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

Impulse and Momentum, their unit and relationship

  1. Sep 17, 2011 #1
    1. The problem statement, all variables and given/known data

    Impulse is defined as: force x time

    a) Find its unit expressed in term of the base units.
    b) What quantity has the same unit?
    What could it mean? (Impulse = change in momentum)

    2. Relevant equations

    I = F x T
    P = mv

    3. The attempt at a solution

    a) First, we convert the force into its base unit, and then we solve.

    I = F x T
    = ML/T^2 x T = ML/T

    b) L/T is v so

    [F x T] = [mv]
    [Impulse] = [Momentum]

    Therefore, momentum has the same unit as impulse.

    My problem is with the second part of question b. I know without the hint given in parenthesis that impulse and momentum are related, but what is it that they want me to explain? I found the question "What could it mean?" very vague, and I don't really know how I am supposed to answer it.
  2. jcsd
  3. Sep 17, 2011 #2


    User Avatar
    Homework Helper

    Perhaps they are getting at the idea that the value you get for Impulse, is the value of the change in momentum.
    ie impulse is not the same thing as momentum, but the "amount" of impulse certainly equals the "amount" by which the momentum changes - which is why they have the same units.
  4. Oct 15, 2012 #3
    Impulse and momentum have same unit means that two different physical quantities can have the same units ALTHOUGH THEY HAVE DIFFERENT NATURE.We can only differentiate between two physical quantities HAVING SAME UNIT ALTHOUGH DIFFERENT NATURE ONLY BY THE WAY IN WHICH THEY ARE DEFINED OR ON WHICH OTHER PHYSICAL QUANTITIES THEY DEPEND ON . For example:

    Impulse is defined as------- Force*time or we can say it depends on two physical
    quantities(by definition) ,that is, force and time whereas

    Momentum is defined as ----------Mass*velocity or we can say it depends on two physical quantities(by definition),that is,mass and velocity. Thus,these two have different nature
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook