请问unity3d编码中以下错误是什么意思？

error CS1061: Type `UnityEngine.Component' does not contain a definition for `AddForce' and no extension method `AddForce' of type `UnityEngine.Component' could be found. Are you missing an assembly reference?
你好，我给物体添加了rigidbody后，还是出现了编码错误，如下（ps：我用的是unity3d5.5.1版本） 请问是怎么回事？
error CS0120: An object reference is required to access non-static member `UnityEngine.Rigidbody.AddForce(UnityEngine.Vector3)'