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Easy Java Simulations (2001- ) => Questions related to EJS => Topic started by: lookang on March 13, 2012, 02:01:30 pm



Title: Physics of collision showing forces at event for 1 dimension
Post by: lookang on March 13, 2012, 02:01:30 pm
Dear Prof Hwang,

Ease of changing your own code:
reference:
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1435.msg8223#msg8223
This model is very similar to my own collision model,  i wish to study your implementation of contact forces inside your model.


My intent:

i am trying to change my own collision model http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=831.0 to include accurately the forces during impact.

Problem:

my implementation is flawed with this in-correct physics and i wish to get your help on this matter.
notice in the attachment pictures
t = 0 to t =  t_collision  = 0.295, momentum1 = m1*u1 = 8, Momentum2 = m2*u2, contact force = 0
t = t_collision+ dt = 0.30,  momentum1 = m1*v1 = -4 , Momentum2 =not shown, contact force = maximum = -800
t = t_collision+ 2*dt to t_end of simulation,  momentum1 = m1*v1 = -4 , Momentum2 = m2*v2 = not shown, contact force = 0
notice the physics (RED) is wrong, can you help make your model show contact forces correctly? I can study your model to learn :)



My Plan A:
my plan is to split the event handler into 2 parts,
t = 0 to t =  t_collision, momentum1 = m1*u1 = , Momentum2 = m2*u2, contact force = 0
t = t_collision+ dt,  momentum1 = (some midpoint to be calculated )  , Momentum2 = (some midpoint to be calculated), contact force = maximum
t = t_collision+ 2*dt to t_end of simulation,  momentum1 = m1*v1, Momentum2 = m2*v2, contact force = 0
but i don't' know how to start the solution :)


Possible Plan B:
could be squeezing at peak force to show at  t = t_collision+ dt/2
but i don't' know how to start the solution :) Is there a way to create a dt/2 inside the event?




My request:

can you demonstrate what you would do in your own model here http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1435.msg8223#msg8223
You can implement the inclusion of contact forces whichever way you feel is correct physics, i will try to understand it!



Title: Re: Physics of collision showing forces at event for 1 dimension
Post by: Fu-Kwun Hwang on March 13, 2012, 10:41:18 pm
There is no way to find the force between two objects (when they collide with each other) without further information.
e.g. model for interaction between object when they collide.

You are welcomed to check out Simulate 1D collision with a virtual spring (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=193.0). A spring is used to model the collision process(spring constant depends on the softness of both objects).