PHYSICS UNIT 1: KINEMATICS (Describing Motion)

MOTION ALONG A LINE Who’s Upside Down?

MOTION ALONG A LINE Who’s Moving?

MOTION ALONG A LINE Motion: change in position of an object compared to a frame of reference (a "stationary" reference point) Measuring Motion (along a line) Speed is the rate at which distance is covered. Avg. speed = distance/time (m/s)

MOTION ALONG A LINE Distance, D: Distance is how far an object moves, unit: m Time, t: time since motion start, unit: s Velocity, v: is speed in a given direction Ex. 30 m/s North

MOTION ALONG A LINE Instantaneous Speed: the speed at any given instant. (This is what your speedometer reads)

SOLVING PROBLEMS Problem-Solving Strategy Given: What information does the problem give me? S = 20 m/s t = 5 s Question: What is the problem asking for? D = ? Equation: What equations or principles can I use to find what’s required? S=D/t Solve: Figure out the answer. D=Sxt = 100m Check: Do the units work out correctly? Does the answer seem reasonable?

Practice Two cars are traveling south on I-5. Car A has an average speed of 20.0 m/s. Car B has an average speed of 30.0 m/s. a. How much time does it take Car A to travel 1500 m? b. How far does Car B travel in 30.0 s? 75 s 900 m

LAB 1.1 QUIZ A student made the following graph by moving in front of a motion sensor (the student was facing the sensor). Describe the student’s motion for each labeled section. a b c d e

PHYSICS UNIT 1: KINEMATICS (Describing Motion)

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

GRAPHING MOTION interpreting an x vs. t (position vs. time) graph for linear x vs. t graphs:  rise =  x x t run =  t slope = rise/run =  x/  t, so slope = v av

GRAPHING MOTION interpreting an x vs. t (position vs. time) graph for curving x vs. t graphs: x t slope of tangent line = v

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

GRAPHING MOTION comparing an x vs. t and a v vs. t graph

PHYSICS UNIT 1: KINEMATICS (Describing Motion)

ACCELERATION constant velocity constant acceleration

ACCELERATION Acceleration, a: rate of change of velocity unit: meter per second per second or m/s 2 speed increase (+a), speed decrease (–a), change in direction (what are the three accelerators in a car?) average acceleration, a av = (v f -v i )/t =  v/t

ACCELERATION Constant acceleration example: a=2 m/s 2 V = at D =1/2 a t 2 time (s) speed (m/s ) position (m)

ACCELERATION terms: t: elapsed time x f : final position x i : initial position  x: change in position (x f -x i ) terms: a: acceleration v av : average velocity v f : final velocity v i : initial velocity  v: change in velocity (v f -v i )

ACCELERATION defined equations: a =  v/t v av =  x/t v av = (v f +v i )/2 derived equations:  x = ½(v f +v i )t v f = v i + at x f = x i + v i t + ½at 2 v f 2 = v i 2 + 2a  x

QUIZ 1.3 A train traveling 25.0 m/s begins slowing down with an acceleration of – 4.00 m/s 2. The train travels 50.0 m as it slows down (but it does NOT come to a stop). (a) What is its final velocity? (b) How much time does it take? (c) How far would the train have traveled in 5.00 s? Note: the train’s final velocity is NOT the same as it was in question (a) 15.0 m/s 2.50 s 75.0 m

PHYSICS UNIT 1: KINEMATICS (Describing Motion)

GRAPHING MOTION Free Fall: all falling objects are constantly accelerated due to gravity acceleration due to gravity, g, is the same for all objects use y instead of x, up is positive g = –9.80 m/s 2 (at sea level; decreases with altitude)

FREE FALL air resistance reduces acceleration to zero over long falls; reach constant, "terminal" velocity

PHYSICS UNIT 1: KINEMATICS (Describing Motion)

MOTION IN A PLANE Motion in a Plane vs. Motion in a Line It’s like reading a treasure map. Go 25 Paces North Go 15 paces West Go 30 paces North Go 20 paces Southeast X marks the Spot!

MOTION IN A PLANE Scalar Quantity: only shows how much size or magnitude (distance, time, speed, mass) Vector Quantity: shows how much size or magnitude and in what direction displacement, r : distance and direction velocity, v : speed and direction acceleration, a: change in speed and direction

MOTION IN A PLANE Vectors arrows: velocity vector v = v (speed),  (direction) length proportional to amount direction in map coordinates between poles, give degrees N of W, degrees S of W, etc. N S W E  v

Examples of Vectors If a plane flies North at 100 m/s and the wind blows North at 20 m/s. What is the resultant? If a plane flies North at 100 m/s and the wind blows South at 20 m/s then what is the resultant

MOTION IN A PLANE Combining Vectors draw a diagram & label the origin/axes! Collinear vectors: v 1 v 2 v 1 v 2 resultant: v net =v 1 +v 2 (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 PLANE Perpendicular vectors: resultant’s magnitude: resultant’s direction:

PHYSICS UNIT 1: KINEMATICS (Describing Motion)

UNIT 1 TEST PREVIEW Concepts Covered: motion, position, time speed (average, instantaneous) x vs. t graphs, v vs. t graphs, a vs. t graphs vectors, scalars, displacement, velocity adding collinear & perpendicular vectors acceleration free fall, air resistance

UNIT 1 TEST PREVIEW What’s On The Test: 21 multiple choice, 12 problems  x = ½(v f +v i )tv f = v i + at x f = x i + v i t + ½at 2 v f 2 = v i 2 + 2a  x