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Where did the minus sign come from?
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[QUOTE="topsquark, post: 6809203, member: 46422"] I have left the vector notation off here (it messes up the LaTeX for some reason.) The vector ##F_A## has vector components ##F_{Ax}## and ##F_{Ay}##. These are vectors so they have magnitude and direction. The magnitudes of the vectors ##\mid F_A \mid = F_A##, ## \mid F_{Ax} \mid = F_{Ax}##, ## \mid F_{Ay} \mid = F_{Ay}## are just numbers, taken to be positive by convention. The x component of ##F_A## is ##F_{Ax} ( - \hat{i} )## where ##\hat{i}## is the unit vector in the +x direction. The negative is attached to the unit vector direction, not the magnitude. It is simpler in 1D to just call the components of a vector positive and negative, but it's sloppy and not is not clearly covered in Physics classes. Heck, it wasn't covered clearly in my Math classes, either. But the concept is the same... vectors are never positive or negative. Their [I]components[/I] can [I]point[/I] in positive and negative directions. This distinction is critical when doing vectors in more than 1D. -Dan [/QUOTE]
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Where did the minus sign come from?
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