Physics Chapter 11 Energy & Energy Conservation

Objectives 11.1 Energy and Its Forms Define Potential and Kinetic Energy Calculate Kinetic Energy of an Object Apply the Work-Theorem to determine work done for an given change in KE Solve problems involving gravitational potential energy

5.1 The Nature of Energy Energy – the ability to do work or cause a change. Energy – the ability to do work or cause a change. work is the transfer of energy work is the transfer of energy SI unit for energy is the same as the SI unit for work – Joule SI unit for energy is the same as the SI unit for work – Joule Two main types of energy: Kinetic and Potential Two main types of energy: Kinetic and Potential Kinetic Energy: the energy of motion Kinetic Energy: the energy of motion Potential Energy: Energy stored for use at a later time Potential Energy: Energy stored for use at a later time

Different Forms of Energy 7 different forms : 7 different forms : Mechanical Mechanical Sound Energy Sound Energy Thermal Energy Thermal Energy Chemical Energy Chemical Energy Electrical Energy Electrical Energy Electromagnetic Energy Electromagnetic Energy Nuclear Energy Nuclear Energy

5 Science STAAR Need to Know Kinetic Energy (KE) Energy due to motion of an object Speed & mass affect kinetic energy– Faster/heavier…more Kinetic Energy Did you know that the gas burned in a car engine is chemical energy being turned into Kinetic Energy? Rubber band flying through the air has kinetic energy

The work-energy theorem states that whenever work is done, energy changes. 9.6 Work-Energy Theorem W net =ΔKE

7 Science STAAR Need to Know

Calculating Kinetic Energy Kinetic Energy: the energy of motion Kinetic Energy: the energy of motion The amount of kinetic energy depends on the objects mass and velocity The amount of kinetic energy depends on the objects mass and velocity Energy is transferred during work Energy is transferred during work The more work one does on an object… The more work one does on an object… The more energy one imparts on the object The more energy one imparts on the object Kinetic energy = Mass x Velocity 2 Kinetic energy = Mass x Velocity 2 2 When mass is doubled; Kinetic Energy is doubled When velocity is doubled; Kinetic Energy is quadrupled!!

What’s the Kinetic Energy? What is the Kinetic Energy (in Joules) of an object with a mass of 10 kg and a velocity of 10 m/s? What is the Kinetic Energy (in Joules) of an object with a mass of 10 kg and a velocity of 10 m/s? When mass is doubled; Kinetic Energy is doubled When mass is doubled; Kinetic Energy is doubled When velocity is doubled; Kinetic Energy is quadrupled!! When velocity is doubled; Kinetic Energy is quadrupled!!

10 Science STAAR Need to Know Potential (PE) Stored energy

Three examples of potential energy are elastic potential energy, chemical energy, and gravitational potential energy. 9.4 Potential Energy

An object may store energy by virtue of its position. Energy that is stored and held in readiness is called potential energy (PE) because in the stored state it has the potential for doing work. Potential Energy

Elastic Potential Energy A stretched or compressed spring has a potential for doing work. When a bow is drawn back, energy is stored in the bow. The bow can do work on the arrow. A stretched rubber band has potential energy because of its position. These types of potential energy are elastic potential energy. Potential Energy

Chemical Energy The chemical energy in fuels is also potential energy. It is energy of position at the submicroscopic level. This energy is available when the positions of electric charges within and between molecules are altered and a chemical change takes place. Potential Energy

Gravitational Potential Energy Work is required to elevate objects against Earth’s gravity. The potential energy due to elevated positions is gravitational potential energy. Water in an elevated reservoir and the raised ram of a pile driver have gravitational potential energy. Potential Energy

The amount of gravitational potential energy possessed by an elevated object is equal to the work done against gravity to lift it. The upward force required while moving at constant velocity is equal to the weight, mg, of the object, so the work done in lifting it through a height h is the product mgh. gravitational potential energy = weight × height PE = mgh Potential Energy

Potential Energy: Energy stored for use at a later time Energy stored for use at a later time Gravitational Potential Energy: Gravitational Potential Energy: Height and weight dependant (notice its weight, NOT mass!) Height and weight dependant (notice its weight, NOT mass!) GPE = work done to lift and object to a height GPE = work done to lift and object to a height GPE = Weight x Height (remember that weight = mass x 9.8 m/s 2 ) GPE = Weight x Height (remember that weight = mass x 9.8 m/s 2 ) GPE = mass x 9.8 m/s 2 x Height GPE = mass x 9.8 m/s 2 x Height GPE = 100 N x 300 m = 30,000 Nm = 30,000 Joules

