Physics

The Beginning

Physics first appeared when an apple completely randomly decided to fall on this one guy's head.

That guy was Sir Isaac Newton, and he decided that it was weird that things fell down. He thought it was so strange that he gave the mysterious force a name. Gravity.

Newton getting hit on the head by an apple

Image Source: https://media.istockphoto.com/id/536832583/vector/isaac-newton.jpg?s=612x612&w=0&k=20&c=-MZh4DoMp6FxqrbL0qFz5v5yWcr2Chrebn4Xe8JcJRc=

Forces

Force Description
Gravity An attractive force between any two objects. Most people assume only very large objects exert gravity, but small objects exert some as well
Friction A force that opposes movement. Friction is pretty annoying because it makes perpetual motion impossible, for now, but it also makes existing possible. If there was no friction, walking would just make you fall on your face.
Normal Force The force that goes perpendicular to a surface. It keeps your coffee cup from smashing through the table, and everything on the surface of Earth from accelerating toward the fiery center of the planet.
Applied Force Applied force is the force that happens when a cat pushes a glass off the table. the cat had to apply a force to the glass in order to move it off the table
Tension Tension is the force applied by a rope or something similar to one. It can only pull, not push.
a block with arrows representing normal force, gravity, applied force, and friction

Image Source: https://math.etsu.edu/multicalc/prealpha/Chap1/Chap1-1/Example8FreeBody.jpg

A free body diagram like the one seen above is an incredibly helpful way to visualize how forces act on an object

Newton's Laws

  1. An object at rest will stay at rest and an object in motion will stay in motion moving in a straight line with constant velocity unless acted upon by an external force.
  2. Force equals mass multiplied by acceleration.
  3. Every action has an equal and opposite reaction.

Important Equations for Beginners

Equation Variables Description
v=v0+at v="velocity" v0="initial velocity" a="acceleration" t="time" One of three kinematics equations that can be used to find velocity, initial velocity, acceleration, or time given that you have the other three.
x=x0+v0t+1/2at2 x="position" x0="initial position" t="time" a="acceleration" This is also one of the three kinematics equations. It is used differently than the first one because it does not include any type of velocity, but it does require the initial and/or final positions.
v2=v02+2a(x-x0) v="velocity" v0="initial velocity" a="acceleration" x="position" x0="initial position" The final kinematics equation. This one is the only one that does not require time, so it is most useful when that is not a variable you are given.
Fg=mg Fg="force of gravity" m="mass" g="acceleration due to gravity on Earth (9.8 m/s2)" A helpful equation when making free body diagrams to measure forces on an object. Every object on Earth feels this force.
Ff=μN Ff="force of friction" μ="coefficient of friction" N="normal force" The equation that tells you how much friction there is on an object in motion. It is easy to remember because it's "FuN"!
K=1/2mv2 K="kinetic energy" m="mass" v="velocity" The equation to find the kinetic or moving energy of an object.
U=mgh U="potential energy" m="mass" g="acceleration due to gravity on Earth (9.8 m/s2)" h="height" The equation to find the potential energy of an object. Energy cannot be created or destroyed, only transfered. This equation and the one for kinetic energy often go together.