# Bullet impact

Quick noob question regarding bullet impact. When I fire a bullet from a gun, anything it hits just flies off into the distance. I have tried adding mass to the object being hit but it has made little/no difference.

I have been searching online for hours now looking for a basic tutorial on this. The bullet is a small cube if that makes any difference? If I shoot a huge steel box with a gun, I want it to remain stationary, but a light wooden box should move some distance.

How to I define the difference?

How does the bullet ‘fire’ from the gun? Are you adding force? How much force?

I don’t think I’m applying force. There was no mention of it in the tutorial anyway so I assume default/none. How do I apply force? The bullet is fired from the gun by the left mouse button (python script). I have an ‘empty’ ray object in front of the gun, and a cube further out as an aiming reticule. The bullet is a cube object rendered in another layer.

Again, I am a complete newbie to all this so bear with me if I appear stupid

I would double check the mass of both objects as well as the speed the projectile is traveling. The Bullet Physics engine should use simple physics equations like E = mv^2 and F=ma when resolving collisions, so the values you use for mass and speed should be similar to what you would encounter in a real life scenario if you want the simulation to give reasonable results.

Lets say the average bullet ways 1 gram and the average steel box weighs several kilograms. This means that the mass of your box should be several thousand times greater than that of the bullet.

Thanks Mobious. Follow up question. What are the weight values in blender? Mass just gives a number but what does it relate to? Is there a tutorial that you know of that I could check out? I haven’t a clue about assigning speed to an object or anything like that and internet searches are giving me very little. Thanks for the input

The masses are just in “Blender Units” which don’t have any direct relation to real units of mass. This means that you have define how much 1 unit should “weigh.” All that matters is the ratios of masses between objects anyway.

If you’re not sure about how you assign a speed to an object, then what method did you use to make the bullet move? You need to know how fast your bullet is moving If you want to get collisions right.

Ok I changed the bullet to mass of 1, the box mass of 10. The bullet moves at a speed of 150 fps set using an always actuator. This has dramatically improved the physics now. The initial problem was the bullet was assigned as a static object so had no mass defined and physics didn’t affect it. Much better now. Is this the correct method of assigning speed?