Transcript H - Midland ISD

TAKS
Objective 5
Motion , Forces
and Energy
Energy
Is defined as the
Ability to do Work
Energy has Two
Types: Kinetic (Energy of Motion)
and
Potential (Stored Energy)
Kinetic Energy
KE = ½ m v
2
Ex: A moving car
has the ability to
do work on the
light pole if it hits
it.
Potential Energy
2 possibilities
Gravitational PE
-Object lifted to
some height
Elastic PE - A
stretched or
compressed
object )(springs
Gravitational Potential Energy
or
Will it fall?
GPE = m g h
m is the mass of the
object in Kg,
g is the acceleration
due to gravity which is
9.8 m/s2 on earth and
h is the height in meters
Use the formula page!
PE = mgh
41 What is the
potential energy
of the rock?
A 59,900 joules
m = 95 kg g = 9.8
B
64,600
joules
2 h =
m/s
100 m
C 93,100 joules
2 x 100
95Dkg121,600
x 9.8 m/s
joules
=
93,100 joules C
Law of Conservation of
Energy



Energy can change
forms, but is never
created nor destroyed
Loss in one form =
gain in an another
form
A falling object speeds
up as it falls to the
ground; PE decreases
as KE increases. The
KE it has at impact =
the PE it had before it
fell.
Example: A falling object
speeds up as it falls to the
ground;
PE decreases as
KE increases,
the KE it has at
impact with the
ground is equal
to the PE it had
before it fell
Energy can be conserved in
Non-Mechanical forms
The chemical energy in a
battery transforms into
electrical energy
Any reaction where more
energy is given off than is
used to start it is Exergonic
An Endergonic reaction
absorbs energy and causes
cooling
Electrical Energy Moving electrons in a path is
electricity



Electrical Potential Difference (v) is measured in
Volts
The rate of moving electric charges, Electric
Current (I), is measured in Amperes
Resistance or opposition to the movement of the
energy is called Resistance (R).
Circuits – 2 types



Series circuits are
the most simple.
One (1) path for the
current to travel.
Contains an energy
source, a path, and
a load (something
for it to do, like a
lamp)
Circuits – 2 types


Parallel circuits
provide more
than one path
for the current to
travel.
Most circuits are
parallel, since if
one lamp goes
out, the others
can stay lit.
6. Which switches, if opened, will
cause the light bulb to stop
glowing?
F. Q
It isG.
theR only
H.
S
switch in
J. T
series to
both the
battery and
light.
USE THE FORMULA
SHEET!!
What is the current in a copper wire
that has a resistance of 2 ohms and is
connected to a 9 volt electrical
source?

A. 0.22 amp V = I R so,

B. 4.5 amps

C. 11.0 amps9V = I x 2 ohms or

D. 18.0 amps

4.5 amps
Thermal Energy
A body contains internal KE due
to the motion of its atoms ( they
are constantly wiggling and
jiggling)
Thermal Energy is the total
internal KE of a body
Temperature is the average KE of
a body
Heat- Transfer of
Thermal Energy
Three forms of heating:
1. Conduction-direct
contact, a pot heating
on a stove
2. Convection- heating
by circulating fluids,
heating from a fireplace
And. . .
3. Radiation – Transfer of
Electromagnetic (E.M.)
Energy
Objects are heated when
exposed to infrared radiation


The suns heats the earth by
sending infrared radiation
along with other forms of
E.M. energy 93,000,000
miles through empty space
Heat moves by conduction in
solids since the particles are
close together and vibrate. . .
43 Heat convection occurs in gases and
liquids. Heat convection does not occur in
solids because solids are unable to —
A absorb heat by vibrating
B transfer heat by fluid motion
C emit radiation by reflecting light
D exchange heat by direct contact
Solids do radiate heat to their surroundings
2 The primary way liquids and
gases transmit heat is by the
process of —
F reflection
G conduction
H radiation
J convection
Fluid heat movement
is convection. Fluid
motion occurs in
liquids and gases.
50 A solar heater uses energy from
the sun to heat water. The heater’s
panel is painted black to —
Convection is movement of heat in fluid matter, heat loss
Faimprove
emission
of–change
infrared
would
be from
a solid
exterior
Not G radiation
Painting
substance
will not
its conductivity
theofheat
loss by
– That isGareduce
property
metals.
It convection
would havecurrents
to be
infrared
radiation
made ofHa improve
differentabsorption
substanceofto
change
that: Not J
J reduce the heater’s conducting properties
Emission is giving off – we want to absorb: Not F
Nuclear Reactions
Fusion occurs when two atoms
combine to form a new element.
The sun produces all of its
energy through fusion.
Two hydrogen atoms combine
to form a Helium atom from the
great gravitational forces and
pressure in the sun’s core
Nuclear Reactions Fission
Fission is the splitting of nuclei
of large atoms such as Uranium
and Plutonium
 Produces large amounts of
infrared radiation and other
forms of E.M. Energy such as
Gamma Rays
 Currently, it is the main form of
Atomic Energy on Earth

