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)

x

(m)

t (s)

GRAPHING MOTION interpreting an x vs. t (position vs.

time) graph

(moving

forward)

constant +v

(not moving

)

constant v = 0

(moving backwar

d)

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

trun = t

slope = rise/run = x/t, so slope = vav

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)

graphv

(m/s)

t (s)

(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

v

(m/s)

t (s)

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/s2

speed increase (+a), speed decrease (–a), change in direction (what are the three accelerators in a car?)

average acceleration, aav = (vf-vi)/t = v/t

ACCELERATION Constant acceleration

example: a=2 m/s2 V = at D =1/2 a t2

time (s) 0 1 2 3 4 5 6

speed (m/s) 0 2 4 6 8 10 12

position (m) 0 1 4 9 16 25 36

ACCELERATION terms:

t: elapsed timexf : final position

xi: initial position

x: change in position (xf-xi)

terms:a: accelerationvav: average

velocityvf: final velocity

vi: initial velocity

v: change in velocity (vf-vi)

ACCELERATION defined

equations:a = v/t vav = x/t

vav = (vf+vi)/2

derived equations:x = ½(vf+vi)t

vf = vi + at

xf = xi + vit + ½at2

vf2 = vi

2 + 2ax

QUIZ 1.3 A train traveling 25.0 m/s begins slowing

down with an acceleration of –4.00 m/s2. 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/s2 (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 degreesN 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: 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?

Combining non linear vectors

What if the plane were to fly into a cross wind?

Ex. A plane flies North at 100 m/s and there is a 50 m/s Easterly wind. What is the plane’s net (combined) velocity?

MOTION IN A PLANE Perpendicular vectors:

vy

vx

v

2y

2x vvv

x

y1

v

vtan

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(vf+vi)t vf = vi + at

xf = xi + vit + ½at2 vf2 = vi

2 + 2ax

%ErrorO A

A

100

2vv

v ifav

tx

txx

v ifav

tv

tvv

a ifav

2y

2x vvv

x

y1

v

vtan