball would naturally follow if the string was not attached.
    (b) A car driving at 50 miles per hour along a straight part of stretch road participates in a gravitational interaction with the earth, a contact friction interaction with the air, a contact friction interaction with the road and a contact compression interaction with the road. Though the car is moving at a constant speed of 50 miles per hour and not changing direction, its motion is still a consequence of Newton’s first law. The resulting circumstances from one of the previous interactions switching off must be assessed. If only the gravitational interaction existed the car would fall down into the earth. If compression from the road only existed the car would fly into the air. However, both of these external interactions together help the car to travel at a constant speed and direction. In this situation, it would be better to read the first law as “if the sum of all forces is zero, the car will move at constant velocity”. The other external force of the engine must compensate the forces of friction and gravity for the sum to be zero. When the engine is working harder, there will be unequal forces causing an increase in speed (Newton’s Second Law).
    (c) If a baseball is thrown in deep space it will travel at a constant speed and move in the same direction at every instant in time. I am imagining that in deep space there will be no interactions with a gravitational pull or air resistance to affect the ball. This also applies to Newton’s first law because since there is no external forces present in deep space, the ball will travel at a constant velocity in a fixed direction.
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