The potential energy of the 100-N boulder with respect to the ground below is 200 J in each case. A. The boulder is lifted with 100 N of force. B. The boulder is pushed up the 4-m incline with 50 N of force. C. The boulder is lifted with 100 N of force up each 0.5-m stair. Potential Energy

Homework Read Pages Practice Problems: 2 & 3 page – 7 page 224

Objectives: State the law of conservation of energy Solve problems using the concept of conservation of energy Determine the quantities conserved in elastic and inelastic collisions 11.2 Conservation of Energy

More important than knowing what energy is, is understanding how it behaves—how it transforms. We can understand nearly every process that occurs in nature if we analyze it in terms of a transformation of energy from one form to another. Conservation of Energy

Mechanical Energy Associated w/ the motion (kinetic) and position of an object (potential) Associated w/ the motion (kinetic) and position of an object (potential) Kinetic Energy exists whenever an object which has mass is in motion with some velocity. Everything you see moving about has kinetic energy. Kinetic Energy exists whenever an object which has mass is in motion with some velocity. Everything you see moving about has kinetic energy. Potential Energy exists whenever an object which has mass has a position within a force field. (Gravity, Electric, Magnetic, Elastic) Potential Energy exists whenever an object which has mass has a position within a force field. (Gravity, Electric, Magnetic, Elastic) Mechanical Energy = Potential Energy + Kinetic Energy Mechanical Energy = Potential Energy + Kinetic Energy GPE = Weight x Height

The study of the forms of energy and the transformations from one form into another is the law of conservation of energy. For any system in its entirety—as simple as a swinging pendulum or as complex as an exploding galaxy—there is one quantity that does not change: energy. Energy may change form, but the total energy stays the same. Conservation of Energy

Part of the PE of the wound spring changes into KE. The remaining PE goes into heating the machinery and the surroundings due to friction. No energy is lost. Conservation of Energy

Everywhere along the path of the pendulum bob, the sum of PE and KE is the same. Because of the work done against friction, this energy will eventually be transformed into heat. Conservation of Energy

When the woman leaps from the burning building, the sum of her PE and KE remains constant at each successive position all the way down to the ground. Conservation of Energy

HW Problems Read Pages 227 to 230 Do practice problems: 9-11 pg 230

Sound Sound Copyright © 2010 Ryan P. Murphy

Sound Energy: Caused by an object's vibrations. Sound energy is both kinetic and potential energy. Copyright © 2010 Ryan P. Murphy

Activity Simulator: Soundwaves

Thermal Energy associated w/ the total energy of the particles (atoms and molecules) in an object. As thermal energy increases, the particles increase in speed and the thermal energy (temperature) of the object increases. associated w/ the total energy of the particles (atoms and molecules) in an object. As thermal energy increases, the particles increase in speed and the thermal energy (temperature) of the object increases.

Chemical Energy the energy stored in chemical bonds. The potential energy stored in compounds. the energy stored in chemical bonds. The potential energy stored in compounds.

Electrical Energy Moving electrical charges. Electricity!! Moving electrical charges. Electricity!!

Electromagnetic energy Travels in waves, associated w/ light, infrared, ultraviolet, microwaves, x-rays, etc Travels in waves, associated w/ light, infrared, ultraviolet, microwaves, x-rays, etc Longer wavelength yields low frequency & low energy Longer wavelength yields low frequency & low energy Shorter wavelength yield high frequency & high energy Shorter wavelength yield high frequency & high energy

Nuclear Energy Associated w/ the fusion or fission of nuclear atoms. Associated w/ the fusion or fission of nuclear atoms. The fusion of hydrogen into helium fuels the power of the sun

36 Science STAAR Need to Know Energy Transformations Potential energy A rock sitting at the top of a cliff Roller coaster car at the top peak of a hill A swimmer posed to dive off the end of a diving board NO MOTION !! Kinetic energy A bouncing ball A moving roller coaster A track star running A girl skiing MOTION is the key!!!!

5.2 Energy Conversion and Conservation Most forms of energy can be converted from one type to another. Mechanical Energy = PE + KE Most forms of energy can be converted from one type to another. Mechanical Energy = PE + KE Law of the Conservation of Energy - states that energy cannot be created or destroyed. It simply changes from one form into another Law of the Conservation of Energy - states that energy cannot be created or destroyed. It simply changes from one form into another Einstein’s theory of Relativity - E = mc 2 Einstein’s theory of Relativity - E = mc 2 a small amount of mass can be changed directly into a tremendous amount of energy a small amount of mass can be changed directly into a tremendous amount of energy E = the energy produced E = the energy produced m = the mass being converted m = the mass being converted c = the speed of light (186,000 miles/second) c = the speed of light (186,000 miles/second)

Energy Conversion