# eli5: Could the average person, in the perfect conditions, push a container ship sitting on water, any distance?

901 views

A friend and I have been having an ongoing debate for years. We were at a pub on a wharf, watching shipping container ships and cruise ships come into dock, and he posed the question. With no wind, no waves, perfect conditions, could he move the ship at all?

In: Planetary Science

Assuming drag does not COMPLETELY stop the ship, which I feel is a reasonable assumption given that ships are built to move, then yes. Technically. It would be *mind bogglingly slow*, but yes. The ship would have so much inertia that you’d probably need scientific instruments to measure its movement, but there is no such thing as an immoveable object, so a very small force on a very big object produces a very very tiny acceleration.

Ideally, you’d want ropes and one hell of a pully system with like a 1,000,000:1 mechanical advantage. You’d have to pull a rope for a few miles to move the ship a couple of inches, but you could definitely do it.

Not likely.

Water still has friction resistance that needs to be overcome. Think of it this way, if you replaced the water with honey, would you expect to move it? The water moves very easily compared to honey, but still has friction. You have to push the water out of the way in the front, overcome the drag on the sides/bottom, and over come the suction to the rear as the ship moves forward and leaves a gap (very, very, tiny) the water has to move in to fill.

If you put the ship into space with no resistive medium you would be able to start it moving very, very, very slowly.

In theory you should be able to do this. Although it would take quite a bit of effort until you even got a noticeable movement. This would be similar to how people demonstrate pulling loaded trains, but a ship would have a lot more momentum but lower resting resistance. Top Gear also did something similar to this by pulling a 13,000 tonne freight ship with a small Citroen C3 compact car. The issues they had with the tiny bit of breeze shows that this would most likely be impossible to do in practice with a human but in theory there is nothing preventing it from being done in absolutely ideal conditions.

Drag force scales with velocity at all speeds, so if the ship is *completely* stationary (just to be clear, this is a “spherical cow in vacuum” kind of scenario, the ship will never be that still IRL), the drag is zero and you can push the ship. Reeeaaaaallyyyy slowly, though.

Assuming no water resistance
.
150.000.000kg vs 75kg to start moving this at 1m/s it will take 150m/75=2.000.000 times the energy as you not pushing this weight.

On top of that you have to push the water in front of the ship away… So yeah no measurable movement at all.

Without wind, yes. You only have to overcome inertia and viscous drag which can be small if you propose acceleration/velocity to be really small.

With wind in picture, hell no if you have to fight against it.

Yes, it would. If you throw a ball to someone, that action would have a small but calculable change in the earth’s rotation. It would be vanishingly small, but real.

The same with the boat. It would be extremely tiny, but the force you applied would have a calculable and measurable impact on the boat.

Any distance? Of course. If it’s completely stationary it could be moved a few planc lengths by breathing on it a little bit, probably.