Physics/Introduction

Physics is the scientific study of matter (tangible, material objects with mass), energy, and the dynamics of matter & energy within the universe as we observe it. Physics is used to describe the world as we see it, predict the state of a given system in the future (and, inversely, reverse the process to predict what the starting conditions of a system were), and to ultimately create laws ("broad observations about how the universe behaves") and theories ("attempted explanations for the laws").

Physics is distinct from philosophy, in that physics and philosophy are used to solve separate classes of problems. A question a physicist might be well-suited to answer would be "If I toss a ball at a certain velocity and angle from the horizon, how far does the ball land away from me?", where a philosopher would be better suited to answer "What is the meaning of life?". Physics can be used to help aid philosophical discussion and vice versa, but very rarely do the fields overlap, simply because physics is a science.

Relationship with Mathematics

Mathematics is the best way to describe physics. The relationship between mathematics and physics is extremely close: the American physicist Richard Feynman famously described Calculus, a branch of mathematics devoted to the study of changing functions, as "The language God speaks". In learning physics, the more familiar one is with mathematics, the more fulfilling the study of physics will be to a student.

One possible course of study for the mathematics required to do physics is:

Arithmetic (addition, subtraction, multiplication, and division is foundational to the other, more interesting branches of mathematics.)
Geometry (the study of shapes and symmetry is useful for simplifying and understanding more difficult problems.)
Algebra (rearranging equations for an unknown variable lets us make useful conclusions out of incomplete information.)
Trigonometry (The study of angles, circles, and triangles. Getting to here is an excellent starting point for high school physicists.)
Calculus (The mathematics of change. Despite being a highly fulfilling academic pursuit on its own, it gets us remarkably far in understanding the rest of physics.)
Linear Algebra (solving for unknowns in a system of equations leads to vectors, then launching into applications in further studies in mathematics.)
Differential equations (The real world changes as time goes on, differential equations lets us adjust our math for these changing conditions.)
Multi-dimensional calculus
Probability and Statistics

Problem-Solving Techniques

Physics is used to solve problems. Below are some techniques used by physicists (but sometimes applicable to non-physicists) to tackle problems: suppose we are trying to solve for the position and velocities of two billiard balls after their collision.

Try a simpler version of the problem. (Example: instead of trying to solve for the final velocities of the two billiard balls given any initial angles, could we first try to solve it in one dimension by assuming the balls are held on a single line? That way, we can be better prepared to solve the full problem later, given what we have learned about the problem before. We could also ignore factors like the balls slipping on the table, the angular momentum of the balls, friction with the table, et cetera.)
Use the defining features of a problem. (Example: we know that billiard balls tend to bounce off each other, and never stick to one another. Can we use this to justify an assumption to make the math easier?)
List any equations that might be relevant. (Example: it appears that momentum and energy might be conserved, so let's start by writing those two equations: momentum is the product of mass and velocity, and kinetic energy is mass times half of velocity squared: $p=mv;T={\frac {mv^{2}}{2}}$
Seek Symmetry. (Example: if you are trying to find how two billiard balls will collide, can you ignore motion along any direction by assuming the balls won't move in the z-direction ("flying off the table")?)
Compute something (anything) to build intuition. (Example: instead of trying to find how the starting and ending momentum are related to one another, why don't we try just finding the total momentum? That might help.)
Run simulations (if possible) to build intuition. (Example: although creating a simulation of how the two billiard balls might be impractical without some coding experience, the situation is simple enough to just do experimentally. If you have two billiard balls, bouncy balls, or even marbles lying around, why don't you just try it?)
Draw pictures. (Example: what does the situation we've described even look like?)

Modern branches of physics

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There are two main theories, general relativity and quantum mechanics. General relativity deals with why things fall and quantum mechanics deal with everything else. There is also a thing called special relativity and it can be summarized like this: When things move faster, they become heavier, shorter and experience time slower, all by a factor of ${\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}$ . Energy is just that factor*mass*(speed of light)^2, and momentum is that factor*mass*speed.

General Relativity

General relativity says that things fall because the earth curves the space (and time) around it. To see why this works, get a globe. Place your left index finger where the prime meridian and the equator meet. Place your right index finger 90 degrees from your left one, keeping both on the equator. Then slowly run both hands in a straight line, heading north (running your finger represents moving time). Notice how they both collide.

