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## Main Question or Discussion Point

Hi,

First of all, thanks for taking the time to read my post.

I have started writing my own Particle System and I'm having trouble calculating where a particle would end up over a period of time.

I have decided to use 3 foces, gravity, buoyancy and drag. I also decided to skip friction, viscosity and what else... The first two I have merged into a simple equation:

Fgravbuoy = (Mp - Mf) * g

Mp is Mass of particle (kg)

Mf is Mass of fuild displaced by particle (kg)

g is acceleration of gravity (m/s²)

Now this works quite well on its own. The problems start showing when I implement the drag force:

Fdrag = CAp(v²)/2

C is drag coefficient

A is reference area (m²)

p is density of fluid my particle is going through (kg/m^3)

v is the velocity of the object relative to the fluid (m/s)

Fdrag being always opposite of velocity.

Given all this my problem is as follows, my program is updating the particle at every 1/60th of a second, now I can go through all my calculations and update the position of my particle on the screen. But the drag equation is dependant on the velocity of my particle at a specific point in time. In other words; this particle will create this much drag at this time when going at this speed. It is not calculating the amount of accumulated drag during the 1/60th of a second period. It is only giving me the current drag AT every 1/60th of a second.

So if I run my program updating the screen at every 1/120th of a second, the particle is not ending up in the same location on the screen.

Now I have no idea what the correct thing to do here is. Does anybody have a clue?

I get the impression I need to do an integral or derivative of my drag equation and use that.

I can't remember how to do this, it's been 12 years since I touched this.

Please let me know if you have noticed any errors in my post.

Thanks a lot!

Nic

First of all, thanks for taking the time to read my post.

I have started writing my own Particle System and I'm having trouble calculating where a particle would end up over a period of time.

I have decided to use 3 foces, gravity, buoyancy and drag. I also decided to skip friction, viscosity and what else... The first two I have merged into a simple equation:

Fgravbuoy = (Mp - Mf) * g

Mp is Mass of particle (kg)

Mf is Mass of fuild displaced by particle (kg)

g is acceleration of gravity (m/s²)

Now this works quite well on its own. The problems start showing when I implement the drag force:

Fdrag = CAp(v²)/2

C is drag coefficient

A is reference area (m²)

p is density of fluid my particle is going through (kg/m^3)

v is the velocity of the object relative to the fluid (m/s)

Fdrag being always opposite of velocity.

Given all this my problem is as follows, my program is updating the particle at every 1/60th of a second, now I can go through all my calculations and update the position of my particle on the screen. But the drag equation is dependant on the velocity of my particle at a specific point in time. In other words; this particle will create this much drag at this time when going at this speed. It is not calculating the amount of accumulated drag during the 1/60th of a second period. It is only giving me the current drag AT every 1/60th of a second.

So if I run my program updating the screen at every 1/120th of a second, the particle is not ending up in the same location on the screen.

Now I have no idea what the correct thing to do here is. Does anybody have a clue?

I get the impression I need to do an integral or derivative of my drag equation and use that.

I can't remember how to do this, it's been 12 years since I touched this.

Please let me know if you have noticed any errors in my post.

Thanks a lot!

Nic