Download Final Exam Book Notes

Final Exam Book Notes
Written By Chris Ragsdale
2-3 Motion and Force: Summary
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What is a Force?
 Force - a push or pull that on body exerts on another
 There are obvious and unnoticeable forces
 Force can cause the motion of an object to change
 Net Force - when two or forces act on an object at the same time
 Balance Forces - forces on an object that are equal in size and opposite
in direction
 Unbalanced forces - when two forces are pushing with unequal forces
in the opposite direction
Inertia and Mass
 Inertia - the tendency of an object to resist any change in its motion
 Velocity of object is constant unless a force acts on it
 The greater the mass of an object, the great its inertia
 1st Law of Motion - any object moving at a constant velocity keeps
moving at that velocity unless a net force acts on it; if an object is at
rest it will remain at rest unless a net force acts on it
What Happens First?
 A car stops within 0.01 seconds
 People in car keep traveling at the same speed and slam into something
with 0.02 seconds
3-1 Newton’s Second Law
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Force, Mass, and Acceleration
 Second law states that motion of an object changes only if unbalanced
force acts on it
 The greater the force, the greater the acceleration
 Acceleration of object depends on its mass and the force exerted on it
Newton’s Second Law
 According to second law, net force acting on object causes an object to
accelerate in the direction of the net force
Friction
 The force that opposes motion between two surfaces that are touching
each other
 Amount of friction depends on the finds of surfaces and the forces
pressing the surfaces together
 The source of friction are microwelds which are where highest bumps
on the surfaces come together and stick or weld
 The stronger the force pushing the surfaces together, the stronger the
microwelds
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Static friction is the friction between two surfaces that are not moving
past each other
 Sliding friction is the force that opposes the motion of two surfaces
sliding past each other
 Sliding friction is caused by microwelds breaking and then sticking
over and over again.
 Rolling friction is the friction between a rolling object and the surface it
rolls on
Air Resistance
 Acts in the opposite direction of gravity
 Depends on speed, size, and shape of the object
 Terminal velocity is the highest velocity that a falling object will reach
3-3 The Third Law of Motion
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Newton’s Third Law
 Describes action-reaction pairs: when one object exerts a force on
another object, the second exerts a force on the first that is equal is size
and opposite in direction
 To every action force there is an equal in opposite reaction force
 Though force may be equal, they may not balanced because they act on
different objects allowing a swimmer to swim in water, etc.
 Burning fuel in a rocket produces hot gases and the engine exerts a
force on the gases and causes them to escape, then the gases exert a
force on the rocket and propel in forward
4-1 The Nature of Energy
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What is Energy?
 Every change involves energy
 Energy is the ability to cause change
 Different forms include electrical, chemical, and thermal
 Money Analogy
Kinetic Energy
 Energy in the form of motion
 The more mass or velocity that a moving object has, the more kinetic
energy it has
 Kinetic energy = ½ mass x velocity2
 KE (J) = ½ m (kg) x v2 (m2s2)
 Joule is SI unit of energy
Potential Energy
 Energy can be stored in an object and therefore it has the potential to
cause change
 Potential energy - Stored energy due to position
 Elastic potential energy - energy stored by something that can
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compress or stretch
Chemical potential energy - energy stored in chemcial bonds; some
examples are food and gas
Gravitational potential energy - energy stored by objects that are above
earth’s surface; anything that can fall has this
GPE = mass x 9.8 x height
GPE (J) = m (kg) x 9.8 m/s2 x h (m)
Changing GPE
4-2 Conservation of Energy
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Changing Forms of Energy
 Energy is most noticeable when it is changing forms
 A light bulb transforms electrical energy into thermal energy
 An engine transforms potential chemical energy in gasoline into kinetic
energy for the car
 Some transformations are less visible because they do not results in
visible light, sound, heat, or motion
Conversions between Kinetic and Potential Energy
 Mechanical energy - total amount of potential and kinetic energy in a
system
 Mechanical energy = PE + KE
 Mechanical energy is always constant when something is falling or
moving
 When you are higher your GPE is higher and your KE is lower
The Law of Conservation of Energy
 States that energy cannot be created or destroyed
 The total amount of energy in the universe is always constant
 You can change the form of energy but cant change the amount
 It is not always easy to see that the law of conservation of matter is at
work because a lot of energy goes to friction
 Of the mechanical energy of an object decreases, then then the energy
of another object MUST increase by an equal amount to keep the total
amount of energy the same
 Nuclear fusion takes place in the sun
 In this process a small amount of mass is transformed into a large
amount of energy
 Nuclear fission - converts a small amount of mass into large quantities
of energy; nuclei are broken apart
The Human Body - Balancing the Energy Equation
 Some potential energy in your body is used to maintain a constant
internal temperature and some is converted to excess heat that is given
off to your surroundings
 Body stores energy in form of fat and other chemical compunds
 This is used to fuel processes that keep you alive and some is used as
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body heat
 To maintain healthy weight you must have an equal amount of energy
you retain and that you use
 Your body breaks down your food into molecules that can be used as
fuels and if you don’t eat it will take it from stored fat
 One calorie = 4184 joules
 One calorie = 1/9 grams
 One calorie = ¼ carbs
Section Review
1. Mechanical energy is total amount of potential and kinetic energy in a
system. A roller coaster’s mechanical energy when it is just about travel
downwards, its mostly and gravitational potential energy and very little
kinetic energy.
