public class SineBob : MonoBehaviour
{
    [SerializeField]
    private float strength = 1.5f;

    [SerializeField]
    private float speed = 2.0f;

    private Vector3 startingPosition;

    void Start()
    {
        startingPosition = transform.position;
    }

    void Update()
    {
        float yOffset = Mathf.Sin(Time.time * speed) * strength;
        transform.position = startingPosition + new Vector3(0.0f, yOffset, 0.0f);
    }
}