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B Multiplication of a quantity

  1. Jun 8, 2017 #1
    What is the physical meaning of multiplication when we multiply two quantities in physics to get a single quantity? Eg. Mass * acceleration = force.
    Last edited: Jun 8, 2017
  2. jcsd
  3. Jun 8, 2017 #2
    I think it's easier to understand if you focus on a simple example. Take an object going 5 m/s for 3 seconds. For each second, the object has traveled 5 meters. So over 3 seconds, the object must have traveled 15 meters (3*5=15). You can see why this would be obvious and you should be able to use that basic train of thought for more difficult problems. I hope that helps.
  4. Jun 8, 2017 #3


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    You mean like with distance = velocity * time ?
    Or area = length * width ?

    Physically you get something that has a dimension that is equal to the product of the dimensions of the individual factors.
  5. Jun 8, 2017 #4
    The multiplication, in and of itself, is not meaningful. But the quantity which is composed of the product is usually something that is conserved or easily measured.

    Consider kinetic energy: ##{1\over2}mv^2##. It is not the fact that you take half of the product of mass and the square of the velocity that is important. It is the fact that, when work is done on a free particle, it is this quantity that changes.

    Mass times velocity may be (Newtonian) momentum, but it was not the idea of the product that came first, it was the fact that, if you have a collision between two objects (without friction), it is this quantity that is conserved. It just so happens to be the afore-mentioned product.

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