2. The Law of Conservation of Energy states that energy cannot be
created or destroyed.
3. When the bicycle brakes, its mechanical, or kinetic, energy is lost and
it is transferred into the biclyle’s brakes
4. The source of large amounts of energy that are released in nuclear
reactors in the sun is the mass of nuclei. With the sun, nuclear fusion
takes place where nuclei are fused together. With nuclear reactors,
nuclear fission takes place where nuclei are broken apart.
Chapter 5, Section 1
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What is work?
 Transfer of energy that occurs when a force makes an object move
 Scientific meaning of work is more specific
 Two conditions for work to be done on an object: object has to move,
motion of the object must be in the same direction as the applied force
Work and energy
 When work is done a transfer of energy always occurs
 Energy is the ability to do work
 When you do work on an object you increase its energy
 Work is equal to force times distance
 W=Fxd
 Work is measured in joules
 Force is measured in Newtons
Power
 Amount of work done in a certain amount of time
 Power is a rate
 Rate at which work is done
 Power is equal to work divided by time
 P = W/t
 Power is measured in Watts and horsepower
 1kW is equal to 1000 Watts
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Doing work is a way of transferring energy from one object to another
Power is produced or uses any time energy is transferred from one
object to another
 Power is equal to energy divided by time
 P = E/t
Chapter 10, Section 2
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Using Nuclear Energy
 Energy is released when the nucleus of an atom breaks apart
 20% of the electricity in the USA comes from nuclear power plants
Nuclear reactors
 Uses energy from control nuclear reactions to generate electricity
 Contains fuel used to undergo nuclear fission, a control Rod, a cooling
system, and a core
 Fuel Comes in tiny pellets
 Nuclear chain reactions can occur where one split apart causes and
other to to split apart
 Control rods absorb neutrons to prevent chain reactions
the risks of nuclear power
 Do not produce pollutants or carbon dioxide
 Water used as coolant must cool before entering body of water
 Harmful radiation could escape from nuclear power plants
 However there are safeguards
The disposal of nuclear waste
 The nuclear waste is any radioactive byproduct that results when
radioactive materials are used
 Most have short half lives
 Low level waste is sealed in containers and buried in trenches and is
sometimes released if dilute enough
 High level waste is generated by nuclear power plants and nuclear
weapons programs
 High level waste is stored in a deep pool water
Nuclear fusion
 Thermonuclear Fusion is the joining together a small nuclei at high
temperatures
 Most concentrated energy source know
 Small amount of mass converted into energy
 Fuel used is hydrogen which is the most abundant
 No radioactive byproducts
 Must be at high temperatures
Chapter 10, Section 3
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Energy options
 A renewable resource is an energy source that is replaced nearly as
quickly as it is used
Energy from Sun
 In the sun is a renewable resource because the amount of solar energy
that falls on the USA in one day is more than what the USA uses in one
year
 The sun will be here for billions more years
Solar Cells
 Solar energy can be converted into electricity
 a photovoltaic cell is also called a solar cell and is used to convert
energy into electricity
 Solar cells are seven to 11% efficient
 Solar cells have two levels of semiconductors in between two layers of
conducting metal
 One semiconductor has many electronics and the other has none
 Using solar energy is very expensive
 At a disadvantage to solar energy the sun does not shy and 24/7 cell
batteries must be bought and used
Energy from water
 Energy carried by moving water can be retained by a dam
 This potential energy is released when the water goes through tunnels
 Hydroelectricity is electricity produced from the energy of moving
water
 This provides 8% of the energy used in the USA
 No pollution
 Dams can also create useful lakes
 dams can disturb the balance of natural ecosystems
Energy from the tides
 Hydroelectric power can be generated by tides
 As tide comes in the water Spins turbines
 Pollution free
 This can only work on a few places on earth
Harnessing the wind
 Windmills use energy of wind to pump water in generate electricity
 And only a few places on earth have enough wind for this
 20% efficient
 No pollution
 Noisy and disturb landscapes and migration
Energy from inside earth
 Heat in the earth is called geothermal heat
 Geothermal energy is thermal energy that is contained in hot magma
 In some places that are hot magma or hot water is able to seep through
