Conceptual Physics Notes on Chapter 2 Motion in One Direction.

Conceptual Conceptual PhysicsPhysics

Notes on Chapter 2Notes on Chapter 2

Motion in Motion in

One DirectionOne Direction

Conceptual PhysicsConceptual Physics Chapter 2 Chapter 2 HOW HOW FASTFAST

MotionMotion in one plane / direction in one plane / direction

Motion is relative! Motion is relative! – relative to the Earth, Sun, Galaxy, Universerelative to the Earth, Sun, Galaxy, Universe

All moving objects have All moving objects have speedspeed

Speed is a measure of Speed is a measure of how fast something is how fast something is movingmoving or or rate in which rate in which distance is covereddistance is covered

Conceptual Physics Conceptual Physics Chapter 2 Chapter 2 HOW HOW FASTFAST

Speed Speed is defined as the is defined as the distance distance covered per unit of time.covered per unit of time.

Two types of speed: Two types of speed:

AverageAverage & & InstantaneousInstantaneous– Average speed is the Average speed is the total distance total distance

covered divided by total time covered divided by total time intervalinterval

– Instantaneous speed is the Instantaneous speed is the speed speed you are going at any given timeyou are going at any given time


VelocityVelocity

VelocityVelocity is speed in is speed in a given directiona given direction

– SpeedSpeed & & VelocityVelocity are are different in Physicsdifferent in Physics


EquationEquation

vv == d d // tt

vv = speed or velocity = speed or velocity

dd = distance = distance

tt = time = time

UnitsUnits

m/s km/s mm/sm/s km/s mm/s

metersmeters

secondsseconds


EXAMPLE:EXAMPLE:

If a cheetah can If a cheetah can run a constant speed of 25 m/srun a constant speed of 25 m/s, , how farhow far will it run will it run in 10 secondsin 10 seconds??

vv = 25 m/s = 25 m/sdd = ? = ?tt = 10 s = 10 s

vv == dd // t t

((25 m/s25 m/s) = ) = dd / ( / (10 s10 s))

((25 m/s25 m/s)()(10 s10 s) = ) = dd

d d = = 250 m250 m


Constant velocityConstant velocity vs vs Changing Changing velocityvelocity

Constant velocityConstant velocity is constant speed is constant speed and directionand direction

Changing velocityChanging velocity is changing EITHER is changing EITHER speed or directionspeed or direction


EXAMPLE:EXAMPLE:The speedometer in a moving southward The speedometer in a moving southward car reads 60 km/hr. It passes another car car reads 60 km/hr. It passes another car moving northward at 60 km/hr. moving northward at 60 km/hr.

Do both cars have Do both cars have

the same speed?the same speed?

Do they have the Do they have the

same velocity?same velocity?


AccelerationAcceleration is the is the rate rate

in which velocity in which velocity changes with time.changes with time.

a = Δ v / ta = Δ v / t

Δ means Δ means a change ina change in

UnitsUnits

Δ v = m/sΔ v = m/s t = secondst = seconds a = m/s/s or a = m/s/s or

m/sm/s22

AcceleratioAccelerationn


EXAMPLE:EXAMPLE:

Pg 16 Pg 16 Question #2Question #2

Conceptual PhysicsConceptual Physics Chapter 2 Chapter 2 HOW HOW FARFAR

Free Fall : How Far?Free Fall : How Far? Gravity causes objects to fall and Gravity causes objects to fall and

accelerate toward the Earth. Such accelerate toward the Earth. Such objects are said to be in objects are said to be in FREE FALLFREE FALL..

Gravity is 9.8 m/sGravity is 9.8 m/s22

We will use 10 m/sWe will use 10 m/s22


Recall objects let go start at rest or ZERO Recall objects let go start at rest or ZERO velocityvelocity

a = Δv / ta = Δv / t Δv = atΔv = atif the acceleration is toward the earth, if the acceleration is toward the earth,

a = g : a = g : g is gravityg is gravity which is equal to which is equal to 10 m/s10 m/s22

Δv = Δv = ggtt


EXAMPLE:EXAMPLE: What would the What would the

speed bespeed be of a rock of a rock be be after 4.5 secafter 4.5 sec after it is after it is dropped dropped from restfrom rest??

After After 8 sec8 sec.?.? After After 15 sec15 sec.?.?

SOLUTION:SOLUTION:

vv = g = gtt

v = (10 m/s/s)(4.5 s) = 45 m/sv = (10 m/s/s)(4.5 s) = 45 m/s

v = (10 m/s/s)(8 s) = 80 m/sv = (10 m/s/s)(8 s) = 80 m/s

v = (10 m/s/s)(15 s) =150 m/sv = (10 m/s/s)(15 s) =150 m/s


We are trying to find a distance a object falls We are trying to find a distance a object falls and the average of that fall. Remember we and the average of that fall. Remember we drop a(n) object from rest! drop a(n) object from rest!

So we take the start velocity and the end So we take the start velocity and the end velocity and divide by two (2)velocity and divide by two (2)

dd == vvtt but but v = v = gtgt from above from above

dd = = ((gg/2/2 tt))tt or or

d = ½ gtd = ½ gt22


Example:Example: A apple drops from a tree A apple drops from a tree

and hits the ground in one and hits the ground in one second.second.

What was the speed at What was the speed at impact? impact?

What was the distance the What was the distance the apple fell? apple fell?

What if the apple fell for 3 What if the apple fell for 3 seconds, how far above seconds, how far above the ground was the apple?the ground was the apple?


Air ResistanceAir ResistanceIn the absence of air, ALL objects fall at In the absence of air, ALL objects fall at the same rate here on Earththe same rate here on Earth

g =g = 10 m/s10 m/s22

Conceptual Physics Notes on Chapter 2 Motion in One Direction.

Documents

Transcript of Conceptual Physics Notes on Chapter 2 Motion in One Direction.