physics move twitches (trembles)

Hello, faced with a very big problem of movement of an object using physics.
If the object is to push any physical way, he will move and twitch. If the object to move without physics, it will move smoothly.
move smoothly :
void Update ()
{
tr.position = new Vector3(tr.position.x + Time.deltaTime*3, tr.position.y,tr.position.z);
}

move twitch :
bool isStart = false;
void Update ()
{
if(!isStart)
{
isStart = true;...

physics move twitches (trembles)