Why do particles of equal mass rebound at 90 degrees?

[@niconeuman]

Very nice video. An algebraic demonstration is that if you take the dot product of the vector equation
u = v + w
with itself, you get:
u^2 = v^2 + w^2 + 2 v * u
And that can only equal the conservation of energy equation if v * u = 0, which means they are orthogonal.

[@niconeuman]

Meant v * w in the last two equations!

[@DrBenYelverton]

@@niconeuman Nice, thanks for sharing!

[@markusklyver6277]

This approach also gives the angle when the masses are not the same.

[@asthavora9046]

thank you so much!

[@mxminecraft9410]

Sir do you know of any books with very difficult classical mechanics ( especially Newton laws and kinematics) questions?

[@DrBenYelverton]

There are some old textbooks by S.L. Loney that I like, you'll find some very interesting problems in there. Over 100 years old, but not much has changed in classical mechanics since then so definitely worth a look!

[@mxminecraft9410]

@@DrBenYelverton Great coincidence I am currently solving SL Looney Trigonometry book 😃

[@DrBenYelverton]

Ah, excellent!

[@mxminecraft9410]

@@DrBenYelverton sir were u referring to SL Looney's Statics and dynamics book ?

[@DrBenYelverton]

That's one of them, there is also another called "An elementary treatise on the dynamics of a particle and of rigid bodies".

[@Inthe-way]

Thank you sir.
That really was beautiful.

[@DrBenYelverton]

Thank you!

[@mxminecraft9410]

Nice video 👍

[@markusklyver6277]

We have
u = v +w.
So
= ||v||² + ||w||² + 2.
So 2 =0, and = 0.
QED