Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why Multiply?

  1. May 9, 2012 #1
    Why F = m * a?

    Why not F = m + a?
     
  2. jcsd
  3. May 9, 2012 #2

    Integral

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Adding acceleration and mass is just like adding apples and oranges, it can't be done.

    Look at the units involved and combine them in a manner which makes sense.
     
  4. May 9, 2012 #3

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Of course, it would be (mathematically) possible to have something like [itex]F= C_1mz+ C_2a[/itex] where [itex]C_1[/itex] and [itex]C_2[/itex] are constants with the correct units ([itex]C_1[/itex] would have to have units of "Newtons per kg" or "meters per second squared" and [itex]C_2[/itex] has units of "Newtons-seconds square per meter" or "kilograms".

    But the only good Physics explanation as to why a specific formula is true is "that is what the experimental evidence shows".
     
  5. May 9, 2012 #4
    From: http://en.wikipedia.org/wiki/Newton's_laws_of_motion

    "Newton's original Latin reads:
    Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur.
    This was translated quite closely in Motte's 1729 translation as:
    Law II: The alteration of motion is ever proportional to the motive force impress'd; and is made in the direction of the right line in which that force is impress'd."
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Why Multiply?
  1. Why in Mech. Engg? (Replies: 2)

Loading...