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Negative mass

  1. Dec 2, 2016 #1
    I'm in Physics 1 and this is an extra credit I need
    1. The problem statement, all variables and given/known data

    From time to time, it is amusing to consider extending physics to unusual circumstances or values of parameters. Consider an object with a negative mass. How would it behave? How would we be able to detect it if it exists?
    Let’s start with Newton’s second law. If a force F is applied to an object with mass –m, what would be the acceleration, including direction?
    a =
    So, in order to accelerate the negative mass object forward, you should apply a force in what direction? How would the object behave if released in a gravity field, such as that near the Earth’s surface? Keep 2 things in mind:
    1) For objects with positive mass, how does the gravitational acceleration depend on the mass?
    2) Using Newton’s law of gravitation, determine the gravitational force the negative mass object.
    3) Now determine the acceleration of the negative mass caused by the force in 2.
    2. Relevant equations

    3. The attempt at a solution
    if mass is -m, then acceleration would still be positive, right? or does force always have to be a positive?
    1. wouldn't it be the same as normal mass, but the force would be in the opposite direction?
    2.It'll be the same as normal, but the force would be negative since the mass in negative, right?
    3. since the force is going to be negative, the acceleration would be positive, so it's normal acceleration
  2. jcsd
  3. Dec 2, 2016 #2


    Staff: Mentor

    Think about F=ma with respect to gravity, for a positive mass the object accelerates downward in the same direction as the force of gravity.

    So what would happen if the mass were negative?
  4. Dec 2, 2016 #3


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    Staff: Mentor

    (1) is about positive masses only.

    (2) Where did you use Newton's law of gravity? I don't see it written down.
  5. Dec 3, 2016 #4
    oh, so it would be pushed up since gravity accel is negative, right?

    2. I just think about it, since all the variable in the equation is positive, and the negative mass is the only negative, so the force would end up being negative, right?
  6. Dec 3, 2016 #5


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    Staff: Mentor

    Start with (2) before going to (3). Jumping to conclusions before looking at the equations doesn't work.


    Going to (3), what does F=ma predict if mass and force are both negative?
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