# JBox2D moving dynamic object
**URL:** https://discourse.processing.org/t/jbox2d-moving-dynamic-object/14001
**Category:** Libraries
**Created:** [September 15, 2019, 3:21pm UTC](https://discourse.processing.org/t/jbox2d-moving-dynamic-object/14001 "2019-09-15T15:21:39Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@parmex](https://discourse.processing.org/u/parmex)
#### Post date: [September 15, 2019, 3:21pm UTC](https://discourse.processing.org/t/jbox2d-moving-dynamic-object/14001/1 "2019-09-15T15:21:39Z")
Hi, i am using the JBox2D library, I have a problem.
I want to use a little square that is a dynamic object and when i press A or D it moves on left and right; but if i am over the platform it fall like a normal dynamic object. How can I do this?
The movement works but when I fall from the platform the square remain at the same height.
The code I used to move the square is this:
```auto
void Display() {
float a= body.getAngle();
Vec2 pos=box2d.getBodyPixelCoord(body);
if(keyPressed && key=='d') b.speed+=1;
if(keyPressed && key=='a') b.speed-=1;
pushMatrix();
translate(pos.x+speed,pos.y);
//rotate(-a);
fill(127);
stroke(0);
strokeWeight(2);
rect(0,0,w,h);
popMatrix();
```
---
### Author:  [@Xelo](https://discourse.processing.org/u/Xelo)
#### Post date: [September 18, 2019, 5:44am UTC](https://discourse.processing.org/t/jbox2d-moving-dynamic-object/14001/2 "2019-09-18T05:44:24Z")
are you actually using jbox2d to set the speed or is speed just a variable ‘added on’ to the jbox 2d coordinates? JBox2d requires you to use functions such as `body.setLinearVelocity() and body.applyForce()` to interface with the ‘speed’ of the jbox 2d box itself.
if you are just adding the speed to the translate instead of using jbox2d:
```auto
translate(pos.x+speed,pos.y);
```
you are essentially saying: please draw the box ‘speed’ pixels horizontally from where it should be, hence itll never drop off the platform visually, nor even move horizontally according to jbox2d’s coordinates.
---
### Author:  [@parmex](https://discourse.processing.org/u/parmex)
#### Post date: [September 18, 2019, 8:02am UTC](https://discourse.processing.org/t/jbox2d-moving-dynamic-object/14001/3 "2019-09-18T08:02:25Z")
Thank you for the reply and the explanation! it worked!
I used getLInearvelocity and then I set the x component to the speed and works!