# Rigid Body Physics

## Main Question or Discussion Point

Hi, im new to these forums so i hope im putting this in the right place...

I am completely lost with how to even start a simple box on plane physics simulation. Ive read dozens of formulas and tutorials, I understand them mostly but they all seem very abstract in the sense of how to use the information they provide. Say i had a box, over top of 2 platforms like the image in the attachment. Starting from absolute ground zero, no set anything, just a blank picture, what must be calculated in order to get the box moving initially, fall ontothe ledge and calculate rotation, and do everything it should do? Please dont say to do more research or take a course because Ive been through grade 11 and 12 physics and read dozens of formulas and tutorials on rigid body dynamics but theyre all so abstract that I just cant get useful information out of them. Please help me, I am so lost on this topic and have spent weeks researching it without breaking any ground

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Dale
Mentor
Have you read about Newton's laws and their rotational equivalents? Basically, you will need to keep track of your box's position, velocity, angle, and rotational speed. Then the box will be acted on by forces and torques. At each point in time you use the force and torque to update the velocity and rotational speed, and you use the velocity and rotational speed to update the position and angle.

i would suggest that you try and look into spring based solutions. they are often easier to implement and are also very scalable. You could treat the box as a few springs with high spring coefficient (giving illusion of rigidness), and just use verlet integration scheme to move it around.

Astronuc
Staff Emeritus
It's difficult to help one without knowing one's experience.

With regard to the given problem is the box initially at rest and then released, in which case it has no initial vertical velocity, and one simply calculates the motion of the box in free fall.

This might be useful - http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html

and

http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html
http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html
http://hyperphysics.phy-astr.gsu.edu/hbase/inecon.html

When the box interacts with a solid surface, there will be an impulse reaction, so one needs to know the moment of inertia of box, the impulse load/force and the moment arm.

The box the rotates and falls untils it hits the second surface, so there is both rectilinear motion (free fall) and rotational motion.