Transcript class_objective_5 IPC Motion, Forces and Energy

TAKS
Objective 5
Motion , Forces
and Energy
Energy
Is defined as the ability to do
work
Mechanical energy has two
types:
Kinetic (Energy of Motion)
and
Potential (Stored Energy)
Kinetic Energy
KE = ½
2
mv
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
(spring or rubber
band)
Gravitational Potential Energy
or Will it fall?
GPE = mgh
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 cannot be created
or destroyed, but can be
changed from one form to
another
 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 heat
energy is given off than is
used to start it is
exothermic
An endothermic reaction
absorbs heat energy and
causes cooling
Electrical Energy Moving electrons in a path is
electricity



Potential energy (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) and is measured in
Ohms.
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
G.
R
It is the 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 amps
9V
=
I
x
2
ohms
D. 18.0 amps
or 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
(solids)
2. Convection- heating by
circulating fluids, (gas and
liquid) heating from a fireplace
And. . .
3. Radiation – Transfer of
Electromagnetic (E.M.)
Energy

The suns heats the earth
by sending infrared
radiation along with
other forms of E.M.
energy at a speed of
3.0 x 108 meters/second
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
F improve
emission
would be from
a solid
exteriorof–infrared
Not G radiation
the heat
losschange
by convection
currents
Painting Ga reduce
substance
will not
its conductivity
– That isHaimprove
propertyabsorption
of metals.of infrared
It wouldradiation
have to be
made ofJareduce
different
to changeproperties
that: Not J
thesubstance
heater’s conducting
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
nucleii 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/s in
space
 ROYGBIV
 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 direction 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 waves: heat
 Visible light: (ROYGBIV)
 Ultraviolet: tanning
 X-rays: medical
 Gamma rays:

Waves - Energy carried by
rhythmic disturbances



Two types:
1. Radiation
(electromagnetic
waves) move through
empty space
2. Mechanical waves
require a medium (air,
water or any type of
matter) for movement
Waves - 2 Types
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 is 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. electromagnetic waves,
waves on a slinky or rope
coil, ocean waves
LONGITUDINAL or
Compressional 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
Compression Waves
Sound is produced when a compression is
made.
It requires a source to produce the
compression and a medium for it to travel
through.
The more elastic the object, the faster
sound travels.
(The denser the medium, the faster
mechanical waves can move)
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)
Motion can be described as
a
change in an
object’s position
 Average velocity
(speed) is the
change of position
of an object over
time
Velocity Graphs
____________
Velocity
(v) is
the slope (rise
over run) of a
position (d) vs.
time (t) graph
Distance (m)
 Velocity
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
Acceleration
Velocity ((m/s)(m)

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

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
Use the ruler on the side of the
chart and the equation for velocity.
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
speed or
direction
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
 An
object
in motion
stays in
motion
Newton’s 1st Law of
Motion
And
an
object at
rest
stays at
rest
Newton’s 1st Law of
Motion
 Unless
there is an
UNBALANCED force acting
on it
Inertia or Newtons 1st Law
Tendency for an
object to stay at
rest or moving in
a straight line at
a constant speed.
 The mass
(measured in kg)
of an object
determines its
inertia

Newton’s 2nd
Law of Motion
Force = mass times 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
If you apply a force to
objects, the object with
the least mass will
have the greatest
acceleration.
Newton’s 2nd Law of Motion
 The
greater the
mass 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
WRONG!
Newton’s 3rd Law of Motion
 For
every
action there
is an equal
and opposite
reaction
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

= force out / force in
A machine can make this happen
by moving the input force
through a farther distance than
the output force
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 %
 Energy is lost due to
friction between
moving parts

Machines use
power Power: the rate at

which energy is used
(work is done)
 Power = 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 plane
 Lever
 Pulley
 Screw
 Wedge
 Wheel and axle
Universal Law of Gravitation
All objects in
the universe
attract each
other by the
force of
gravity
Universal Law of
Gravitation
Gravity varies depending
on two factors:
1) the masses of the
objects, and
2) the distance from the center
of one object to the center of
the other
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 gravity (g)
WEIGHT IS THE FORCE OF
YOUR MASS PUSHING ON
THE EARTH
 Unit of mass = kg
 Unit of acceleration = m/s/s
 Unit of weight = Newton

USE THE FORMULA PAGE
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Some of the
problems
require you to
grid in an
answer. Make
sure you pay
attention to the
decimal point in
the square in
the middle.