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urp:physgen [2021-10-18] nerf_herder |
urp:physgen [2022-02-01] (current) nerf_herder [Newton's 3 laws] |
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| - | ==== General Physics ==== | + | ===== General Physics ===== |
| - | * [[#Newton's 3 laws]] | + | |
| - | * [[#Distance, time, velocity, acceleration]] | + | |
| - | * [[#Collisions]] | + | |
| - | * [[#Inclined plane]] | + | |
| - | * [[#Spring and lever]] | + | |
| - | * [[#Projectile fired at an angle]] | + | |
| - | * [[#Buoyant force]] | + | |
| - | * [[#Gravity]] | + | |
| - | * [[#Kinematics]] | + | |
| - | * [[#Miscellaneous]] | + | |
| - | ===Newton's 3 laws=== | + | ====Newton's 3 laws==== |
| 1) objects in motion stay in motion, a body at rest stays at rest, until a force is applied ("law of inertia") | 1) objects in motion stay in motion, a body at rest stays at rest, until a force is applied ("law of inertia") | ||
| 2) change in momentum of a body is equal in magnitude and direction to the force applied to it (force = mass * acceleration) | 2) change in momentum of a body is equal in magnitude and direction to the force applied to it (force = mass * acceleration) | ||
| Line 17: | Line 7: | ||
| Basic definitions: | Basic definitions: | ||
| - | * Force is in newtons or pounds. One newton = 1kg * m / s² (the force needed to accelerate 1kg at 1 m/s²) | + | * **Force** is in newtons or pounds. One newton = 1kg * m / s² (the force needed to accelerate 1kg at 1 m/s²) |
| * f = ma | * f = ma | ||
| - | * Momentum is p | + | * **Momentum** is p |
| * p = mv | * p = mv | ||
| - | * energy = work (joules) = force * distance | + | * **energy or work** (joules) = force * distance |
| * J = F*d = applying 1 newton for 1 meter (units of kg * m²/s²) | * J = F*d = applying 1 newton for 1 meter (units of kg * m²/s²) | ||
| * F = J/d | * F = J/d | ||
| + | * Work is positive if it is applied in the same direction as movement | ||
| + | * No (net) work is done moving an object horizontally some set distance (unless you overcome friction) - it does not gain or lose potential energy, or have increased kinetic energy at the conclusion | ||
| + | * **power** = work/time (joules/sec or watts) | ||
| - | Fnet = Δp / Δt (since Δv/Δtime = acceleration) | + | Fnet = Δp / Δt (since p = mv and Δv/Δtime = acceleration) |
| Change in potential energy is given by U=mgh | Change in potential energy is given by U=mgh | ||
| Line 34: | Line 27: | ||
| - | **dimensional homogeneity** - units must be correct, parts added together, left side matches right side, etc. | + | **dimensional homogeneity** - units must be correct for parts added together, left side matches right side, etc. |
| - | ===Distance, time, velocity, acceleration=== | + | ====Distance, time, velocity, acceleration==== |
| Displacement is change in position. | Displacement is change in position. | ||
| s(t) = s0 + t*(v0+vt)/2 | s(t) = s0 + t*(v0+vt)/2 | ||
| Line 48: | Line 41: | ||
| - | ===Collisions=== | + | ====Collisions==== |
| * **elastic**: Two objects bounce off each other. Kinetic energy, momentum conserved, no other energy created | * **elastic**: Two objects bounce off each other. Kinetic energy, momentum conserved, no other energy created | ||
| * **inelastic** Two objects stick to each other. Momentum conserved, kinetic energy is not conserved (some energy converted to heat, sound, etc.) | * **inelastic** Two objects stick to each other. Momentum conserved, kinetic energy is not conserved (some energy converted to heat, sound, etc.) | ||
| - | conservation of momentum: p1i + p2i = p1f + p2f | + | **coefficient of restitution** = ratio of energy conserved after collision |
| + | e = (vel. after collision) / (vel. before collision) | ||
| + | (for collision with immovable object) | ||
| + | e = (Vfa * Vfb) / (Via * Vib) | ||
| + | (for collision between objects a and b. f = final, i = initial velocity) | ||
| + | e = 1 for perfectly elastic, 0 for perfectly inelastic | ||
| + | |||
| + | **conservation of momentum**: p1i + p2i = p1f + p2f | ||
| for m1 having velocity u1 to the right, m2 initially at rest, ends with velocity v2. | for m1 having velocity u1 to the right, m2 initially at rest, ends with velocity v2. | ||
| x dimension: m1u1 = m1u2cosθ1 + m2v2cosθ2 | x dimension: m1u1 = m1u2cosθ1 + m2v2cosθ2 | ||
| Line 60: | Line 60: | ||
| Glancing blow: If and only if both masses are equal (like billiards), then the angle between the resulting vectors is always 90 degrees. | Glancing blow: If and only if both masses are equal (like billiards), then the angle between the resulting vectors is always 90 degrees. | ||
| - | ===Inclined plane=== | + | ====Inclined plane==== |
| normal force = force perpendicular to the plane | normal force = force perpendicular to the plane | ||
| - | normal force on a block resting on a slope: | + | normal force on a block resting on a slope, θ = degrees from horizontal: |
| - | f = m*g*cos(degrees from horizontal) | + | f = m*g*cos(θ) |
