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 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

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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