Transcript Energy and its forms

Energy
Energy
Is defined as the
Ability to do Work
Energy has Two
Types: Kinetic (Energy of Motion)
and
Potential (Stored Energy)
Kinetic Energy
KE = ½ m v
2
Ex: A moving car has
the ability to
do work on the light
pole if it hits it.
Potential Energy
2 possibilities
Gravitational PE Object lifted to some
height
Elastic PE - A stretched
or compressed object
(spring or rubber
band)
Gravitational Potential Energy or
Will it fall?
GPE = m g h
m is the mass of the
object in Kg,
g is the acceleration
due to gravity which is
9.8 m/s2 on earth and
h is the height in meters
Use the formula page!
PE = mgh
41 What is the
potential energy of
the rock?
A 59,900 joules
m = 95 kg g = 9.8 m/s2
B 64,600
joules
h = 100
m
C 93,100 joules
2 x 100 =
95Dkg121,600
x 9.8 m/s
joules
93,100 joules C
Law of Conservation of Energy
• Energy can change forms, but
is never created nor destroyed
• Loss in one form = gain in an
another form
• A falling object speeds up as it
falls to the ground; PE
decreases as KE increases.
The KE it has at impact = the
PE it had before it fell.
Example: A falling object speeds
up as it falls to the ground;
PE decreases as KE
increases, the KE it
has at impact with the
ground is equal to the
PE it had before it fell
Energy can be conserved in
Non-Mechanical forms
The chemical energy in a battery
transforms into electrical
energy
Any reaction where more energy
is given off than is used to start
it is Exogonic
An Endogonic reaction absorbs
energy and causes cooling
Electrical Energy Moving electrons in a path is
electricity
• Electrical Potential Difference (v) is measured in Volts
• The rate of moving electric charges, Electric Current (I),
is measured in Amperes
• Resistance or opposition to the movement of the
energy is called Resistance (R).
Thermal Energy
A body contains internal KE due to the
motion of its atoms ( they are
constantly wiggling and jiggling)
Thermal Energy is the total internal KE
of a body
Temperature is the average KE of a
body
Heat- Transfer of
Thermal Energy
Three forms of heating:
1. Conduction-direct contact, a
pot heating on a stove (solids)
2. Convection- heating by
circulating fluids, (gas and liquid)
heating from a fireplace
And. . .
3. Radiation – Transfer of
Electromagnetic (E.M.) Energy
• Objects are heated
when exposed to
infrared radiation
• The suns heats the
earth by sending
infrared radiation
along with other forms
of E.M. energy 3.0 x
108 meters through
empty space
Heat moves by conduction in solids
since the particles are close together
and vibrate. . .
43 Heat convection occurs in gases and liquids.
Heat convection does not occur in solids
because solids are unable to —
A absorb heat by vibrating
B transfer heat by fluid motion
C emit radiation by reflecting light
D exchange heat by direct contact
Solids do radiate heat to their surroundings
2 The primary way liquids and gases
transmit heat is by the process of —
F reflection
G conduction
H radiation
J convection
Fluid heat movement
is convection. Fluid
motion occurs in
liquids and gases.
50 A solar heater uses energy from the
sun to heat water. The heater’s panel is
painted black to —
Convection is movement of heat in fluid matter, heat loss
improve
emission
radiation
would
be from
a solid
exterior
–infrared
Not Gits
Painting
aF substance
will notofchange
conductivity –
G reduce the
heat lossItby
convection
currents
That is a property
of metals.
would
have to
be made of
H improve
absorption
of that:
infrared
radiation
a different
substance
to change
Not
J
J reduce the heater’s conducting properties
Emission is giving off – we want to absorb: Not F