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AHSGE Review
J. Pollock
Spring 2007
Physics Concepts
What are metric units for
distance?
 Distance
is measured in meters.
 Prefixes can be used for larger or
smaller numbers.
 Metric conversions of distance can be
accomplished using a chart to show
decimal movement.
 Click for metric conversion chart.
What are units of time?
 Time
is measured in seconds.
 Prefixes can also be used to adjust for
larger and smaller times.
 Time is a factor in many physical
science calculations, including speed,
velocity, and acceleration.
What is velocity?
 Velocity
is the speed and direction of
motion.
 The formula is velocity = distance 
time.
 Velocity is important for reporting
changes in position.
How is velocity related to
distance, time, and direction?
 Velocity
describes the length of time of
motion, how far an object has traveled,
and in what direction.
 An example follows on the next slide.
 Velocity is inversely proportional
(opposite) to distance and directly
(same) proportional to time.
How do I read a velocity or
distance vs. time graph?
 A velocity
graph will show time as the
independent variable (x-axis).
 Distance will be the dependent variable
(y-axis).
 Velocity can be read as the slope of the
graph where the two axes create points
on a line.
Velocity v. Time Graph
Distance (m)
Velocity Graph
15
10
5
0
Series1
Series2
0
1
2
3
Time (s)
4
5
How are velocity problems
solved?
 Velocity
problems are solved by
identifying the distance traveled and the
time it takes to travel that distance.
 The values for time and distance are
substituted into the equation for density.
 See next slide for example.
Velocity Example Calculation

Metal stakes are sometimes placed in
glaciers to help measure a glacier’s
movement. For several days in 1936,
Alaska’s Black Rapids glacier surged as
swiftly as 89 m per day (86400 s) down the
valley. Find the glacier’s velocity in meters
per second. Remember; velocity includes the
direction of motion.
 V = d/t
 V = 89 m / 86400 s
 V = 1.0 X 10-3 m/s down the valley
What is acceleration?
 Acceleration
is any change in velocity.
 It can reflect a change in speed or
direction.
 The formula is acceleration = (final
velocity – initial velocity) ÷ time.
 It can be written a = v/t.
How is acceleration related to
velocity and time?
 Acceleration
is inversely proportional to
velocity.
 It is directly proportional to time.
 Velocity can be positive or negative,
depending on whether the object
speeds up or slows down and the
direction in which it is moving.
How are acceleration
problems solved?
 Acceleration
problems are solved by
determining the values for velocity and
time.
 The values are then substituted into the
equation for acceleration.
 A = v/t
Velocity Example Calculation
 A flowerpot
falls off a second-story
windowsill. The flowerpot starts from
rest and this the sidewalk 1.5 s later
with a velocity of 14.7 m/s. Find the
average acceleration of the flowerpot.
 A = v/t
 A = (14.7-0) / 1.5
 A = 9.8 m/s2
What is force?

Force is the cause of acceleration, or change
in an object’s velocity.
 Basically, it is what causes an object to move.
 Force is related to the mass of an object.
 Balanced forces mean that all forces acting
on an object combine to produce a net force
of zero.
 Unbalanced forces mean that there is a
greater push or pull in one direction.
How is force related to mass
and acceleration?
 Force
is the product of mass and
acceleration.
 The equation is force = mass X
acceleration.
 An increase in either variable will
increase force.
 Newton’s three Law of Motion apply to
forces.
How are force problems
solved?
 The
acceleration and mass of an object
must be determined and substituted into
the equation.
 F = ma
 See the next slide for an example.
Force Example Calculation

Zookeepers lift a stretcher that holds a
sedated lion. The total mass of the lion and
stretcher is 175 kg, and the lion’s upward
acceleration is 0.657 m/s2. What is the
unbalanced force necessary to produce this
acceleration of the lion and the stretcher?
 F = ma
 F = 175 X 0.657
 F = 115 N
What is gravity?
 Gravity
is the attraction between two
particles of matter due to their mass.
 Every object exerts a gravitational force
on every other object.
 The force of gravity changes according
to mass and the distance that separates
the objects.
What are action-reaction
forces?
 Action-reaction
forces are applied to
different object.
 They occur in pairs.
 Actions are always equal and opposite
to reaction forces.
 It is not balanced forces because two
different forces are involved.
What is inertia?
 Inertia
is the tendency of an object at
rest to remain at rest or, if moving, to
continue moving with a constant
velocity.
 Every object has inertia because
objects resist changes in motion.
 More massive objects have greater
inertia.
What is momentum?
 Momentum
is a quality hat results from
an object’s mass and velocity.
 The equation is momentum = mass X
velocity.
 Momentum also has a direction.
 Greater mass means greater
momentum.
Momentum Example Calculation
 Calculate
the momentum of a 6.00 kg
bowling ball moving at 10.0 m/s down
the alley.
 P = mv
 P = 6.00 X 10.0
 P = 60.0 kgm/s down the alley
What is friction?