The formula for how space curves is very complicated, but there is a simpler formula that predicts similar things, as long as you're nowhere near a black hole. Otherwise, you should be more focused on getting away from the black hole, if anything. The simpler, not perfectly accurate formula is here: $a={\frac {Gm}{r^{2}}}$ where a is the acceleration required to keep object at a constant distance r from a mass m.

Quantum mechanics

See also: Quantum mechanics/Introduction

Quantum mechanics describe three main forces, electromagnetism, the strong and weak nuclear force. It also suggests that the position and momentum of everything is a probability cloud, that is, that I am currently in multiple places at once and that I could move at different speeds at once. This also implies that I can change speed sporadically as the uncertainty can mean that my speed may be different in the future. Though, before you call BS on this one though, most objects (and living things) are large enough such that there is a lot of certainty about where I am and how fast I'm moving (as per $\Delta p\Delta s\geq \hbar$ ). The latter implies inertia, a phenomenon in which large things conserve momentum.

There is also another formula: $\Delta E\Delta t\geq \hbar$ : uncertainty in energy times uncertainty in time is always above some value. This means that in theory, a very high energy or high enough mass could just poof into existence like magic, but it must be gone in a short amount of time such that we can't notice it in all of the noise. This means that energy and mass are conserved, for all intents and purposes.

Context for the rest of the section:

Chemical Sciences

Electromagnetism

This word is used a lot to talk about nonsense, but trust me, quantum mechanics is not pseudoscience. Electromagnetism the force that attracts or repels two charged objects, like the electrons on my hand and those on the keyboard, allowing me to press the keys on my keyboard. It is explained by the use of photons, particles which are also responsible for sight. So when I push on one of the keys of my keyboard, the electrons in my finger and those on the keyboard exchange photons, forcing the key to go down. Thus, electromagnetism is responsible for so called 'contact forces'.

Strong Nuclear Force

The strong nuclear force is the force keeping the nuclei inside atoms together. As protons are repelled by each other, due to having the same charge, another force and new particles, one of which is the neutron (the neutron contributes to the strong nuclear force, but not to the electromagnetic repulsion) and the other is the gluon, which carries the force. So in a nucleus, the protons and neutrons exchange gluons, keeping it together, though, sometimes, it just isn't enough...

Weak Nuclear Force

The weak nuclear force is a mechanism for nuclei which don't want to exist (they're called radioactive nuclei) to not exist. Sure, sometimes they might just break apart, but other times, they use this mechanism, called beta decay. When a nucleus has had enough of life, a neutron might decide to turn into a proton and emit an electron (which will go into orbit around the atom) and a new particle called a neutrino. The weak nuclear force is exchanged by the W and Z bosons.

Test

1. Debunk the following flat earth arguments

1a. Why doesn't everything fall off if the earth is spinning?

1b. Water curves on the round earth. Doesn't water always maintain it's own level?

1c. Gravity doesn't exist, therefore it can't make the earth round. Everything falls because denser things are attracted to the earth, displacing

lighter objects.

2. Debunk the following anti-5G argument: Electromagnetic radiation, which is given by 5G, is inherently harmful.

3. Why don't nuclei fly apart?

4. How does beta decay work?

5. What do fast-moving objects do?

Test answers

1a. Gravity keeps things onto the earth, despite the fact that earth is spinning. This is a valid point, as inertia is a thing and large objects will maintain their momentum imparted by the earth, and will fly off into space. But gravity exists, fortunately.

1b. Water does not maintain it's own level. Water molecules are not magically immune to the curvature of space, explaining how water can curve around the earth.

1c. Your new model doesn't work. For example, place some lead on top of a bag of feathers. The lead doesn't pass through the feathers now, does it?

2. Electromagnetic force is transmitted by photons, aka, light. Therefore, it's rational to assume that 'electromagnetic radiation' means light. Light is not inherently harmful.

3. Nuclei don't fly apart due to the strong nuclear force.

4. Beta decay involves a neutron splitting apart due to the weak nuclear force.

5. Fast moving objects become heavier, shorter and experience time more slowly.

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