Chapter 15: Energy Section 15.1 Energy and Its Forms Section 15.2 Energy Conversion and Conservation Section 15.3 Energy Resources

Section 15.1 Energy and Its Forms Energy and Work Work is done when a force moves an object through a distance. Energy-the ability to do work Ie. Energy is transferred by a force moving an object through a distance. When work is done on an object, energy is transferred to that object.

Section 15.1 Energy and Its Forms Energy and Work Key Concept: Work is a transfer of energy. Measured in joules (J)=1 newton-meter Energy has different forms and comes from different sources: sunlight, food, etc.

Section 15.1 Energy and Its Forms Kinetic Energy Many forms of energy can be classified into two general types: kinetic and potential energy. Kinetic energy-the energy of motion Key Concept: The kinetic energy of any moving object depends upon its mass and speed.

Section 15.1 Energy and Its Forms Kinetic Energy Kinetic energy (KE)=1/2mv2 -m=mass (kg); v=speed (m/s) **doubling the mass will double the kinetic energy; doubling the speed will quadruple it

Section 15.1

Section 15.1 Energy and Its Forms Potential Energy def.-energy that is stored as a result of position or shape Is converted to kinetic energy Two types: gravitational potential energy and elastic potential energy Gravitational-potential energy that depends upon an object’s height

Section 15.1 Energy and Its Forms Potential Energy Key Concept: An object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity. Potential energy (PE)=mgh; m=mass, g=acceleration due to gravity, h=height Gravitational potential energy is directly related to the mass of the object and its height .

Section 15.1 Energy and Its Forms Potential Energy Elastic potential energy-the potential energy of an object that is stretched or compressed “elastic”-something springs back to its original shape after being stretched or compressed. Ex. Rubber bands, springs

Section 15.1 Energy and Its Forms Forms of Energy Key Concept: The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy, and nuclear energy. Each form can be converted into other forms of energy.

Section 15.1 Energy and Its Forms Forms of Energy mechanical energy -the energy associated with the motion and position of everyday objects -mechanical energy does not include thermal energy, chemical energy, or other forms of energy

Section 15.1 Energy and Its Forms Forms of Energy thermal energy -the total potential and kinetic energy of all the microscopic particles in an object. As an object’s atoms move faster, its thermal energy increases and the object becomes warmer. Objects that are hot enough can emit light.

Section 15.1 Energy and Its Forms Forms of Energy chemical energy -the energy stored in chemical bonds. When bonds are broken, the released energy can do work. All chemical compounds store energy (including fuels).

Section 15.1 Energy and Its Forms Forms of Energy electrical energy -the energy associated with electrical charges They can exert forces that do work electromagnetic energy -a form of energy that travels through space in the form of waves (visible light, x-rays) Electromagnetic waves are often used for communication b/c they travel long distances.

Section 15.2 Energy Conversion and Conservation Key Concept: Energy can be converted from one form to another. def.-the process of changing energy from one form to another

Section 15.2 Energy Conversion and Conservation Conservation of Energy When energy changes from one form to another, the total energy remains unchanged even though many energy conversions may occur. Key concept: The law of conservation of energy states that energy cannot be created or destroyed.

Section 15.2 Energy Conversion and Conservation Energy Conversions **One of the most common energy conversions is between potential energy and kinetic energy. Key Concept: The gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls. Conversions b/t kinetic and potential energy can happen in both directions.

Section 15.2 Energy Conversion and Conservation Energy Conversion in Pendulums (A weight swinging back and forth from a rope or string) Ex. clocks Kinetic energy and potential energy undergo constant conversion as a pendulum swings. At highest point, pendulum is briefly motionless while it changes direction. The weight of the pendulum at that point has zero kinetic energy and maximum potential energy.

Section 15.2 Energy Conversion and Conservation Energy Conversion in Pendulums Pendulum swings down; potential energy is converted to kinetic energy Pendulum has maximum kinetic energy and zero potential energy as it reaches the bottom of the swing. (process repeats)

Energy Conversion in the Pole Vault Refer to Section 15.2 pg. 457

Section 15.2 Energy Conversion and Conservation Energy Conversion Calculations When friction is small enough to be ignored, and no mechanical energy is added to a system, the system’s mechanical energy does not change. ME= KE + PE Conservation of Mechanical Energy (KE+ PE) beginning = (KE + PE)end pg. 459

Section 15.2

Section 15.2 Energy Conversion and Conservation Energy and Mass Einstein-developed his theory of relativity in 1905 Key Concept: Einstein’s equation, E=mc2, says that energy and mass are equivalent and can be converted into each other. E=energy; m=mass; c=speed of light Energy is released as matter is destroyed, and matter can be created from energy. However, if was found that mass and energy together are always conserved (law of conservation of energy)

Section 15.3 Energy Resources Nonrenewable Resources **Energy resources can be classified as either renewable or nonrenewable Nonrenewable resources exist in limited quantities. Once used, can’t be replaced except over the course of millions of years. Key Concept: Nonrenewable energy resources include oil, natural gas, and uranium.

Section 15.3 Energy Resources Nonrenewable Energy Resources Ie. These resources are being used up much faster than they can be replaced. fossil fuels -rich deposits of hydrocarbons formed underground from the remains of once-living organisms (oil, natural gas, coal, and uranium) Majority of the world’s energy use comes from fossil fuels.

Section 15.3 Energy Resources Renewable Energy Resources -def.-resources that can be replaced in a relatively short period of time Most originate either directly or indirectly from the sun. (generating electric power) Key Concept: Renewable energy resources include hydroelectric, solar, geothermal, wind, biomass, and, possibly in the future, nuclear fusion.

Section 15.3 Energy Resources Renewable Energy Resources Hydroelectric Energy -energy obtained from flowing water Flowing water is used to turn turbines that are connected to electric generators. Advantage: low cost, lack of pollution Disadvantage: dams cause environmental problems (fish population)

Section 15.3 Energy Resources Renewable Energy Resources Solar Energy -sunlight that is converted into unstable energy Used to warm houses, buildings, etc. (Heats water) Sunlight can be converted to electrical energy (calculators) Adv. Nonpolluting; Dis. Cloudy areas

Section 15.3 Energy Resources Renewable Energy Resources Geothermal Energy -thermal energy beneath Earth’s surface. Areas near volcanoes: this energy is used to generate electricity. Water can be pumped into the ground and be turned into steam. Nonpolluting but not widely available

Section 15.3 Energy Resources Other Renewable Resources Biomass energy-the chemical energy stored in living things (can be converted directly into thermal energy) Ex. Using wood or peat to heat homes or cook; corn stalks used for high-energy alcohol fuel

Section 15.3 Energy Resources Other Renewable Resources Hydrogen fuel cells-generate electricity by reacting hydrogen with oxygen (can be used to convert energy from renewable resources) Ex. Hydrogen fuel End product is water so: nonpolluting means for transporting energy A form of hydrogen is also most likely raw material for nuclear fusion (future). In physics and nuclear chemistry, nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy.

Section 15.3 Energy Resources Conserving Energy Resources Key Concept: Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy use. energy conservation -finding ways to use less energy or to use energy more efficiently People should make energy-saving decisions to reduce the use of resources.