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An Easy Question

  1. Aug 19, 2008 #1
    I'm not a physics person so hopefully this is a an easy question for you.
    Could you please explain in layman's terms?

    if an object is traveling in a straight line what is the name of the force that would move it of course ?

    i.e nudge of course with minimal effort
    if a ton object moving through the air in straight line (free fall) what is the technical term or explanation for being able to divert the objects course with MINIMAL force ...

    Love and hugs
  2. jcsd
  3. Aug 19, 2008 #2


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    F=ma, so any force, no matter how small, as long as it is greater than zero, can give the object a non-zero acceleration, moving it off course. There is no smallest force, ie. for any non-zero force, you can always find another non-zero force that is smaller. Eg. Let's say the candidate smallest force is 0.001 N. Then we can immediately say that a smaller force is 0.0001N, ad infinitum.

    However, there are times when there is a threshold or critical force. For example, an object on a surface with friction. You have to overcome the friction to move the object. The threshold or critical force needed is given by the coefficient of friction between the surface and the object, multiplied by the object's weight. Again, as long as you exceed this threshold by any amount, no matter how small, you will give the object a non-zero acceleration. 'Critical' is the generic term in physics for the value at which the behaviour of a system changes qualitatively. It's not specific to forces, so if no one has named the specific phenomenon yet, you can always say eg. critical angle, critical velocity etc. There are times when 'critical' is used to name a phenomenon, in which case it is no longer a generic term.
  4. Aug 19, 2008 #3


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    In super layman's terms any force that causes a change in speed in a direction is called acceleration, the minimal force needs to be greater than all the opposite resistive forces.
  5. Aug 19, 2008 #4


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    I'm afraid that any force fits the discription given. A 1-ton object can be deflected by changes ni the air (aerodynamic force), or by collission with another object, or by pieces of itself breaking off, even by having sunlight shining on one side of the object (electromagnetic force). Any force creates a change in course (an acceleration). In fact, that's kind of the definition of what a force is. And, the same amount of force (of any kind) coming from the same direction will produce the same amount of acceleration (deflect the object off its original course).

    Maybe "force" is the actual name you're looking for.
  6. Aug 19, 2008 #5


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    Well, I was typing while MadMike was posting, but he brings up a good point about opposite forces. If you hit the object with 5 pounds of force from the left and 5 pounds from the right, you'll get no acceleratrion, because you have a positive 5 pounds and a negative 5 pounds, which adds up to a "total force" of zero.

    So maybe "total force" is what you want.
  7. Aug 19, 2008 #6
    thanks everyone x
  8. Aug 19, 2008 #7


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    I disagree, in F=ma, although force equals acceleration, the two terms represent physically different things. The term on the left represents properties of the interacting objects. The term on the right represents the space-time motion of one of the objects.

    Suppose: A blue object 1 placed in contact with object 2 causes object 2 to move only when object 2 is red, but not blue or green. In F=ma, the left hand side will describe the redness of object 2 (as well as the colour of object 1); in contrast, the acceleration a on the right hand side describes the space-time motion of object 2.
  9. Aug 20, 2008 #8

    Well, when this happens to my wife, she calls it a "side swipe".

    My brother-in-law, the pool shark calls it a sharp "cut" in the side pocket.

    I just call it a "deflecton"
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