Rubiks_Kid Apr 14, 2013 at 7:00 PM Edited Apr 14, 2013 at 8:14 PM I have a ball created using Body factory and so i needed to specify density....but what if instead i wanted to specify mass primarily and have the density be calculated from the perceived "volume" (not sure how you find volume of a flat object). i have its size as radius 1/2 meter and its mass i tried setting to 1kg ( body.Mass = 1f;) ...but when i apply a force of 300N (i assume our force is in newtons) it moves about 1/4 of a meter off the ground.......1KG experiencing 9.81 m/s^2 -j gravity getting a + 300N force in the +j direction moving that little? I don't think that's right... Player inherits from Entity class directly its constructor: `````` public Player(World world, Texture2D texture, float radius) : base(world, texture, radius) { body.FixtureList[0].OnCollision += Body_OnCollision; } `````` in Game.cs `````` player = new Player(world, Content.Load("Ball"), 1/2f); player.PixelPosition = new Vector2(GraphicsDevice.Viewport.Width/2f,GraphicsDevice.Viewport.Height/2f); player.body.Friction = 1f; player.body.Mass = 1f;`````` and back in player: `````` public void Control(PlayerIndex i) { if (GamePad.GetState(i).IsConnected == true) { if (GamePad.GetState(i).IsButtonDown(Buttons.A) && hasJumped == false) { body.ApplyForce(new Vector2(0,-300f)); hasJumped = true; } body.ApplyTorque(GamePad.GetState(i).ThumbSticks.Left.X); } `````` In addition to that torque makes sense...but Force doesnt....am i missing something? do i have to specify a duration? EDIT: Don't you hate that when yu finally et around to asking it you find the answer? I was applying force during the world step dt duration..... thus 300N of force moved the object only a meter since the impulse was almost negligible... although i still don't get the update() and Step() functions....not sure how to be able to calculate how much impulse i need ... with these timesteps and so on. for a 15kg ball i figured id maybe need about 25N of constant force for 1 second tog et it to move about 1-2Meters. haven't done the math yet but not sure how with the whole world.Step(1/30f) factored in there... just set mass to 1kg, applied Linear impulse of 50N in negative y direction...it went 127M in the air from rest....this does'nt make sense :P made more calculations: with mass at 1kg Impusle: 10 15 20 25 ... 50 Displacement in Y direction: 5m 11m 20M 31 127M ???