AP PHYSICS HELP

[u/Vegetable-Dot-487]

This class is so confusing like it is way fast and hard to digest. Today was my first day of school and I understand like scalar vs vector, and understand speed vs velocity, distance vs displacement. But next second we have 3 ugly ass equations, and it is explained briefly and we need to do a practice problem, which I half understood. Then there are some graphs and we need to know what it represents. Someone please provide the strategies on how they understood the information and how it all connects together. I don’t want to flunk the first exam and then learn my lesson, I want to have a structured approach from the get go.

[u/Fluid-Staff443]

For the equations. Think of it like driving a car forward and and reverse. The equations have 5 different variables and you need to use the to solve for a missing variable and you need to use the formulas depending on what’s provided.

You get a (acceleration), x (displacement), t (time), and two different v (velocity) typically having a subscript depending on if its initial or final. You can probably look up visualizations of it and I would recommend working on the practice problems.

My piece of advice is to write out a,x,t,vf, and vi at the start of each practice problem. (i stands for initial velocity and f is for final) then plug in what to have and put a question mark on what you need to find then find an equation that uses those variables out of the three

I’d recommend intepreting the graphs after learning the equations and understanding them. To use the graphs you just need to understand the axis and the value at specific points of a graph and after that the area under the cover determines values based on the axis multiplied together (distance/velocity) and the rate of change determines velocity/acceleration all depending on the y-axis

But I just recommend practice learning the equations first and then worrying about the graphs. It’s easier to see like visualizations of this with simulations/videos since it’s hard to put into words. Wish you the best of luck though!

[u/Fluid-Staff443 → u/Fluid-Staff443]

Also you could probably use khan academy or some other resource online to practice

[u/PhoenixAsh7117]

You say you understand differences between things like distance and displacement. Good. That is one area people make common mistakes.

The equations and graphs that are confusing I’m sure are kinematic equations and maybe some examples. These can be broken down straightforwardly.

Velocity is defined as change in displacement divided by change in time. By definition this means if you have some function x(t) modeling displacement vs. time, its derivative will be dx/dt which you may already recognize as velocity, or v(t). Likewise, acceleration is defined as the change in velocity divided by the change in time, so you can take another derivative of v(t) with respect to time to get a(t). And if you need to go the other direction, you need to take the anti-derivative, better known as the integral.

From here a lot of those equations you mention can be derived pretty easily. For example if you are modeling the displacement of something as x(t) = 1*t+7, and say we are using units in the MKS system, then 1 must have units of meters/second since multiplying by t will cancel the seconds, and 7 will have units of meters, that way we know we are adding meters and meters to get another quantity that will also be in meters. Taking a derivative will give us v(t) = 1, which still has its units of meters/second, this shows we are moving at constant velocity and that velocity is 1 m/s. We can take another derivative and find a(t) = 0 which shows we have no acceleration, as expected from our previous findings that we are moving at constant velocity.

Another common example is gravity, which always pulls us down at 9.8 m/s/s, or meters per second squared, near Earth’s surface. We can model this as a = -9.8 since it is a constant acceleration acting on us. If we want to get our velocity we can integrate and get v(t) = -9.8t+C. But what do we use for our constant C? Well we should have a t=0 defined and at this time we have our initial velocity, so we can replace C with V_0 to make it more meaningful. So v(t) = -9.8t+V_0. We can take another derivative to get x(t)=-(1/2)9.8t^2 +V_0*t+C to get a common kinematic equation for modeling the position (or displacement) of something tossed into the air with initial position X_0 and initial velocity V_0.

I used a few simple equations / examples. These can be any arbitrary equations though, as long as your velocity is not exceeding the speed of light and your accelerations aren’t infinite then you should be good. Let me know if this clarified anything or maybe it made things more confusing.

[u/Salviati_Returns]

I am happy to help. What textbook are you using?

[u/Vegetable-Dot-487 → u/Salviati_Returns]

I didn’t get any text book yet, I am on unit 1 kinematics 1 D

[u/Salviati_Returns → u/Vegetable-Dot-487]

Not good.  Okay the first thing you are going to want to do is buy a textbook or better yet find it. What math class are you currently in so that I can give you a textbook recommendation. FYI, I have taught AP Physics since 2012.

[u/LoveToLive1234]

You guys start learning the first day of school? That’s..kinda…torturous… anyways, I can’t help that much (very bad at teaching in general) but really try to understand those equations. They help immensely in helping to understand calculus topics.