| parallel force = force parallel to the inclined plane | parallel force = force parallel to the inclined plane | ||
| - | it is unbalanced (objects will move down the plane), sometimes called net force | + | f = m*g*sin(θ) |
| - | f = m*g*sin(θ) | + | When parallel force > friction, it is unbalanced and objects will move down the plane |
| + | Applied force - friction = net force | ||
| + | |||
| + | ====Friction==== | ||
| + | Coefficient of friction | ||
| + | * μ = f/N (force applied divided by Normal force) | ||
| + | * fNet = fApp - Ffriction | ||
| static friction - | static friction - | ||
| Line 73: | Line 79: | ||
| N = normal force) must be overcome before the mass moves | N = normal force) must be overcome before the mass moves | ||
| μS = fs/N = m*g*sin(θ) / m*g*cos(θ) = sin(θ)/cos(θ) = tan(θ) | μS = fs/N = m*g*sin(θ) / m*g*cos(θ) = sin(θ)/cos(θ) = tan(θ) | ||
| - | kinetic friction - normal moving friction | + | kinetic friction - moving friction |
| only one type of friction applies at a time | only one type of friction applies at a time | ||
| - | ===Spring and Lever=== | ||
| - | Hooke's law: F=-kx, k=spring constant, x = displacement | ||
| - | Fulcrum: t = r * f (torque = radius * force) | + | ====Projectile fired at an angle==== |
| - | just add the torques for multiple objects on one side of a fulcrum | + | |
| - | + | ||
| - | ===Projectile fired at an angle=== | + | |
| Vx = Vo*cos(θ) | Vx = Vo*cos(θ) | ||
| Vy = Vo*sin(θ) - gt | Vy = Vo*sin(θ) - gt | ||
| Line 91: | Line 92: | ||
| y = Ax² + Bx | y = Ax² + Bx | ||
| y = -gx²/(2(VoCos(θ))²) + xtan(θ) | y = -gx²/(2(VoCos(θ))²) + xtan(θ) | ||
| - | time of flight: | + | time of flight: t = 2Vosin(θ)/g |
| - | t = 2Vosin(θ)/g | + | max height: H = (Vosin(θ))²/2g |
| - | max height: | + | distance: x = sin(2*θ)*Vo² / g |
| - | H = (Vosin(θ))²/2g | + | |
| - | distance: | + | |
| - | x = sin(2*θ)*Vo² / g | + | |
| Vo = initial velocity | Vo = initial velocity | ||
| Line 104: | Line 102: | ||
| Vf² = Vi² + 2ad ? | Vf² = Vi² + 2ad ? | ||
| - | ===Buoyant force=== | + | ====Buoyant force==== |
| pressure P = F/A (force/area) | pressure P = F/A (force/area) | ||
| + | |||
| hydrostatic gauge pressure: P = pgh, p = density of fluid, g=gravity, h=height (depth) | hydrostatic gauge pressure: P = pgh, p = density of fluid, g=gravity, h=height (depth) | ||
| + | |||
| buoyant force Fb = Fup - Fdown | buoyant force Fb = Fup - Fdown | ||
| Fb = pgVf, where Vf = volume of displaced fluid, and density * volume = mass, so | Fb = pgVf, where Vf = volume of displaced fluid, and density * volume = mass, so | ||
| Line 112: | Line 112: | ||
| => buoyant force depends on mass of displaced fluid, not the mass of the object | => buoyant force depends on mass of displaced fluid, not the mass of the object | ||
| - | ===Gravity=== | + | ====Gravity==== |
| gravitational constant between two bodies | gravitational constant between two bodies | ||
| F = G * m1 * m2 / r² | F = G * m1 * m2 / r² | ||
| Line 119: | Line 119: | ||
| - | ===Kinematics=== | + | ====Kinematics==== |
| no use of forces in the equations | no use of forces in the equations | ||
| typical equations: | typical equations: | ||
| Line 127: | Line 127: | ||
| vf = v0 + at | vf = v0 + at | ||
| - | coefficient of restitution = ratio of energy conserved after collision | ||
| - | e = (vel. after collision) / (vel. before collision) | ||
| - | (for collision with immovable object) | ||
| - | e = (Vfa * Vfb) / (Via * Vib) | ||
| - | (for collision between objects a and b. f = final, i = initial velocity) | ||
| - | e = 1 for perfectly elastic, 0 for perfectly inelastic | ||
| - | ===Miscellaneous=== | + | ====Optics==== |
| + | Refraction on going into a different medium | ||
| + | |||
| + | **Snell's law** | ||
| + | sin(θ₁) / sin(θ₂) = v₁/v₂ = n₂/n₁ (note that the n values are reversed) | ||
| + | v = velocity of light in that medium, n = index of refraction | ||
| + | v = c/n (c = speed of light in a vacuum) | ||
| + | it bends towards the normal direction when entering denser material | ||
| + | (and slows down). bend is because photons are waves. | ||
| + | |||
| + | Critical angle : smallest angle that results in total reflection, no refraction | ||
| + | θc = arcsin(n₂/n₁) | ||
| + | |||
| + | |||
| + | ====Miscellaneous==== | ||
| IV = independent variable - the variable you control, typically x axis | IV = independent variable - the variable you control, typically x axis | ||
| Line 140: | Line 148: | ||
| DV = dependent variable - the variable measured (changes because of the experiment) y axis | DV = dependent variable - the variable measured (changes because of the experiment) y axis | ||
| + | FBD = free body diagram - a drawing of mass and all the forces that are applied to it. | ||
| Back to the [[physics]] page or the [[00_start|start]] page. | Back to the [[physics]] page or the [[00_start|start]] page. | ||
urp/physgen.1634518916.txt.gz · Last modified: 2021-10-18 by nerf_herder
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