# Frames of Motion

marshall4
What determines whether a boat goes upstream, downstream, or straight across?

Is it be the angle that the boat is pointed, the speed of the boat and the speed of the river?

mceddy2001
What determines whether a boat goes upstream, downstream, or straight across?

Is it be the angle that the boat is pointed, the speed of the boat and the speed of the river?

Things are reluctant to change their velocity and therefore direction. In order to start the boat moving it is going to need some force acting on it. It could be the force of the engine that got it up to speed and then when the viscous drag force of the water became equal to that of the engines thrust force it would mentain a constant speed.

Since the engine is connected to the boat, no matter which way the boat is oriented, there is going to be force pushing it in the direction the boat is pointed. To make the boat move a different direction to that in which it is pointed there must be an additional force. For instance this is the job of the rudder. As the boat travels along the water hits the rudder and bounces off it at the same angle it hit. As it bounces off the rudder it provides an equal and opposite <b>force</b>, thus modifying the resultant force of the boat. The resultant force of the boat is the direction in which the boat is traveling and can be found by adding up all the forces acting on the boat. E.g. a NorthEast force and a SouthEast force acting on a body would cause it to accelerate in an easterly direction.

In conclusion to your question the resultant of all the forces acting on the boat determine its direction.

The direction of the boat determines the Thrust force of the boat, but the force of the traveling river would have to be taken into consideration as it would modify the resultant force of the boat.

It has been an honour answering your question (wow wot a sado i must be lol) if u have any more questions, or if i u think i have missed something then please let me know. My email is mceddy2001@hotamil.com