Is there a way to set the mass of a gameobject without using the Rigidbody component??

Questions & Answers
1

I need to set the mass of different gameobjects at the start of my program by using the input boxes in the scene, at the moment I have 2 input boxes (acceleration and mass) and a dropdown box (object type) but I do plan to add more as my project develops. All the research I’ve done states to use rigidbody but as it is project work that simulates Newtonian physics I’ve been told I can’t use the basic unity physics as it would bring down the grade of my project which is why I can’t use rigidbody. So is there anyway I can add mass to the object and also is there a way to find the centre of mass of the object without using unity’s physics engine? I don’t quite understand how the message calling system works so if that is how it should be done I’d be really appreciative if someone gave me a quick run through as I’ll have to do this for multiple inputs.

2

Well mass = force / acceleration. So simply calculate force and acceleration. Then calculate mass.

Here’s how to calculate acceleration:

//Java Implementation

var lastVelocity : Vector2;

function Update()
{
    var acceleration = (velocity - lastVelocity) / Time.deltaTime;
    lastVelocity = velocity;
}

//C# Implementation
Vector2 lastVelocity;

void Update()
{
    float acceleration = (velocity - lastVelocity) / Time.deltaTime;
    lastVelocity = velocity;
}

Not to sure how you are implementing force so I can’t give a clear answer for that. Even though that’s a way to calculate acceleration you still need velocity which so happen rigid body simulates. So you have a bit of work ahead of you.

3

Well, if you don’t use Unity’s physics system you just have to “store” the mass in one of your variables. Since you want to roll your own physics you have to keep track of an objects properties (for a rigidbody the static infomation is the mass, the center of mass, the inertia tensor as well as any form parameters like drag). Note that i talk about Rigidbodies in general, not Unity’s rigidbody component.

Simulating proper newtonian physics can be quite complicated. It’s not clear if you actually use another third party physics engine or if you actually want to roll your own. If you use a thrid party physics engine it should have means to set the mass of an object. If you roll your own, just declare a variable like

public float mass;

And assign a value. Of course in the actual equations when you calculate the required acceleration from a given force you have to use that value.

Since this seems to be “homework” i will move the question into the help room.