Twin paradox...what happens to the ship? The earth bound twin looks up and sees his travelling twin moving slower inside his spaceship because he is whizzing by at some percent speed of light. But what does the motion of the ship itself looks like to the Earth bound twin? As the ship flies by the events taking place inside appear to be happening more slowly to Earth twin, but does the ship appear to move slower as it travels a greater percent speed of light? 
 A: 
does the ship appear to move slower as it travels a greater percent speed of light? 

When the ship moves faster, it appears to move faster.
When the ship travels faster and appears to travel faster, also the twin inside the ship travels faster and appears to travel faster.
If we carefully adjust the speed of the ship to be 4 km/s faster, that will surely cause the speed of the ship to 4 km/s faster, but it's not so sure that the speed of a passenger inside the ship is increased by 4 km/s.
The speed of the passenger might increase by 3.9999 km/s, or by 4.00001 km/s. Speed of the passenger does increase though.
The things that are called closing speeds are such speed-like things that decrease inside a ship whose speed increases.
Let's say a twin wants to push a button on the ship's front wall. He must chase down the button by moving forwards faster than the button moves forwards. He closes on the button at some closing speed, I guess that's where the name closing speed comes from.
closing speed = twin's speed - button's speed
A: I am referring both to this question and to a previous one ""How will the twin paradox become ... if no acceleration was ever involved?" because they are related. For clarity let's call the twin remaining on the Earth, "Terrestrial" and the one in the ship "Traveler".
In the previous question an acceleration is involved twice because 1) after Traveler leaved the Earth, his ship stops, turns backwards, and returns toward the Earth. 2) When Traveler passes by the Earth he cannot see his twin because he moves too fast. But he can drop on the Earth a box with a picture of himself. Well, but inside the ship, the box moves with the ship velocity. To let it fall on the Earth one has to DECELLERATE it, otherwise the force of gravity won't change sufficiently the box velocity, and the movement of the box will miss the Earth.
But, how to do this deceleration? Lowering the box velocity so much means to involve a tremendous energy given the almost luminal speed of the ship.
In short, how can we compare the age of the twins without involving accelerations, i.e. without reducing the velocity of one of the twins, or of some apparatus, to the other twin's velocity?
Good luck !
