Transcript Notes: Ch. 6 Energy and Power

Notes: Ch. 6 Energy and Power
What is energy?


The ability to do work or
cause change is called
energy.
Work can be thought of
as the transfer of
energy.
Kinetic Energy




The energy of motion is called kinetic energy.
The kinetic energy of an object depends on
both its mass and its velocity.
Kinetic energy increases as mass increases.
Kinetic energy increases as velocity
increases.
Potential Energy
Energy that is
stored or held in
readiness is
called potential
energy.
Ex.
Food
a boulder at the
top of a mountain
Elastic Potential Energy



The potential energy
associated with objects
that can be stretched or
compressed is called
elastic potential energy.
Ex. a stretched rubber
band
A squished spring
Gravitational Potential Energy

Potential energy that depends on height is
gravitational potential energy.

Ex. a book on a desk
Different Forms of Energy

Mechanical energy is the energy associated
with the motion or position of an object.

Ex.
a frog leaping
a car moving
Different Forms of Energy

Thermal energy is a measure of the energy of the
particles in an object.
Ex.
ice
cream melting
Different Forms of Energy

Chemical energy is
potential energy
stored in chemical
bonds that hold
compounds together.

Ex. the food you eat
Gasoline
Different Forms of Energy


Electrical energy is energy associated with
moving electric charges.
Ex.
power in power lines
Different Forms of Energy





Electromagnetic Energy is a form of radiant
energy, which travels in waves.
Ex.
visible light
Microwaves
Infrared radiation
Ultraviolet radiation
Nuclear energy is stored in the nucleus of
an atom and is released during reactions.
Ex. nuclear power
in a power plant
The sun and other
stars
Conversions Between Forms of Energy


A change from one form of energy to another
is called an energy conversion. Most forms
of energy can be converted into any other
form.
ex. a toaster converts electrical energy into
thermal energy
Kinetic and Potential Energy





One of the most common conversions is from
kinetic to potential energy and back.
Ex. Energy Conversion in an Earthquake
Ex. Energy Conversion in a Waterfall
Ex. Energy Conversion in a Pole Vault
Ex. Energy Conversion in a Pendulum
Conservation of Energy


According to the law of conservation of
energy, energy cannot be created or
destroyed.
So what happens to the energy in a
pendulum? Why does it slow down?
The mechanical energy of the moving
pendulum is transformed into heat
energy due to friction. So, it is not
lost, but converted.
A little change….

Einstein changed the law of conservation of
energy with his theory of relativity. He said
that energy can sometimes be created, but in
order to do so, matter must be destroyed.
Therefore,
scientists say that energy and
matter together are always conserved.
Conserving Energy


Conserving energy means saving it, or not
wasting it.
Ex. Not wasting fossil fuels.
Photosynthesis

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The process through which plants make food
is known as photosynthesis.
Photo = “light”
Synthesis = “putting together”
During photosynthesis, white light
(electromagnetic energy) is converted into
food (chemical energy).
The Nature of Light

The sun is the source of energy on Earth.
There are three things that can happen to light.
It can be:

Transmitted (allowed to pass through)

Reflected (bounced off)

Absorbed (taken in)
Plants and Light


Plants absorb some colors of the visible
spectrum and reflect others. They have
pigments that absorb different colors of light.
The colors that are not absorbed (green) are
reflected. This is why plants usually appear
green.
Chlorophyll is the pigment that gives plants
their green color. It absorbs most blue and
red light, and reflects the green part of the
spectrum.
Energy Conversions in Photosynthesis
Photosynthesis is the process through which
plants convert the radiant energy of the sun
into chemical energy.
 Capturing the Sun’s Energy
Photosynthesis begins when chlorophyll and
other pigments capture the sun’s radiant
energy.


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Using Energy to Make Food
Water and Carbon dioxide are combined with
the radiant energy to create a sugar that the
plant uses for food.
The chemical formula for this is……
carbon dioxide
6CO2
+
water
6H2O
Light energy
→
glucose
C6H12O6
+
+
oxygen
O2
Glucose and Stored Energy

The breakdown of glucose in a plant, is
called respiration. This is when the chemical
energy is released. It is similar to digestion
in humans.
Fossil Fuels



A fuel is a material that releases energy
when it burns.
A fossil fuel is an energy-rich substance
formed from the remains of organisms.
This energy was stored as potential energy
when the plants of that time converted the
sun’s radiant energy into chemical energy.
Using Fossil Fuels

The process of burning fuels is known as
combustion. Today in coal burning power
plants, coal is burned to heat water, which
creates steam that runs turbines . These
turbines are connected to generators which
produce electricity.
 The
energy conversions look like
this:
Chemical energy → thermal →
mechanical → electrical
Fossil Fuels