Radiant Energy or
Electromagnetic Energy
(EM)
All radiant energy travels at 3.0 x 108 m/sec in
space (the speed of light, c)
 Velocity of a wave = wavelength x frequency
 Visible light is just one type of EM Energy

All of the forms of radiation given off
Electromagnetic
Spectrum
by vibrating electric charges
Radiation comes in the form
of vibrating or “throbbing
bundles of energy” called
photons
The frequency of the vibrating
electric charges determines
which type and how much
energy will be given off
The entire E.M. Spectrum in
order from lowest to highest
frequency
 Radio
waves: AM and
FM
 Microwaves: cooking
 Infrared: heat
 Visible: (ROYGBIV)
 Ultraviolet: tanning
 Xrays: medical
 Gamma:
Waves - Energy carried by
rhythmic disturbances in
space
Two types:
 1. E.M. radiation
move through
empty space
 2. Mechanical
require a
medium (air or
water) for
movement

All waves have similar
properties
 Frequency-
the number of vibrations
per second or the speed of the
movement of the vibrating particles
 Amplitude – the size of the movement
of the vibrating particles
 Both are controlled by the disturbance
that created the waves
Velocity of all waves v=f λ
 f-frequency
and λ is
wavelength (distance
between identical points on
two consecutive waves)
 Reflection- bounce off
barriers in regular ways
 Refraction- waves can
change direction when
speed changes
And the answer is?
J 3300 Hz
38 At 0°C sound travels through air at a speed of
330 m/s. If a sound wave is produced with a
wavelength of 0.10 m, what is the wave’s
frequency?
F 0.0033 Hz
Use the formula chart!!!
G 33 Hz
Velocity = f λ OR
H 330 Hz
J 3300 Hz
330 m/s = f x 0.10 m
Transverse Waves
 In
Transverse Waves
particles vibrate at right
angles to the direction
the wave travels.
 Ex. E. M. Waves, waves
on a slinky or rope coil,
ocean waves
Waves - 2 Types
Longitudinal or
Compress ional Waves
Vibrating particles move
back and forth along
the direction of the
wave velocity
Parts consist of
compressions and
rarefactions
Ex. Sound Waves
Sound Waves are
Compressional
Sound is produced when a
compression is made.
It requires a producer and a
medium to travel through.
The more elastic the object, the
faster sound travels.
Sound acts like other waves
 Echoes
are reflected
sound waves
 Sonar uses echoes to
judge distance to
obstructions
 Human hearing is 2020,000 Hz, below 10
Hz is infrasonic, and
above 20,000 Hz is
ultrasonic.
Sound Waves move through
matter not through empty space.
32 One tuning fork is struck and placed
next to an identical fork. The two forks
do not touch. The second tuning fork
starts to vibrate because of —
Resonance is the vibration
F interference
of another object struck by a
G the Doppler effect
wave of the correct
frequency. Since the forks
H resonance
are identical, the second
J standing waves
one receives the correct
frequency to begin vibrating.
Forces and Motion


Forces can create
changes in motion
(acceleration)
Deceleration is negative
acceleration
Motion can be described
simply
 Motion
is a
change in an
object’s position
 Average velocity
(speed) is the
change of position
of an object over
time
Velocity Graphs
distance
V=
time
 Velocity
Velocity
Distance (m)
(v) is
the slope (rise
over run) of a
position (d) vs.
time (t) graph
60
40
Series1
20
Series2
0
1 3 5 7 9 11 13 15
Time (sec)
40 The diagram represents the total travel of a
teacher on a Saturday. Which part of the trip is
made at the greatest average speed?
FQ
How do we work this one?
GR
Calculate v = d/t for each segment.
HS
J T
Acceleration Graphs
Acceleration (a) is
the slope of a
velocity (v) vs.
time (t) graph
 Plotted on a
distance vs. time
graph,
acceleration is an
exponential curve

Velocity ((m/s)(m)
Acceleration
60
40
20
0
1
3
5
7
9
Time (sec)
11
13
15
Acceleration is a change in an
objects velocity (speed or
direction)
When an object’s
speed changes over
time it is accelerating
(or decelerating)
 A = vfinal – vinitial
time
 Units for acceleration
m/s/s or m/s2

Forces
A pull or push
(or lift) that
can cause
an object to
start
moving, stop
moving or
change
direction.
Definition of a Force

