Transcript Chapter 4-- Energy

Chapter 4-Energy
Section 1: The Nature of Energy
 What is Energy—
 Energy is present all around us all
day
 Energy changes are taking place
constantly
 Ex: baseball flying and hitting a
window, combing your hair, walking
to class, etc
 Energy is the ability to cause change
 Anything that causes change must
have energy
 There are many different forms of
energy including electrical, chemical
and thermal
Kinetic Energy
 -is energy in the form of motion
 Ex: spinning wheel, sprinting runner,
football passing through goalposts
 Amounts of Kinetic Energy depend on
two quantities: mass and velocity
 (more mass = more energy)
 (more velocity = more energy)
Calculating Kinetic Energy
 The equation for calculating kinetic
energy is:
 Kinetic energy = ½ mass X
velocity^2
 Joule—the SI unit of energy
Potential energy
 -is stored energy due to position
 Objects that have potential energy
have the ability to cause change
 Elastic Potential Energy= energy
stored by something that can stretch
or compress (ex: rubber band)
 Chemical Potential Energy = energy
stored in chemical bonds (ex: atoms)
Gravitational Potential Energy
(GPE)
 Gravitational Potential Energy is
energy stored by objects that are
above Earth’s surface
 The amount depends on the MASS of
the object, Acceleration Due to
Gravity and HEIGHT above the
ground
 GPE = mass X 9.8 m/s/s X height
 (GPE is measured in Joules also)
Section 2: Conservation of Energy
 Transforming electrical energy
 Happens all day, everyday
 Ex: lightbulbs transform electrical
energy into light
 Some of the electrical energy is turned
into thermal energy (hot bulbs)
 Ex: alarm clock, straighteners, toaster,
etc.
Transforming chemical energy:
 Fuel is stored in the form of chemical
potential energy
 Ex: Engines transform chemical potential
energy stored in gas into kinetic energy
 Ex: Green plants convert light energy from the
Sun into stored energy in chemical bonds
Conversions between kinetic and
potential energy
 Many situations involve conversions
between potential and kinetic energy
 Ex: bicycles, roller coasters, swings,
etc.
 Mechanical energy is the total
amount of potential and kinetic
energy in a system
 Mechanical energy = GPE + KE
 When energy is transformed from
potential to kinetic, the potential
energy is not LOST, it has simply
been converted, but the total amount
of energy remains the same
 Ex: Pg. 109—apple tree, baseball,
swing
Law of Conservation of
Energy:
 Kinetic and potential energy are
constantly changing as the object
speeds up and slows down
 However, mechanical energy (total
energy) stays constant
 So: -Energy cannot be created or
destroyed, it simply changes form
Friction and the Law of
Conservation of Energy
 Friction slows moving objects, which
seems to decrease mechanical energy
of an object.
 However, friction converts energy to
other forms such as thermal energy
(heat)
Converting Mass into Energy
 Nuclear fusion—a special kind of
energy conversion
 During this process a small amount of
mass is transformed into a
tremendous amount of energy by
fusing atomic nuclei (sun)
 Nuclear fission—similar process, but
nuclei are broken apart, not fused
together
Human Body –Energy
Conversions
 Complex chemical and physical
processes in the body obey the law of
conservation of energy
 Energy is stored as fat and converted
to energy as needed for life processes
 1 Calorie (C) is equal to 4,184 J
 Every gram of fat supplies 9 C of
energy
 Section 2 Assessment questions