This applet allows learner to learn that momentum as a quantity to compare motion of different bodies. It also allows both a qualitative and quantitative understanding why Newton's 2nd law is defined by means of the change in momentum.

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since F ? d(m*v)/dt

so the graph of (m*v) versus t , the gradient is F.

perhaps you want to show with dynamics arrows the meaning of this F in relation to the (m*v) in both the simulation view and the graph view, to allow easy association of the meaning of Newton's 2nd law is defined by proportional to the change in momentum with respect to time.

good effort LeeTl, keep up the good work :)