PHYSICS UNIT 1: KINEMATICS (Describing Motion)

MOTION ALONG A LINEWhos Upside Down?

MOTION ALONG A LINEWhos Moving?

MOTION ALONG A LINEMotion: change in position of an object compared to a frame of reference (a "stationary" reference point)Measuring Motion (along a line)position, x: location with respect to the origin The origin is (x=0), unit: mdisplacement, s = Dx : change in positionDx = xf xi displacement = final position initial position

MOTION ALONG A LINEdisplacement examples

MOTION ALONG A LINEtime, t: time since motion start, unit: s (text uses Dt)velocity, v: time rate of displacement, unit: m/saverage velocity, vav = (xf-xi)/t has same +/- sign as displacement shows direction of motion along lineinstantaneous velocity, v: actual velocity at a specific point in time, slope on an x vs. t graph.at constant speed, v=vavfor changing speed, vvav

MOTION ALONG A LINESpeed: the amount of velocity S=d/t Velocity is speed and direction (+/- along a line), speed doesnt have direction. V=x/ta velocity of -24 m/s is not the same as +24 m/s (opposite directions), but both have the same speed (24 m/s).car speedometer indicates speed only; for velocity, you would need a speedometer and a compass.

SOLVING PROBLEMSProblem-Solving StrategyGiven: What information does the problem give me?Question: What is the problem asking for?Equation: What equations or principles can I use to find whats required?Solve: Figure out the answer.Check: Do the units work out correctly? Does the answer seem reasonable?

GRAPHING MOTIONinterpreting an x vs. t (position vs. time) graph(moving forward)constant +v(not moving)constant v = 0(moving backward)constant vchanging +v(speeding up)changing +v(slowing down)

GRAPHING MOTIONinterpreting an x vs. t (position vs. time) graphfor linear x vs. t graphs: rise = Dxrun = Dtslope = rise/run = Dx/Dt, so slope = vav

GRAPHING MOTIONinterpreting an x vs. t (position vs. time) graphfor curving x vs. t graphs:slope of tangent line = vinstantaneous

GRAPHING MOTIONinterpreting a v vs. t (velocity vs. time) graph(moving forward)constant +v(not moving)constant v = 0(moving backward)constant vchanging +v(speeding up)changing +v(slowing down)

GRAPHING MOTIONcomparing an x vs. t and a v vs. t graph

ACCELERATIONconstant velocityconstant acceleration

ACCELERATIONAcceleration, a: rate of change of velocityunit: (m/s)/s or m/s2speed increase (+a), speed decrease (a), change in direction (what are the three accelerators in a car?)average acceleration, aav = (v-u)/t = Dv/tinstantaneous acceleration, a: actual acceleration at a specific point in time

ACCELERATIONConstant acceleration (a = aav)example: a=2 m/s2 v t, x t2

ACCELERATIONterms:t: elapsed timexf : final positionxo: initial positions: change in position (xf-xi)terms:a: accelerationvavg: average velocityvf: final velocityu, vo: initial velocityDv: change in velocity (v-u)

ACCELERATIONdefined equations:a = Dv/t vav = Dx/t vav = (v+u)/2

derived equations: s = (v+u)t v = u + atxf = xi + ut + at2v2 = u2 + 2as

GRAPHING MOTIONinterpreting a v vs. t (velocity vs. time) graph(speeding up)constant +a(constant speed)constant a = 0(slowing down)constant aFor linear v vs. t graphs, slope = a

GRAPHING MOTIONcomparing v vs. t and a vs. t graphs

PHYSICSUNIT 1: KINEMATICS(Describing Motion)

FREE FALLFree Fall: all falling objects are constantly accelerated due to gravityacceleration due to gravity, g, is the same for all objectsuse y instead of x, up is positiveg = 9.80 m/s2 (at sea level; decreases with altitude)

FREE FALLair resistance reduces acceleration to zero over long falls; reach constant, "terminal" velocity.Why does this occur?Air resistance is proportional to v^2

PHYSICSUNIT 1: KINEMATICS(Describing Motion)

MOTION IN A PLANEStart at the Old LagoonGo 50 paces EastGo 25 Paces NorthGo 15 paces WestGo 30 paces NorthGo 20 paces SoutheastX marks the Spot!

MOTION IN A PLANETrigonometrysine: sin q = opp/hypcosine: cos q = adj/hyptangent: tan q = opp/adj

MOTION IN A PLANEVectorsscalars: only show how much (position, time, speed, mass)vectors: show how much and in what directiondisplacement, r or x : distance and directionvelocity, v : speed and directionacceleration, a: change in speed and direction

MOTION IN A PLANEVectorsarrows: velocity vector v = v (speed), q (direction) length proportional to amountdirection in map coordinates between poles, give degrees N of W, degrees S of W, etc.

MOTION IN A PLANEpuck v relative to earth = puck v relative to table + table v relative to earth

MOTION IN A PLANECombining Vectorsdraw a diagram & label the origin/axes!Collinear vectors: v1 v2 v1 v2 resultant: vnet=v1+v2 (direction: + or ) ex: A plane flies 40 m/s E into a 10 m/s W headwind. What is the net velocity?ex: A plane flies 40 m/s E with a 10 m/s E tailwind. What is the net velocity?

MOTION IN A PLANEPerpendicular vectors:resultants magnitude:resultants direction:

PHYSICSUNIT 1: KINEMATICS(Describing Motion)

UNIT 1 TEST PREVIEWConcepts Covered:motion, position, timespeed (average, instantaneous)x vs. t graphs, v vs. t graphs, a vs. t graphs vectors, scalars, displacement, velocityadding collinear & perpendicular vectorsaccelerationfree fall, air resistance

UNIT 1 TEST PREVIEWWhats On The Test:21 multiple choice, 12 problems

Dx = (vf+vi)tvf = vi + atxf = xi + vit + at2 vf2 = vi2 + 2aDx

**********************************