# Use of GetLinkForce or GetLinkTorque

Hi,

In my gazebo plugin, I have to use the function

```
virtual math::Vector3 gazebo::physics::Joint::GetLinkForce ( unsigned int _index) const pure virtual
```

or

```
virtual math::Vector3 gazebo::physics::Joint::GetLinkTorque ( unsigned int _index) const pure virtual
```

These functions should return the force applied at the centre of mass of a link; the problem is that this functions are pure virtual, so I must define them. I could use the ODEJoint class (that inherits from Joint class): this owns the above functions, but only virtual.

I don't understand how to use the ODEJoint class, nay how to include this class in my plugin.

Can I use this functions without having ODEJoint?

Thank you!