CHAPTER 13: WORK AND ENERGY

SECTION 3: WHAT IS ENERGY?

ENERGY AND WORK• WHENEVER WORK IS DONE, ENERGY IS TRANSFORMED OR IS TRANSFERRED

FROM ONE SYSTEM TO ANOTHER SYSTEM

• DEFINITION OF ENERGY: THE ABILITY TO DO WORK

• ENERGY COMES IN MANY FORMS:

• NUCLEAR

• CHEMICAL

• MECHANICAL

• HEAT

• SOUND

• ENERGY IS MEASURED IN JOULES (J)… JUST LIKE WORK!

The ones we are talking about in physical science.

TYPES OF MECHANICAL ENERGY

POTENTIAL ENERGY

• THE ENERGY THAT AN OBJECT HAS BECAUSE OF THE POSITION, SHAPE, OR CONDITION OF THE OBJECT.

• TWO TYPES:

• ELASTIC POTENTIAL ENERGY

• GRAVITATIONAL POTENTIAL ENERGY

KINETIC ENERGY

• THE ENERGY THAT AN OBJECT HAS DUE TO THE OBJECT’S MOTION

𝑃𝐸𝑔= h𝑚𝑔

𝐾𝐸=12𝑚𝑣2

Total mechanical energy = PE + KE

MORE ABOUT POTENTIAL ENERGY

• SOMETIMES THIS TYPE OF ENERGY IS REFERRED TO AS STORED ENERGY

• ELASTIC POTENTIAL ENERGY DEPENDS ON HOW STRETCHED OR COMPRESSED THE OBJECT IS

• GRAVITATIONAL POTENTIAL ENERGY DEPENDS ON

• THE MASS OF THE OBJECT

• THE RELATIVE HEIGHT

• RELATIVE TO WHERE THE REFERENCE POINT IS DEFINED

MORE ABOUT KINETIC ENERGY

• KINETIC ENERGY DEPENDS ON

• THE MASS OF THE OBJECT

• HOW FAST THE OBJECT IS MOVING

• BECAUSE VELOCITY IS SQUARED, KE DEPENDS ON SPEED MORE THAN MASS

• ATOMS AND MOLECULES HAVE KINETIC ENERGY, BECAUSE THEY ARE ALWAYS MOVING.

OTHER FORMS OF ENERGY

• CHEMICAL REACTIONS INVOLVE POTENTIAL ENERGY

• PHOTOSYNTHESIS IS THE PROCESS THAT TURNS ENERGY FROM THE SUN INTO CHEMICAL ENERGY THAT IS STORED IN SUGARS AND OTHER MOLECULES IN CELLS

• WHEN YOU EAT, YOU ARE EATING STORED ENERGY… POTENTIAL ENERGY

• THE SUN GETS ENERGY FROM NUCLEAR REACTIONS, CALLED NUCLEAR FUSION

• ENERGY CAN BE STORED IN FIELDS

• EARTH’S GRAVITATIONAL FIELD STORES GRAVITATIONAL POTENTIAL ENERGY

• ELECTRIC FIELDS STORE ELECTRICAL ENERGY