Friction is the force between two objects in
contact that opposes the motion of either
object.
 Friction is always opposite to the motion of
the object.
 Because of friction, constant force must be
applied to maintain an object’s motion.
 Acceleration required unbalanced forces,
while constant velocity requires balanced
forces.
What is friction?
 Different
surfaces provide different
amounts of friction.
 For the purpose of machinery, you want
friction to be minimal.
 Air resistance is a form of friction that
results between the object falling and
the air molecules that surround it.
What are Newton’s three laws
of motion?
Newton’s First Law: An object at rest remains
at rest and an object in motion maintains its
velocity unless it experiences an unbalanced
force.
 Newton’s Second Law: The unbalanced
force action on an object equals the object’s
mass times its acceleration.
 Newton’s Third Law: For every action force,
there is an equal and opposite reaction force.

What are Newton’s three laws
of motion?
 You
may have heard these laws stated
in a more common way.
 1st: An object in motion tends to stay in
motion.
 2nd: Force equals mass times
acceleration.
 3rd: For every action, there is an equal
and opposite reaction.
What is efficiency?
 Efficiency
is the ratio of useful work
output to work input.
 It is generally expressed as a
percentage.
 The equation is efficiency = useful work
output  work input.
Efficiency Example Calculation

A sailor uses a rope and an old, squeaky
pulley to raise a sail that weighs 140 N. He
finds that he must do 180 J of work on the
rope in order to raise the sail by 1 m (doing
140 J of work on the sail). What is the
efficiency of the pulley?
 E = Wo / Wi
 E = 140 / 180
 E = 0.78
 0.78 (100 %) = 78%
What is mechanical
advantage?
 Mechanical
advantage is a quantity that
measures how much a machine
multiplies force or distance.
 Simple machines are designed to make
work easier.
 The equation is mechanical advantage
= output force  input force.
 There are no units.
How do I calculate mechanical
advantage?
 Calculate
the mechanical advantage of
a ramp that is 5.0 m long and 1.5 m
high.
 MA = Fo / Fi
 MA = 5.0 / 1.5
 MA = 3.3
How is force related to work?
 Work
is the energy transferred by a
force when it is applied to a body and
causes that body to move in the
direction of the force.
 The equation is work = force X distance.
 A force causes an object to move, in
order for work to be done.
How are work problems
solved?
 The
distance traveled by the object and
the force applied to the object are
determined.
 The values of force and distance are
substituted into the equation.
 The units for work are Joules.
Work Example Calculation
 Imagine
a father playing with his
daughter by lifting her repeatedly in the
air. How much work does he do with
each lift, assuming he lifts her 2.0 m
and exerts an average force of 190 N?
 W = fd
 W = 190 X 2.0
 W = 380 J
What is energy?
 Energy
is the ability to do work, so it is
very closely related to work.
 However, it can be present whether an
object is in motion or at rest.
 The units are Joules, just like for work.
 Energy can be potential or kinetic.
What is the law of
conservation of energy?

The law of conservation of energy states that
energy cannot be created or destroyed. It
can only change forms.
 Complicated calculations have been
completed to prove this law.
 The conservation of energy depends on
whether or not a system is open (energy
flowing in and out easily) or closed (energy
exchange with outside limited).
How do I calculate potential
and kinetic energy?
 Determine
which form of energy is
present by deciding whether the object
is in motion.
 Substitute given values into the correct
equations.
Potential Energy Example
Calculation
 A 65
kg rock climber ascends a cliff.
What is the climber’s gravitational
potential energy at a point 35 m above
the base of the cliff?
 PE = mgh
 PE = 65 X 9.8 X 35
 PE = 22000 J
Compare potential and kinetic
energy.

Potential



Stored energy of
object at rest
Equation: PE =
mass X gravity X
height
Depends on mass
and height

Kinetic



Energy of an object
in motion
Equation: KE = ½ X
mass X velocity
squared
Depends on mass
and speed
Kinetic Energy Example
Calculation
 What
is the kinetic energy of a 44 kg
cheetah running at 31 m/s?
 KE = ½ mv2
 KE = 0.5 X 45 X 312
 KE = 21000 J
What is thermal energy and how
is it related to temperature?
 Temperature
is the measure of the
average kinetic energy of the molecules
of an object.
 As molecules move and collide, they
give off energy in the form of heat.
 This heat is measured as temperature
change.
Describe the flow of energy
through matter.
 Energy
can be transmitted using
conduction, convection, or radiation.
 Particles within objects are in constant
motion, so they are constantly coming
into contact with other particles.
 Energy is transferred with or without
matter and in different phases of matter.
Compare the three forms of
energy transfer.
Convection
Conduction
Radiation
Objects in direct
contact
Movement of
warm fluids
Electromagnetic
waves
Objects at
unequal
temperatures
Unequal
densities
Infrared radiation,
visible light,
ultraviolet rays
Heating a wire
directly in a fire
Heat pump
Sun warming
Earth
How is work related to force
and energy?
 Energy
is the ability to do work, so it is
very closely related to work.
 When calculating total amounts, work is
equal to energy.
 The equations for the two can be
interchanged.
 Force is what causes work and energy.
What is power?
 Power
measures the rate at which work
is done.
 The equation is power = work ÷ time.
 The unit for power is watts.
 Power can change if the work done or
the time needed to do the work
changes.
How are work and power
related?
 The
length of time it takes to do work is
expressed in power.
 Greater work requires greater power.
 Speeding up or slowing down changes
the amount of power used.
P = W / t
Work Example Calculation
 It
takes 100,000 J of work to lift an
elevator 18 m. If this is done is 20 s,
what is the average power of the
elevator during the process?
P = W / t
 P = 100000/ 20
 P = 5000 watts
What are electromagnetic
forces?
 Electromagnetic
forces involve the
properties of electricity and magnetism.
 An electromagnet is a strong magnet
created when an iron core is inserted
into the center of a current-carrying
solenoid.
Explain the relationship between
electricity and magnetism.
 With
electricity, the exchange of
electrons creates a force between
objects.
 Electric currents produce magnetic
fields.
 The flow of electrons creates a north
and south pole.
What is the difference between
induction and conduction?

