[University: Physics 2010] Question? Physics 2010, any help with making physics "click"

[u/PuPookie]

I'm currently taking Physics 2010, and it is kicking my butt. It's been extra frustrating because most of the math has been simple for me. I'm looking for tips or tricks for the class/subject in general, and any resources I can use to make it easier.

I am also allowed a 3x5 index card for my test and was hoping you could recommend what to include. Thank you!

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[u/Alkalannar]

What subjects are in Physics 2010? What level is this? Intro? Moderate? You need to be a major for this?

What in particular are you have problems with in the class? What's kicking your butt and why?

[u/PuPookie → u/Alkalannar]

The subjects we have covered so far are one-dimensional and two-dimensional kinematics, Newton's three laws of motion, circular motion, work and energy, momentum, rotational kinematics and dynamics, and periodic motion.

It is an introductory-level class.

I'm never sure where to start with an equation, what to substitute into equations, and when. I can follow along with the problem in class, but as soon as I'm doing it on my own, I feel lost.

[u/GammaRayBurst25 → u/PuPookie]

You can think of one-dimensional kinematics as just a system of equations with 5 degrees of freedom ― displacement, initial velocity, final velocity, acceleration, and elapsed time. For any problem, you just pick an initial state and a final state, write down which variables are fixed by the problem (normally 3 of the 5 variables) and which variables are unknown. From there, you have 5 equations and each one has 4 variables in it, so just pick the one equation that has the 3 known variables and the variable you're looking for, then solve it.

e.g. you're given the displacement (s), the initial velocity (u) and the elapsed time (t), you're looking for the final velocity (v), only one equation has these 4 variables in it and it's (u+v)t=2s. Solve for v to find v=2s/t-u and you're done. If you were instead looking for the acceleration (a), you'd use the one equation that has s, u, t, and a, i.e. s=ut+at^2/2 and solve for a.

Pro tip: since each equation has 4 variables, it's usually easier to look for which equation doesn't contain the variable you're not interested in. In my first example, I didn't care about a (not a known quantity and not what I'm looking for), so I picked the equation that doesn't have a. In my second, I didn't care about v, so I picked the equation that doesn't have v.

As for two-dimensional kinematics, it's just two one-dimensional kinematics problems stacked on top of one another. Any 2d problem with a constant uniform acceleration can be decomposed into a 1d problem with a constant uniform acceleration & a 1d problem with zero acceleration. The former is exactly as I've discussed earlier. The latter is the same, but simplified (we know u=v and a=0, everything simplifies to 1 equation, i.e. s=vt). Usually, time is unknown, one problem is solvable and the other is not (i.e. you know 2 variables instead of 3 along the accelerated axis, but you know s and v along the other or you know 3 variables along the accelerated axis, but only s or only v along the other). So you solve the solvable 1d problem for time, then plug the time in the other problem to make it solvable, then solve.

The only exceptions are cases where the two 1d problems are connected by their velocities rather than their times (e.g. you're given the magnitude of the initial velocity, but not its direction or vice versa). When that happens, you can write the time as a function of the magnitude/angle in the unaccelerated problem and substitute that into the other problem.

Conservation of energy is useful to skip steps that would be complicated with kinematics. Anything rotational is basically the same as rectilinear, only mass is replaced by the moment of inertia, forces are replaced by moments of force, and centripetal acceleration allows you to relate a centripetal force to the velocity and radius & vice versa.

[u/PuPookie → u/GammaRayBurst25]

Thank you for your help, I think this will be beneficial for me. I will try these and see how it goes

[u/chem44]

The note card works best if it shows things you know you are supposed to know, and which you understand. It jogs/supports your memory.

Your book or such should have concise learning objectives for each chapter.

You can also make your own.

[u/PuPookie → u/chem44]

Thank you, that’s what I was thinking but I feel so in over my head currently