5.2 – Conservation of Energy

Write what is in WHITE

Objectives

Describe how energy can be transformed from one form to another.

Explain how the mechanical energy of system is the sum of the potential and the kinetic energies.

Discuss the law of conservation of energy.

Changing Forms of Energy

Light bulb Light & HeatElectrical Radiant & Thermal

Changing Forms of Energy

Fuel Moving CarChemical Potential Thermal

Electric spark ignites fuelThermal Kinetic

Gases expand and move parts of engine

Less Obvious Changes

Green plants convert sunlight into energy stored in chemical bonds

Eating corn (chemical potential energy) becomes other forms of energy in your body

Kinetic & Potential Energy

Bikes, Roller coasters, Swings, Rubber Bands all involve Kinetic & Potential Energy

Mechanical energy is the total amount of potential and kinetic energy

in a system

Mechanical Energy

Energy due to the position and motion of an object or objects in a system

mechanical energy = potential energy + kinetic energy

Falling Objects

Object has gravitational potential energy due to Earth pulling it down

Object becomes loose and accelerates downward due to gravityLoses gravitational potential energyTransformed into kinetic energy as speed

increases

Projectile

Kinetic & Gravitational Potential Energy are converted between each other as ball rises and falls Kinetic Energy gets ball moving Kinetic Energy converted into GPE as ball rises GPE greatest at peak of path GPE converted back to Kinetic Energy as it moves

downward and increases speed

Swing

• Push gets you moving• KINETIC ENERGY

• Swing rises & loses speed• Kinetic changes into GRAVITATIONAL POTENTIAL

ENERGY

• Greatest at top of path

• Swing accelerates downward• GPE changes into KINETIC ENERGY

Law of Conservation of Energy

Energy cannot be created or destroyedEnergy simply changes from one form to

another, but total amount of energy never changes

Why don’t we always see conservation?

Friction & Air Resistance cause mechanical energy to be converted into thermal energyThat’s why chains get hot on a swing

Energy not created or destroyed, but changed into a new form

Nuclear Fusion

Sun’s energy Light & Heat on EarthSmall amount of mass is transformed

into tremendous amount of energyCombining of 2 or

more small nuclei into

one larger nucleus

In the reaction shown here, the nuclei of the hydrogen isotopes deuterium and tritium undergo fusion.

Nuclear Fission

Splitting of one large nucleus into 2 or more smaller nuclei

Power Plants create electrical energy using fission

Human Body

Chemical Potential Energy maintains body temperatureExcess given off as heat to environment

CPE fuels processes such as heart beat and food digestionEnergy is converted into heat and

movement

Human Body

Obeys Law of Conservation of Energy

To maintain a healthy weight you must have a balance between energy consumed and energy usedExcess energy can be stored

as fat

Food Energy

Chemical Potential Energy1 food Calorie (C) = 4,184 Joules

1 gram fat = 9 Calories1 gram of carbohydrates & proteins = 4 C

In-Class Assignment/Homework

5.2 WKT