Isaac Newton's Second Law of Motion

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SVG - Scalable Vector Graphics Page

The Second Law is concerned with relating acceleration to mass and net force.

Acceleration is inversely proportional to mass.


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What to look for:

  • The applied net forces are the red arrows. In each case the force is the same. There is no consideration for changes in force in this demonstration. The applied net force is constant.
  • The yellow boxes are the masses. Although all the yellow boxes have the same size, they do not all represent the same mass. The mass is different in each case. Note the labels. The one at the top is the smallest mass, m. The one at the bottom is the largest, 3m, or three times the top mass. The one in the middle is twice as massive as the one at the top.
  • All of the objects accelerate. The velocity in each case gets greater and greater. That is, the speed increases. However, the three accelerations are not all the same. All the objects are speeding up; it's the way they are speeding up that is different.
  • The acceleration at the top is the largest acceleration. The velocity changes by the greatest amount per second here. Note that here we have the smallest mass. So the smallest mass has the largest acceleration.
  • The acceleration at the bottom is the smallest acceleration. Here the velocity changes by the least amount per second. Also, here we have the biggest mass. So the biggest mass has the smallest acceleration.
  • And the medium sized mass, in the middle, has the medium sized acceleration.
  • The middle mass has twice, or two times, the mass of the top object. The middle acceleration has one half the size of the top acceleration. The demonstration is programed that way, although this may not be apparent without measurement. So the mass changes by a factor of two (2) and the acceleration changes by a factor of one half (1/2). Those factor changes are reciprocals, or inverses, and there is demonstrated an inverse proportion between acceleration and mass.
  • At the bottom we have three (3) times the force and one third (1/3) the acceleration. Again, this is an inverse proportion between acceleration and mass, since these factor changes are reciprocals, or inverses.

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