# The inclined plane paradox (proved)

• B
• migyonne
migyonne
Hello, I invite you to watch this video.
This is a simple experiment, which has never been carried out and which proves that momentum can undergo a 'repartition'...

[URL='https://youtu.be/JoM59at8cnY?si=lNA4tjiOihXwZ3U2]The Beauty of Momentum[/URL]

What do you think of this phenomenon ?
What conclusion can we draw from this?

You bounce a ball bearing moving horizontally (a) off a vertical surface mounted on a cart; then (b) off a 45° sloped surface mounted on a cart. In case (a) the ball bounces directly back, so the cart gains more momentum than in case (b) where the ball is deflected upwards but continues in the same direction as the cart moves.

There's nothing there that's novel, nor remotely unusual, let alone paradoxical.

russ_watters, Mark44, Orodruin and 1 other person
Ibix said:
There's nothing there that's novel, nor remotely unusual, let alone paradoxical.

SammyS
Thank you so much!
Do you have an experience reference or a formula, please?
It is very important for my studies

migyonne said:
Thank you so much!
Do you have an experience reference or a formula, please?
It is very important for my studies
Well, it's basic Newtonian mechanics. How much have you studied momentum and elastic (that is, ideal) collisions?

russ_watters
This should be covered in any basic mechanics class. All that is needed is the basics of inelastic collisions including a coefficient of restitution. What you want to do is to open an introductory textbook.

Mark44
It's a very messy experiment, unfortunately. In an ideal case you just need conservation of energy, momentum, and angular momentum. But because your equipment is very far from ideal (the cart is made of Duplo, if I am not mistaken) you need to worry about static and dynamic friction and other such losses. Also, your system is not closed, clearly transferring momentum to the Earth. A quantitative analysis would be challenging.

The ideal case is do-able I think, but I doubt it will come anywhere near matching what you see.

Orodruin said:
This should be covered in any basic mechanics class. All that is needed is the basics of inelastic collisions including a coefficient of restitution. What you want to do is to open an introductory textbook.
I think he more needs to study elastic collisions, like the one in his example (link), but both would be a good idea.

Nugatory
phinds said:
I think he more needs to study elastic collisions, like the one in his example (link), but both would be a good idea.
What makes you think the collisions are elastic? Just the fact that the cart jumps off the ground means it is not.

phinds
phinds said:
I think he more needs to study elastic collisions, like the one in his example (link), but both would be a good idea.
I'm with Orodruin on this one. The friction in this demo is crazy. If you can lay your hands on a Duplo cart I invite you to spin a wheel - precision engineering they are not.

Learning elastic collisions is probably something OP needs to do first, but this is very much an inelastic problem.

phinds
Ibix said:
If you can lay your hands on a Duplo cart I invite you to spin a wheel - precision engineering they are not.
As coincidence would have it, I am not unlikely to step on a Duplo cart when I make my way towards the bed shortly ...

Edit: Not a Duplo cart, but a piece of a wooden puzzle … Generally I would say not rolling without resistance is a design feature of Duplo carts. It keeps parents’ backs unbroken.

Nugatory, Ibix, phinds and 1 other person
Ibix said:
Learning elastic collisions is probably something OP needs to do first, but this is very much an inelastic problem.
It is, but I find the easiest path to understanding these problems is to analyze them in the absence of friction, then try to form an intuition for how friction changes that idealization.
(Of course that's just me, and I won't argue with anyone who prefers a different path)

Last edited:
russ_watters and phinds
What sleight of hand is needed to make this work?
migyonne said:
[URL='https://youtu.be/JoM59at8cnY?si=lNA4tjiOihXwZ3U2]The Beauty of Momentum[/URL]

Hello,
Do you want to talk about the experience or the 'truncated' video link?

sophiecentaur said:
What sleight of hand is needed to make this work?
Copy and paste the URL, deleting the question mark and everything after it.

sophiecentaur
It is missing a ’ after mentor edit. Originally it mixed up the URL and display text.

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