A Force is a
push or a pull
Balanced Force

A force that
produces no
change in an
object’s motion
because it is
balanced by an
equal, opposite
force.
4 The picture shows the position of a ball
every 0.25 second on a photogram.
Using a ruler, determine the velocity of
the ball.
F 3.5 cm/s
G 10.5 cm/s
H 14.0 cm/s
J 28.0 cm/s
Since the version of the test you
took has the picture smaller, we all
got it wrong! The answer was H.
Measure from the center of ball 1 to the
center of ball 2 and multiply by 4.
Unbalanced
Forces
Are forces
that result in
an object’s
motion
being
changed.
+
Friction
A force that acts in a
direction opposite to the
motion of two surfaces in
contact with each other.
Friction
Friction causes an
object to slow
down and stop.
Since the amount of
energy stays
constant, the
energy becomes
heat.
Newton’s 1st Law of
Motion
 Object
in
motion
stays in
motion
Newton’s 1st Law of
Motion
And
Objects
at rest
stay at
rest
Newton’s 1st Law of
Motion
 Until
they are acted upon
by unbalanced forces.
Inertia
Tendency for an
object to stay at
rest or moving in
a straight line at
a constant speed.
 The mass (m
measured in kg)
of an object
determines its
inertia

Newton’s 2nd
Law of Motion
Force = Mass X
Acceleration
F=ma
Weight (pull of gravity) is a
commonly measured force,
calculated by F=mg, g is the
acceleration due to gravity 9.8
m/s2
Newton’s 2nd Law of Motion
The greater the
mass of an
object, the
greater the
force required
to change its
motion.
Newton’s 2nd Law of Motion
 The
greater the
acceleration of
an object, the
greater the
force required to
change its
motion.
11 The frog leaps from its resting position at the lake’s
bank onto a lily pad. If the frog has a mass of 0.5 kg
and the acceleration of the leap is 3 m/s2, what is the
force the frog exerts on the lake’s bank when
leaping?




A 0.2 N
B 0.8 N
C 1.5 N
D 6.0 N
Formula chart says F=ma, m is mass
in kg, a is acceleration in m/s2.
So, .5 kg x 3 m/s2= 1.5 N
Newton’s 3rd Law of Motion
 For
every
action force
there is an
equal and
opposite
reaction
force.
Newton’s 3rd Law of Motion
All forces come
in actionreaction pairs
Ex: feet push
backward on floor,
the floor pushes
forward on feet
27 A ball moving at 30 m/s has a
momentum of 15 kg·m/s. The mass of
the ball is —
A 45 kg
B 15 kg
C 2.0 kg
Formula Page says that
Momentum = Mass x Velocity
D 0.5 kg
So 15 kg.m/s = M x 30 m/s
solving for M it is:
Work
Work: using a force
for a distance
W= F xd
 The work done by forces on an object
= changes in energy for that object.
 Work and Energy are measured in
Joules
 1 Joule=1 Newton • meter

42 How much work is performed when a 50 kg crate is
pushed 15 m with a force of 20 N?
F 300 J
Use
the
formula
Work
=
Force
x
distance
G 750 J
H 1,000 J
Force of 20 N x 15 meters = 300 Joules
J 15,000 J
Answer:
Why use a machine?

In an ideal
(perfect)
machine the
work put into the
machine (Win) =
the work put out
by that machine
(Wout)
Machines make work
easier
The ideal mechanical advantage
of a machine (IMA) of a machine
is the number of times the output
force is larger than the input
force IMA=Fout/Fin
 A machine can only make this
happen by moving the input force
through a farther distance than
the output force


Fin • din=Fout • dout
48 The diagram shows an
electric motor lifting a 6 N
block a distance of 3 m.
The total amount of
electrical energy used by
the motor is 30 J. How
much energy does the
motor convert to heat?
F 9J
G 12 J
H 18 J
J 21 J
Work
Input =
30J done
by the
motor
Work Output =
Resistance Force x
Resistance Distance
Workout = 18J = 6N x 3m
The difference is lost as
heat due to friction, which
is 30J – 18J = 12J
Answer G
Real Machines use Energy
No real machine is
100 % efficient. i.e.
none put out more
work than is put in
 Efficiency of a
machine is work
output/work input X
100 %


Eff = Wout X 100%
W
in
Machines use
power Power: the rate at

which energy is used
(work is done)
 P=Work/time
 Power is measured in
H.P. or watts
 1 watt = 1 Joule
1 sec
45 If a force of 100 newtons was
exerted on an object and no work
was done, the object must have —
A accelerated
rapidly
B remained
motionless
C decreased its
velocity
D gained
momentum
Work = Force x Distance
Work = 0
so
Force = 100 N
0 J = 100 N x d
distance must be 0
It did not move!
6 Types of simple
machines
 Some
Simple
Machines:
 Inclined planes
 Screws
 Pulleys
 Wheel and axle
 Levers
 Wedge
Universal Law of Gravitation
All objects in
the universe
attract each
other by the
force of
gravity
Universal Law of
Gravitation
1) the mass of the object
doing the pulling, and
Gravity varies depending
on two factors:
2) the distance from the center
of that object
On Earth gravity = 9.8
m/s/s
For
every
second that an
object falls its
speed increases
by 9.8 m/s
Weight= Mass (m) X
acceleration due to gravity
(g)
 Unit
of mass = kg
 Unit of acceleration =
m/s/s
 Unit of weight = Newton
 1 Newton= about ¼
pound