I’m a senior in high school and I don’t know how to choose sin or cos in physics problem. For the most part I memorised them. For example, why is the flux of a magnetic field = BAcos(angle) and why is the electromagnetic force = ILBsin(angle).
The last two years weren’t normal as we studied online so it’s highly appreciated if someone can eli5 and fill in the gaps for me.
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here’s what you need to know without getting too deep into math.
sin and cos are used to select out the up/down, or the left/right pieces of a particular vector. could be force, velocity, whatever. anything that is a vector. this is done because maybe you don’t care about how fast the object is moving up/down and you only care about the left/right motion.
you can quickly see which one you need with intuition. you can look at an object going down a small incline (classic first-year physics). most of the force of gravity will apply directly down to the surface (which will balance to 0 Newtons with the normal force), and a little bit of force will be directed down the incline to move the object.
you can try both sin and cos in your calculator to check which one gives you a small force or a big force. the small one will be the one going downhill, and the big one will be the one pushing directly into the plane to be balanced out with the normal force.
you should know by memory that sin of a small angle is close to 0 and cos of a small angle is close to 1.
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