Energy

Ch. 15

Forms of Energy Energy is the ability or capacity of

any physical system to do work Work is done by forces Kinetic Energy – energy in motion Potential Energy – energy at rest or

stored energy Any form of energy can be

converted into another form

Types of Energy

Thermal – a.k.a. heat energy Electrical – from forces of the

electrical charges of subatomic particles (p & e)

Light – radiant energy (makes up the electromagnetic spectrum)

Nuclear – stored in the bonds of an atom’s nucleus (given off by breaking or creating those bonds)

Transformation

Changing one form of energy into another

Ex: Hydroelectric dams use generators to transform the kinetic mechanical energy of falling water into kinetic electrical energy

Law of Conservation of Energy

Energy is neither created nor destroyed, it is changed from one form to another

In a closed system, the amount of energy remains constant. (Ex: the cells in your body)

In an open systems, energy is lost to heat and other transformations.

Explained by James Prescott Joule

Chemical & Mechanical

Chemical potential energy is stored in the nutrients in food – your cells transform it into kinetic energy

Some of this energy is changed into mechanical energy (Ex: when your brain sends a signal to move your muscle)

Changes into Mechanical Energy

When you speak – mechanical energy in your breath is changed into sound energy by your vocal chords

Nerve cells transform chemical energy into electrical energy that transmits nerve signals to parts of the body

When you eat, chemical energy from food is turned into thermal energy (heat energy)

Other animals do this too…

Electric eels – use electrical energy to stun their prey or keep predators away with powerful shocks

Fireflies – transform chemical energy into light energy

Other uses…

Thermal energy keeps us warm when its cold outside

When a match is struck, friction transforms mechanical energy into enough thermal energy to ignite the match

Chemical energy stored in the wood of the matchstick changes into more thermal energy as the wood burns

Mass related to energy…

The more mass an object has, the more energy it can absorb

Ex: The ocean’s huge mass absorbs a tremendous amount of heat during the summer & releases it during the winter – this helps keep coastal climates more moderate during both seasons

Lava lamps…

Transform electrical energy into light energy, mechanical energy, and thermal energy.

These transformations happen all day every day, in our bodies

and all around us

Mechanical Energy…2 parts

Kinetic energy Potential energy ME = KE + PE

Kinetic Energy Energy in motion KE = ½ • m • v2

KE = ½ mass • velocity2

Figure it out… What is the K.E. of a 10 kg mass

moving w/ a velocity of 10 m/s? KE=½ mv2

KE=½ (10 kg) (10 m/s)2

KE=500 kg•m2/s2

1 kg•m2/s2 =1 J KE=500 J What if you double the mass? What if you double the velocity?

Potential Energy Energy at rest = potential to move PEg = m • g • h g = gravitational acceleration = ? PEg = mass • 9.8 m/s2 • height Always measured in reference to the

height Different types of potential energy Involves mass, gravity, & height

Figure it out… What is the PE of a 10 kg rock on top of

a 100 m hill? PEg = m g h

PEg = (10 kg) (9.8 m/s2) (100 m)

PEg = 9800 kg • m/s2 • m PEg = 9800 J

Reminder

ME = KE + PE N = kg • m/s2

J = N • m Acceleration due to Gravity = 9.8

m/s2

Ch 14 & 15 Review Work, Power, Energy

Formulas W = F • d P = W / t PEg = m • g • h KE = ½ • m • v2

Facts

IMA vs. AMA Why? Newton’s laws of motion 1st

2nd

3rd

.

More facts

Work is done only if there is movement

How do we arrive at a number for amu of an element?

Covalent vs. Ionic bonds How do they form? Which ones

pair up? Co = NM & NM I = M & NM

More facts

Law of Conservation of Energy ? Chemical change vs. Physical

Change