the surface
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 Geothermal power plants are 16% efficient
Alternative fuels
 The use of fossil fuels would be reduced if cars can run on other fuels or
sources of energy
 Biomass is renewable organic matter like wood and animal manure
and can be used to heat water and produce electricity
Chapter 10, Section 1
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Using Energy
 To use energy mean to transform energy from to another form that can
perform a useful function
 USA uses mist energy
 85% of energy come from petroleum, natural gas, and coal
 8% of energy comes from nuclear energy
Making Fossil Fuels
 Takes millions of years to produce fuels used for energy
 Fossil fuels formed from the decay of dead plants and animals
 When fossil fuels burn the carbon and hydrogen combine with oxygen
to form carbon dioxide and water
 Energy in fossil fuels is very concentrated
Petroleum
 Highly flammable
 Pumped from wells deep within earth’s crust
 Made of many chemical compounds most of which are hydrocarbons
 Composition and structure of hydrocarbons determines properties
 Compounds are separated using fractional distillation
 Not all products in petroleum are burned to produce energy
Natural Gas
 Chemical processes that produce petroleum also produce natural gas
 Source of ¼ of energy in USA
 More concentrated than petroleum
 Less pollutants
Coal
 Solid found in mines
 Coal mines were once site of ancient swamps
 Hydrocarbons and other chemical compounds
 More pollutants
Efficiency of Power Plants
 35% efficiency
 65% of energy is lost when chemical energy in fuel is transformed into
electrical energy
The Cost of Using Fossil Fuels
 Gives off smoke that makes it harder to breather
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 Releases carbon dioxide causing global warming
 Most abundant fossil fuel is coal but it contains the most pollutants
Nonrenewable Sources
 All fossil fuels
 Cannot be replaced by natural processes as quickly as they are used
Workbook Chapter 26: Force Exerted by Fluids
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Density
 Fluids - liquids and gasses
 Density - mass of substance per unit volume
 Density = mass/volume
 Measured in grams per cubic centimeter or pounds per cubic foot
 Fluids with greater density exert more force
Pressure
 Amount of force exerted by a substance on a given unit of the area
 Pressure = force/area
 In English system, measured in: Pounds per square foot or pounds Per
square inch
 In metric system, measured in: grams per square centimeter or
Newtons for square meter
Pressure of Liquids
 Pressure of liquids depends on two factors: height and density
 Pressure of Liquid = Height x density
Characteristics of liquid pressure
 Pressure exerted by liquid acts equally in all directions and is
dependent on depth
 Liquids seek their own level
 The pressure of a liquid is independent of the shape of its container
 Pressure can be transferred throughout a liquid
 Pascal’s Law - in a closed container filled with a liquid, any additional
pressure applied to the liquid is transmitted without loss to all other
parts of the liquid
Pressure of Gasses
 Air pressure decreases as the altitude increases
 Air exerts pressure equally in all directions
 An increase in pressure reduces the volume of gases
 Boyle’s Law - volume of the gas varies inversely as the pressure on it
Measuring air pressure
 Barometer - instrument that measures air pressure
 Mercury barometer and aneroid barometer
 Mercury barometer was constructed by Torricelli
 Consists of 32in. Glass tubing that is closed at one end…glass tube is
first filled with mercury and then inverted into a dish of mercury…the
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mercury column falls but normally stops when its height reaches 30in.
(the maximum amount of mercury that the air pressing down on the
dish can support)…When the mercury in the tube moves down a partial
vacuum is created in the 2in. Of space above it… when air pressure
increases the mercury in the tube rises and vice versa
Air pressure in use
 Some devices such as a soda straw, medicine dropper, and vacuum
cleaner operate by reducing the air pressure inside them and allowing
outside air under its own pressure to put something into the device
Pressure Effects of Fluids at Rest
 For any object to lose weight the downward force exerted by gravity
must be opposed by an upward force
 Buoyant force - opposes the weight of an object and makes it appear to
lose weight
 Law of flotation - a floating objects displaces a weight of liquid equal to
its own weight
Specific gravity
 Ratio of the density of a substance to the density of water
 Determines whether or not an object will float
 Specific gravity = density of substance/density of water
 In specific gravity is less than one it will float