Can I move an oil tanker? Let's say that I'm standing at the edge of a basin made of concrete. This basin is filled with salt water and a ship floats on the water close to the edge of the basin. The ship is neither anchored nor does it touch the bottom of the basin with its hull.
There are no waves since the basin is closed (let's say the ship was brought in with a crane) and there's no wind.
My question is: How big a ship (in kilograms) can I move if I push against the ship? Assume that my strength is average for a mid-twenty male.
Edit: I'd like to move the ship ten centimeters. In terms of how long I'm willing to push: ten minutes.
 A: To work out the force needed to move a ship there are two considerations:


*

*the mass of the ship

*the hydrodynamic drag due to the ship's motion through the water
At low velocities the force is likely to be dominated by the mass of the ship because the drag is roughly proportional to velocity. Newton's second law tells us that the acceleration of the ship is related to the force you apply by:
$$ a = \frac{F}{m} $$
where $F$ is the force and $m$ is the mass of the ship. The distance the ship moves with time is given by the SUVAT equation:
$$ s(t) = \tfrac{1}{2}at^2 $$
and substituting for $a$ gives:
$$ s(t) = \tfrac{1}{2}\frac{F}{m}t^2 $$
So you just need to decide what movement you regard as a reasonable minimum, which determines $s$, how long you're willing to wait, which determines $t$, and how much force you can apply, which determines $F$. Then you can calculate the corresponding value of $m$.
A: Here in UK we have canals and from experience I know that a barge or a lock gate has to be pushed quite hard for some time before the object begins moving the water from one side of the object to the other.
The barge weighs nothing on water but DISPLACES X tons of water which have to be displaced to make the barge move.
A human of 150 pounds can push and eventually cause a 35,000 pound barge to move but keeping it moving will be extremely tiring - which is why barge horses were invented.
The lock gate doesn't really displace water until the gate starts moving and forces water round the opening edge of the gate.
