Chapter 4: ENERGY

Section 1

The Nature of Energy

What is Energy?

• Energy is the ability to cause change.

• Every change that occurs requires energy.• https://www.youtube.com/watch?v=lmIFXIXQQ_E

Energy Has Different Forms• Some forms of energy

– Electrical

– Chemical

– Radiant

– Thermal

Forms of Energy

• Some things can have more than one type of energy at a time.

• Energy can convert from one form to another.

• Energy can be stored in

many ways.

Electrical Energy

• Electric circuit– http://www.rkm.com.au/animations/animation-

electrical-circuit.html

Chemical Energy

• Chemical change animation– http://www.tutorvista.com/content/chemistry/c

hemistry-i/physical-chemical-changes/physical-chemical-changes-animation.php

– How MRE heaters work• http://recipes.howstuffworks.com/mre4.htm

Radiant Energy

More Radiant Energy Examples

Thermal Energy

Other Forms of Energy. . .

• There are also these types of energy:– Kinetic energy is the energy of a moving

object.– Potential energy comes in 3 different forms:

• Gravitational potential is stored energy due to an object’s position.

• Elastic potential energy stored by something that can stretch, compress, or bend—like a rubber band, spring, or pole vault.

• Chemical potential energy is the energy stored in chemical bonds.

Kinetic Energy

Kinetic energy is measured in joules•Use the formula KE=1/2 mass x velocity2

•In other words: 1/2mv2

Gravitational Potential Energy

Watch out for falling rocks . . . and cows!http://www.tutorvista.com/content/physics/physics-i/work-energy-power/potential-energy-animation.php

Converting GPE to Kinetic Energy

• As an object falls, its potential energy is converted into kinetic (moving) energy.– As the object approaches the ground, it will have the

greatest kinetic energy—and the least potential energy.

• The gravitation potential energy (GPE) can be calculated using this formula:– Mass (kg) x acceleration due to gravity (m/s2) x height of object (m)– In other words:

kg x m/s2 x m = GPE

or mgh = GPE

Elastic Potential Energy

• Watch this: http://www.youtube.com/watch?v=u2-od4n5Xl0

• And these: http://www.youtube.com/watch?v=AjD0hXweqLM

• http://www.youtube.com/watch?v=IIy80bFS2IY• http://www.youtube.com/watch?v=8_RfK2rp2To• http://www.youtube.com/watch?v=msyii5E3lNg

Chemical Potential Energy

• Watch this:

http://www.youtube.com/watch?v=MMB2VR0087w

• And this: http://www.youtube.com/watch?v=fB33NsuFbV0&feature=list_related&playnext=1&list=PLA46E338EFA196C4E

Section 2: Conservation of Energy

Electrical Energy

• Electrical energy can be transformed into – Thermal energy– Radiant energy– Mechanical energy– Sound Energy

Chemical Energy Transformed into

– Radiant energy– Sound– GPE– Kinetic/mechanical

energy– Thermal energy– Car Engine Animation

• http://www.youtube.com/watch?v=QXLsna21FWo

• http://auto.howstuffworks.com/engine1.htm

Kinetic to Potential Energy

• Pendulum swinging is a good example.

More Potential to Kinetic• Mechanical energy is the

total amount of potential and kinetic energy in a system.– Formula:

ME = PE + KE• What happens to the

mechanical energy of the apple as it falls?– Potential energy decreases;

kinetic energy increases; total mechanical energy remains the same.

Projectile Motion

• Conversions from kinetic to potential and back to kinetic are taking place.

Energy Transformations in a Swing

• Another good example of kinetic to potential energy transformations.

https://www.youtube.com/watch?v=4B36Lr0Unp4

Law of Conservation of Energy• Energy cannot be created or destroyed, it

simply changes form.• Matter can be converted into energy

through– Fusion—atomic nuclei fusing together

• http://library.thinkquest.org/17940/texts/fission/fission.html

– Fission—atomic nuclei being broken apart• http://www.atomicarchive.com/Fusion/

FusionMov.shtml

Fission vs. Fusion

Fusion

Fission

More on the LAW of Conservation of Energy

• It may seem as though energy is being lost, as with the pendulum example, but some energy is generally lost to FRICTION.– Friction creates thermal energy.– Air resistance (another type of friction) slows

things down.

• GRAVITY is also a factor in stopping motion.

Conserving energy is not the same as

“Conservation of Energy”

• To conserve energy means to not waste energy resources.

• On the other hand, the law of conservation of energy is a universal principal that describes what happens to energy as it is transferred from one object to another or one form to another.

Your Body’s Use of Energy

• Your body stores energy from the foods you eat in the form of fat and other chemicals.

• When your body needs that energy, it will “burn” the fat. In other words, the chemical energy from fat will convert into thermal and mechanical (kinetic) energy.

How Do We Measure Energy in Food?

• The label used for a unit of food energy is the Calorie (note it is capitalized).

• 1 C is equal to about 4,184 Joules.• A gram of fat consumed contains about 9

C. • A gram of carbohydrates or proteins

contain about 4 C of energy.– Carbs include sugars, starches, and fiber

Fat contains the most energy of all foods.