We are receptive of triangle impulse. in fact, we agree that the algorithm for curve is too complex.

The two triangles can indeed show F1 equal to F2 at the peaks of the two triangle impulse.

Only thing is if the triangle impulse is wider (maybe change the scale of the time-axis etc. ..i don't know...) then at any pt in time inside the triangle, we can show F1 will always be equal to F2. NTL always applies. This is the enduring understanding that we want to instill in our students.

[b][color=blue]we can get student to do a data analysis of the Ft graph

scale horizontal set to just before and just after the collision

as in my 2 pictures.

get the student to think about

0.60 s

0.601

0.602

0.603

.....

with these evidence data, they could conclude that the F1 = - F2 during collision, thus N1L is validated.

[/color][/b]