ENERGY Sabar Nurohman,M.Pd

Energy as a tool in physics The Flow of Energy 4/11/2005 Energy is a very abstract notion, but it is a very useful and quantifiable notion We use the conservation of energy to predict behavior by setting E = mgh + ½mv2 = constant we can elucidate the value of the velocity at any height: v2 = 2g(height fallen from rest) We rely on the fact that energy is not created out of nowhere Where did the energy we see around us come from? most of what we use derives from the sun some derives from other, exploded stars (nuclear fission) ultimately, all of it was donated in the Big Bang but surprisingly, the net energy of the universe can be (and looks to be) zero! Lecture 4

Energy is Conserved The Flow of Energy 4/11/2005 Conservation of Energy is different from Energy Conservation, the latter being about using energy wisely Conservation of Energy means energy is neither created nor destroyed. The total amount of energy in the Universe is constant!! Don’t we create energy at a power plant? No, we simply transform energy at our power plants Doesn’t the sun create energy? Nope—it exchanges mass for energy Lecture 4

The Flow of Energy Energy Exchange 4/11/2005 Though the total energy of a system is constant, the form of the energy can change A simple example is that of a pendulum, in which a continual exchange goes on between kinetic and potential energy pivot K.E. = 0; P. E. = mgh K.E. = 0; P. E. = mgh height reference h P.E. = 0; K.E. = mgh Lecture 4

Perpetual Motion Why won’t the pendulum swing forever? The Flow of Energy 4/11/2005 Why won’t the pendulum swing forever? It’s impossible to design a system free of energy paths The pendulum slows down by several mechanisms Friction at the contact point: requires force to oppose; force acts through distance  work is done Air resistance: must push through air with a force (through a distance)  work is done Gets some air swirling: puts kinetic energy into air (not really fair to separate these last two) Perpetual motion means no loss of energy Lecture 4

Mechanical, Electromagnetic, Electrical, TYPES OF ENERGY Mechanical, Electromagnetic, Electrical, Chemical and Thermal

What is Mechanical Energy? Energy due to a object’s motion (kinetic) or position (potential). The bowling ball has mechanical energy. When the ball strikes the pins, mechanical energy is transferred to the pins!

Examples of Mechanical Energy

What is Electromagnetic Energy? Light energy Includes energy from gamma rays, xrays, ultraviolet rays, visible light, infrared rays, microwave and radio bands

What is Electrical Energy? Energy caused by the movement of electrons Easily transported through power lines and converted into other forms of energy

What is Chemical Energy? Energy that is available for release from chemical reactions. The chemical bonds in a matchstick store energy that is transformed into thermal energy when the match is struck.

Examples of Chemical Energy

What is Thermal Energy? Heat energy The heat energy of an object determines how active its atoms are. A hot object is one whose atoms and molecules are excited and show rapid movement. A cooler object's molecules and atoms will show less movement.

ELECTROMAGNETIC ENERGY QUIZ TIME! What type of energy cooks food in a microwave oven? ELECTROMAGNETIC ENERGY What type of energy is the spinning plate inside of a microwave oven? MECHANICAL ENERGY

QUIZ TIME! Electrical energy is transported to your house through power lines. When you plug an electric fan to a power outlet, electrical energy is transform into what type of energy? MECHANICAL ENERGY

QUIZ TIME! What energy transformation occurs when an electric lamp is turned on? ELECTRICAL ENERGY  ELECTROMAGNETIC ENERGY

What types of energy are shown below? Mechanical and Thermal Energy (Don’t forget friction)

What type of energy is shown below? Chemical Energy

What types of energy are shown below? Electrical, Mechanical and Electromagnetic Energy

What type of energy is shown below? Chemical Energy (yummy)

What type of energy is shown below? Thermal Energy

Draw a flow map showing the flow of energy transformations in a car from starting vehicle to driving. You should have 5 different types of energy.

Energy Transfer Sound (mechanical) Electrical Thermal Mechanical Chemical Electrical Light (Electromagnetic)