What is energy? Every change that occurs… big or small… requires energy. When something is able to change its environment or itself, it has energy. Energy is the ability to cause change.

Energy is an abstract idea that humans made up to explain their observations.

There are different types (or forms) of energy There are different types (or forms) of energy. Some examples are heat energy, light energy, electrical energy, and chemical energy.

Scientists believe that you cannot create energy from nothing, nor can you destroy energy so that none remains.

All that can happen to energy is that you can it from one place to another,

or you can from one form to another. This means that the total amount of energy in the universe stays the same.

Conservation of Energy Energy can neither be created nor destroyed; it can only change its form or location. This means that the total amount of energy always stays the same; i.e. it is conserved.

Sources of Usable Energy Renewable: wind, solar, biomass Nuclear: fission Hydroelectric: gravity and dams Fossil fuel: coal, oil The energy exists in these sources, but they must change form to be useful

Renewable: wind  electric

Renewable: solar  electrical

Renewable: Biomass

Nuclear Energy

Nuclear Energy: inside look

Nuclear Energy: inside look

Fossil Fuels: coal, oil, natural gas

Mechanical energies Total energy=KE+PE (total)=constant Energy stored by a change in configuration - Potential energy – e.g., gravity: PE=mgh Where do we measure this height from? From anywhere we want! Energy of Motion – KE = ½ mv2 Energy of Motion is independent of which way you are going! Total energy=KE+PE (total)=constant

Energy Conservation Like momentum, energy is a conserved quantity. This provides powerful constraints on what can and cannot happen in nature. This is an extremely important concept, and we will come back to this over and over throughout the remainder of the course.

Processes for Transferring Energy By doing work: macroscopic displacement By heat: random molecular collisions By conversion of energy forms: light to electrical; chemical to electrical, mechanical to electrical (generator), electrical to mechanical (motor) By chemical reaction: releasing energy to the system

Changing Forms of Energy Energy is most noticeable as it transforms from one type to another. What are some examples of transforming electrical energy? A lightbulb A hair dryer

Changing forms of Energy An example of transforming chemical energy is a car engine. Chemical potential energy in gasoline is transformed into kinetic energy of the car as it moves!!

Heat Energy Heat is the transfer of energy from other forms to the internal motion of molecules.

Temperature and Heat When heat is transferred into matter, the average kinetic energy of the atoms and molecule in that matter increases. Some of it also goes to elastic potential enegies among molecules: Internal Energy. Temperature is a measure of that average Internal Energy of molecules!

Insulators Insulators do not conduct heat easily. Examples are glass, wood, plastic, rubber and air. Materials that trap air, such as foam, fur and feathers, and double-paned windows are the best insulators.

Conduction

SI Unit of Thermal Conductivity: J/(s · m · C°) Conduction Rate of heat transfer by conduction, Q/t through the length, L across the cross-sectional area, A is given by the following equation, where k is the thermal conductivity and ΔT is the temperature difference between the two ends. When thermal conductivity is low, [air=0.023 J/(s · m · C°)], conduction is slow. Glass conductivity=0.8 J/(s · m · C°): double pane windows are effective due to the air gap. SI Unit of Thermal Conductivity: J/(s · m · C°)

Q: In the living room, the heating unit is placed in the floor but the the refrigerator has a top-mounted cooling coil. Why? A: Air warmed by the baseboard heating unit is pushed to the top of the room by the cooler and denser air. Air cooled by the cooling coil sinks to the bottom of the refrigerator.

Energy from Light Solar Cell Photo cell

Electrical Energy Electrical energy comes from various sources: Nuclear: fission (nuclear  heat  electrical) Hydroelectric: dams (mechanical  electrical) Chemical: batteries (electron flow) Solar: cells (solar  chemical  electrical Wind (mechanical  electrical) [generators] Fossil fuel (thermal  electrical)

Gravitational Potential Energy Gravitational potential energy (GPE) is stored by objects that are above the Earth’s surface. GPE depends on: The mass of the object The acceleration due to gravity The height above the ground Gravity converts PE of the water on top of a dam to KE; moving water turns a generator transferring mechanical energy to electrical energy

Circuits Electrical circuits consist of a power source (e.g., battery or generator) and circuit elements (lights, capacitors, motors, etc.) connected in closed loops Loops are typically series (all in a row) or parallel (connected together) or combinations thereof

Series circuits Single uninterrupted Loop of elements: same current (charge flow) goes through each element. Voltages (energy per charge) add. Potential is electric energy per charge: Voltage=potential

Parallel circuits Parallel circuits have elements connected on both sides of each. The same electrical potential is across each, while the currents split up. If one “leg” fails, the others Still function as a closed circuit.

Chemical Potential Energy Energy stored in chemical bonds is called chemical potential energy. Chemical energy is stored in bonds that hold a molecule together and are released when the bond is broken.

Energy in Your Body Even the energy converted in your body follows the law of conservation of energy. Chemical potential energy is transferred to kinetic energy that allows your body to move!!

Magnetism

Properties of Magnets Each magnet has two “poles” – North & South Like poles repel; different poles attract Magnets can be used to convert energy from one form to another. Examples: Magnets can move magnetic materials around Electromagnets can attract materials to be moved by other devices (e.g., crane in a junk yard) Magnets can levitate trains for easy movement Non-uniform magnetic fields can accelerate particles for high energy research

Summary of Energy Concepts Energy comes in different forms There are many sources of energy for use Energy is conserved: neither created or destroyed, merely changes forms Mechanisms that convert energy from one form to another have many practical applications Energy is a major part of our existence and an understanding of its nature is an important part of understanding our world!