The direction of the friction force in a diagram of a spring on an inclined plane is contingent upon the motion of the object. If the mass is at rest, the friction force opposes any potential motion, which could be either up or down the incline depending on the spring's state (tension or compression). Without additional information regarding the spring's stretch or compression, it is impossible to definitively determine the direction of the friction force. The key takeaway is that friction always opposes relative motion between surfaces in contact.
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Danya314 said:It could point either up the incline, or down the incline.
Danya314 said:So, which is it?
or in a direction to oppose motion. (It may be at rest.)Dick said:The force of friction always points opposite the direction the object is moving.
No, it opposes relative motion of the surfaces in contact. I know that's what you meant, but expressed the way you had it can lead to confusion, e.g. when a car is going uphill.Dick said:The force of friction always points opposite the direction the object is moving.
haruspex said:No, it opposes relative motion of the surfaces in contact. I know that's what you meant, but expressed the way you had it can lead to confusion, e.g. when a car is going uphill.
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Suppose there were no friction. Which way would the block move? Is there enough information to decide?Danya314 said:So in this case, would it point down the incline?
If a block, attached to a spring, is at rest on an inclined plane and that's all the information you have, then there is not enough information to deduce the direction of the friction force. It could be up the incline or down the incline, depending on the amount by which the spring is stretched or compressed. That's why I said your statement in the "attempt at a solution" section was correct.Danya314 said:So, which is it?
You wrote that it was "on" the spring. Is it above the spring or below it on the slope?Danya314 said:If friction was ignored, then I would assume the the net force would pull the block down the incline and strech the spring.