# How to find acceleration given position and velocity? [closed]

Sorry for this very simple question but I am still very new to the laws of motion.

I am dealing with 2-dimensional vectors in my programming environment and I'm following these slides to learn about simple integrators.

Near the end of the slides for the 4th Order Runge Kutta Integrator he is calculating acceleration like this:

a2 = acceleration(p2, v2)


However, I'm not quite sure where that function is defined in the slides. I'm sure the answer is very simple but for all prior slides the acceleration was always constant.

## closed as off-topic by Qmechanic♦Jul 9 '13 at 20:30

• This question does not appear to be about physics within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

• – Qmechanic Mar 10 '12 at 17:40
• You may be interested in gamedev.stackexchange.com as well. – Manishearth Mar 11 '12 at 1:06
• This question appears to be off-topic because it is seems to more about software than physics. – Qmechanic Jul 9 '13 at 20:30

That function is not defined there because you want to use a different one, depending on what kind of motion you're modelling. Using the obvious Newton law $$a \propto F,$$ you can think of it as calculating the force that acts on your object, e.g. the spring force. In the case of gravitation, you simply put in the constant gravity acceleration downwards.
• Proportionality. You can also write $F=m\cdot a$, with $m$ constant. – leftaroundabout Mar 10 '12 at 17:59