Common Physics Misconceptions

{\rtf1\ansi\ansicpg1252\cocoartf1138\cocoasubrtf510 {\fonttbl\f0\fswiss\fcharset0 ArialMT;\f1\fswiss\fcharset0 Helvetica;} {\colortbl;\red255\green255\blue255;} \paperw12240\paperh20160\margl1440\margr1440\vieww14260\viewh17500\viewkind1 \pard\tx720\tx1440\tx2160\tx2880\tx3600\tx4320\tx5040\tx5760\tx6480\tx7200\tx7920\tx8640\pardirnatural \f0\fs28 \cf0 Imagine learning for the first eighteen years of your life that the earth is flat. All through elementary school and high school you grow up hearing about the flat earth we live on and doing boring flat-earth physics homework and then (if you're lucky enough) you get to college and PSYCH! \f1 for the first time they show you a globe and say "sorry for lying, the earth is actually round".\ \ Well, this is, unfortunately, exactly what we do with\ \ 1) Gravity\ You probably learned that objects attract each other based on their mass so you probably grew up thinking that light can't possibly be affected by gravity because light is massless. I know I did. Well guess what? The source of gravity is not mass - it's energy and momentum, which light certainly has (of course, regular matter does too). So not only does light get bent passing by a star or planet or black hole, but light attracts the planet or star or black hole in return (to be sure, it's only a very very small amount. But a small amount is not zero). Anyway, the point is that Newton's law of gravitation is just an approximation - good enough to get us to the moon, but not perfect. General relativity is better.\ \ 2) Special Relativity\ Speaking of the moon, you probably also learned that if a sheep is moving 2 mph relative to a train and that train is moving 2 mph in the same direction relative to the ground, then the sheep is moving four mph relative to the ground. 2mph+2mph=4mph, right? FALSE. Experiments in special relativity have confirmed that velocities don't simply add together and so the sheep will in fact be moving very very ever-so-slightly slower than four mph relative to the ground. And the formula that correctly predicts this deviation from just adding the velocities is (v1+v2)/(1+v1*v2/c^2). It's not a very big effect, but then again, the earth looks pretty flat, doesn't it?\ \ But the earth isn't flat: if I walk 10,000km away from my cat, and you continue on walking 10,000km more, you're NOT 20,000km away from my cat. You're just 12,750km away\'85 in fact, the farthest on earth you can get from ANYTHING on earth is 12,750km. It's the "earthly distance-limit", though we normally call it the diameter of the earth. And similarly, when you try to add two velocities together, there's a "cosmic speed limit" of 300,000,000m/s - that is, the speed of light.\ \ So, just because to our eyes the earth looks flat, velocities look like they simply add together, and light looks like it doesn't attract gravitationally, is that an excuse to mislead ourselves and our children about the true nature of things?}

Channel: minutephysics

Views: 5,628,567

Rating: 4.8428431 out of 5

Keywords: quantum, mechanics, Einstein, energy, infinite, bang, theory, cosmic, galaxy, universe, force, moon, sun, dimension, string, special, relativity, black hole, science, gravity, Neutrino, photon, General, Dark, Minutephysics, minute, physics, Henry, Reich, cat, schrodinger, Perimeter, Institute, President of the US, Barack Obama, Henry Reich, wavefunction, touch, Neil deGrasse Tyson, Neil Tyson, Purpose, God, Religion, Atheism, Atheist, Agnostic, addition of velocity, flat earth, speed of light, cosmic speed limit, mass, light

Id: IM630Z8lho8

Length: 2min 40sec (160 seconds)

Published: Thu Dec 06 2012

Reddit Comments

[u/Chumlee]

This seems shallow and pedantic. We teach these things due to the level of simplicity they add to a problem. I agree that adding a division to the velocity one is not that hard but why should we care (other than for scientific pedagogy)?

[u/tolerantlychaotic]

Interesting stuff, but I don't agree with the conclusion that we are misleading or lying to school children when we teach them this stuff.

Without getting too deep into educational theory, each child is only cognitively capable of understanding a certain limited domain-specific concept at any given developmental stage, so often they learn a simplified version of a concept only to later learn there are exceptions or additional caveats, such as the values in the video that are negligible in everyday physics calculations. Education is essentially a series of lessons, lectures, demonstrations, and discussions that slightly upset previously held knowledge/beliefs and lines of reasoning in order to establish new ones that will probably be upset again (e.g. arithmetic -> algebra -> calculus; Euclidean -> non-Euclidean geometry; Newtonian classical mechanics -> quantum and relativistic mechanics). If done well, these lessons systematically return to similar concepts year after year but in slightly expanded and more advanced form, a process sometimes called spiral curriculum.

[u/wilkeson]

pretty sure most people who have taken a high school physics class know that light is affected by gravity, cause, you know, black holes.

[u/T1LT]

As he says at 0:57: "general relativity is better". Better not perfect, both that and classical physics are just models of some of the things we know, approximations. And even relativity we know to be wrong and that it does not work in sub-atomic scales because it is a simplification and does not account for a bunch of other things.

[u/daLor4x_r]

this is an interesting video, but it claims that light is the maximum speed at which things occur. linked particles have demonstrated to interact with each other over great distances, faster than the speed of light. that is both a great mystery, and a total mind fuck.