How does Newton's Law of motion affact a submarine go???!!?

Question

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Answer 1

Newton's Laws of Motion describe only the motion of a body as a whole and are valid only for motions relative to a reference frame.
First law - An object at rest tends to stay in rest and an object in motion tends to stay in motion in a straight line at constant speed unless acted upon by an external, unbalanced force - like those big propellers.
Second law - The rate of change of momentum of a body is proportional to the resultant force acting on the body and is in the same direction. Which is why a really big submarine needs really big propellers to go.
Third law - To every action (force applied) there is an equal but opposite reaction (equal force applied in the opposite direction). So if the propeller pushes against the water one way, the propeller and the ship it is attached to move the other way.

Answer 2

Still applies, an object in motion stays in motion until acted on by an outside force. The water would be an outside force slowing and stopping the sub if it were not under propulsion.