I have a **rigid body** with with an absolute **constant force** (100, 0, 0). I am trying to predict the next position of the rigid body. The mass is equal to 1 so the constant force and the acceleration are the same.

According to Wikipedia the end displacement **s** should be

```
s = s0 + v0 * t + a0 * t * t / 2;
```

where **s0**, **v0** and **a0** are the initial displacement, velocity and acceleration. And **t** is the time interval (Time.fixedDeltaTime in Unity).

For some reason the correct displacement formula in Unity is

```
s = s0 + v0 * t + a0 * t * t;
```

I am trying to figure out **why**. I’ve tested this using a simple script with a FixedUpdate() method which logs the current position to the console.

```
Vector2 s0 = transform.position;
Vector2 v0 = rigidbody.velocity;
Vector2 a0 = constantForce.force;
float dt = Time.fixedDeltaTime;
Vector2 dsV = dt * v0;
Vector2 dsA = 1.0f * dt * dt * a0;
Vector2 s1 = s0 + dsV + dsA;
Debug.Log("DSIP X: " + s0.x + " + " + dsV.x + " + " + dsA.x + " = " + s1.x + " @ " + Time.time);
```