Induction is the production of a current by
changing the strength, position, or orientation
of an external magnetic field.
 Conduction is the transfer of energy as heat
between particles as they collide within a
substance or between two objects in contact.
 Conduction requires objects to be in contact.
Induction does not.
What is Ohm’s Law?
Ohm’s law says that in an electrical circuit,
current is directly proportional to the potential
difference (voltage drop) and inversely
proportional to the resistance.
 This means that when current is increased,
voltage increases and resistance decreases.
 Resistance = voltage  current

Resistance Example Calculation
 The
headlights of a typical car are
powered by a 12 V battery. What is the
resistance of the headlights if they draw
3.0 A of current when turned on?
R = V / I
 R = 12 / 3
 R = 4 Ohms
How do electrical circuits
work?
 An
electrical circuit is a device
connected so that it provides one or
more complete paths for the movement
of charges.
 Electrons move from the power source
through the wires to power a bulb and
move on to return to the power source.
An Electrical Circuit
Identify methods for creating electrical charge with
mechanical, magnetic, and chemical methods.
Mechanical
Magnetic
Chemical
Charge
created by
motion
Charge
created by
changing
magnetic field
Charge
created by
breaking of
bonds
How is energy transferred by
mechanical waves?

Waves can do work because they carry
energy.
 The particles move up and down, but they
never leave their horizontal positions.
 Think of people doing the wave in a stadium.
They stand up and sit down, but they do not
leave the location of their seats.
 As the energy moves forward, the next
molecules are lifted and set back down. The
particles do not actually leave their original
locations.
Compare transverse and
longitudinal waves.

Transverse


Motion of particles
perpendicular to
motion of entire
wave
Light waves

Longitudinal


Motion of particles
parallel to motion of
entire wave
Sound waves
How is energy transferred by
electromagnetic waves?

A charged particle moving in a magnetic field
will experience a force due to the magnetic
field.
 The force causes energy to move forward.
 Electromagnetic waves are transverse, so
particles move up and down as energy
passes. They do not move horizontally.
What are the physical
properties of waves?

The top of a wave is called the crest, and the
bottom is the trough.
 The measurement from crest to crest or
trough to trough is the wavelength.
 The distance the particles in a medium move
when a wave passes is the amplitude.
 The length of time necessary for a wave to
pass is the period, and the number of waves
to pass in a given time is the frequency.
Wave Properties
How do the properties of
waves create sound and light?

Light waves are transverse, and sound waves
are longitudinal.
 Light acts as a wave and as a particle. The
particles of light move in the manner of a
wave to create luminescence. They travel in
straight lines.
 Sound waves are caused by vibrations. They
move out in all directions from the source.
The waves cause the eardrum to vibrate.
What are nuclear forces?
 Nuclear
forces are short-range
attractions between neutrons and
protons within the nuclei of atoms that
cause atoms to be held together.
 They are caused by the mass of the
nuclear particles.
The Nucleus
What is the structure of an
unstable isotope?

An unstable nucleus is called a radioactive nuclide,
and it is capable of undergoing radioactive decay.
 This process is spontaneous, meaning it happens
without warning.
 The nucleus disintegrates into a slightly lighter
nucleus and emits particles, electromagnetic
radiation, or both.
 All elements with an atomic number higher than 83
are radioactive.
 The nucleus itself has a number of protons and
neutrons that causes it to be unstable.
Comparison of Nuclei
Compare the three types of
nuclear radiation.
Alpha
Beta
Gamma
Two protons and two
neutrons bound
together (helium
nuclei)
Electron
High energy
electromagnetic
waves
Stopped by paper
Stopped by lead
Stopped by concrete
Only very heavy
nuclei
Atomic number
increased by 1
Immediately after
other types of decay,
while nucleus is still
excited
Compare fission and fusion.

Fission



Nucleus splits into
two smaller nuclei
Tremendous amount
of energy released
Used in power plants

Fusion



Nuclei of two smaller
atoms join together
to make larger
nucleus
Requires extremely
high temperature
Energy of sun and
stars
What are the uses of nuclear
technology?
 Nuclear
power
 Medical tagging within body
 X-rays
 Radiation therapy
What are some possible side
effects of nuclear technology?
 Cancer
 Mutation
 Radiation
sickness