Transcript Chapter 7 Work and Energy PowerPoint

Ms. Brown
8th Grade General Science
Jennifer C. Brown
 Energy is the ability to “do work” and describes the ability
of things to change or cause change in other things.
• Work is done when a force moves an object over a distance.
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You do 1 joule of work
if you push with a
force of 1 newton
for a distance of 1
meter.
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(joules- J)
(N)
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(m)
How much work is done by a person who
pulls a cart with a force of 50 newtons
if the cart moves 20 meters in the
direction of the force?
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 The
origin of energy in the universe is
unknown.
• Most Scientists
think it was created
during the big bang.
 Scientists
believe that the total amount of
energy and matter in the universe is
constant. *What does
this
mean?*
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 This
law states that energy can be neither
created nor destroyed. It can only be
transformed from one type into one or more
other types of energy (heat may be
released).
Mechanical
Energy
(Sound)
Electrical
Energy
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1) Mechanical
Spinning Fan
2) Chemical
Burning Candle
3) Nuclear
Nuclear Reactor
4) Heat
Toaster
5) Electrical
Generator
6) Light
Lamp (bulb)
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

Question: Where Does Candle Wax Go?
Answer: Have you ever noticed how you
have less candle after burning than
before? This is because the wax oxidizes
(burns) in the flame to yield water and
carbon dioxide, which dissipate in the
air around the candle, in a reaction
which also yields light and heat.
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

Based on what we know
about energy, machines
allow us to do incredible
things.
A machine is a device with
moving parts that work
together to accomplish a
task.
Initially, we invented simple
machines like levers to
accomplish tasks.
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 Mechanical
energy is the energy with
which moving objects perform work.
• Hammer striking a nail
• Jack lifting a car
• Pedals turning wheels of bicycle
• Sound
• You striking a match
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 Sound
Energy:
• Sound is a form of energy produced by a
vibrating object.
• When an object vibrates, it moves rapidly back
and forth, moving (expanding & compressing)
the air around it and forming sound waves.
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• The substance that sound travels through is
called the medium.
• Can sound waves travel through a vacuum?
 No, because there are no particles to transmit it.
• Similar to light, in what form do you think sound
travels in?
 Waves
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 Important
Parts of a Wave:
• Wavelength – the distance from one point in a
wave to a corresponding point in the next wave.
• Amplitude – the height of the crest measured
from the undisturbed surface.
• Frequency – the number of waves that pass by a
fixed point in a given amount of time.
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2
Main types of waves:
• Transverse Wave – vibrates up and down at a
right angle to the direction in which the wave is
traveling. ( shown by a rope moving up and
down).
• Longitudinal Wave – vibrates back and forth
within its direction of travel.
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 Chemical
energy is the energy stored in
certain substances because of their chemical
makeup. (ex. = batteries, foods, propane gas)
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 The
energy stored within the nucleus of
an atom. This energy can be released by
joining atoms together or by splitting
atoms apart.
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 The
energy produced by the molecular
motion of matter. (ex. – rubbing hands
together, burning a match..)
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 Produced
by the flow of electrons
through a conductor, such as a wire. (ex. –
computers, televisions …)
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A
form of radiant energy that moves in
waves. (ex. – magnifying light, laser eye
surgery…)
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 Potential
Energy:
• The stored energy
of an object as a
result of its position.
 Kinetic
Energy:
• The energy of
motion (vertical or
horizontal)
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Equations:
• Potential Energy
 (in Joules)
Ep = m x g x h
mass (m) x gravity (g) x height (h)
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• Kinetic Energy
 (in Joules)
Ek =
2
½mv
mass (m) x velocity (v)
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 The
speed of sound depends primarily
on what 2 factors?
• The medium through which it is passing
 Denser medium = faster speed of sound
• The temperature
 Colder temperature = faster speed of sound
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 Number
the mediums from fastest speed
of sound to lowest speed of sound:
Medium
Iron
Water
Air
Glass
State
1
3
4
2
Solid
Liquid
Gas
Solid
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 Light
is a visible form of energy.
• Travels in waves
• Travels in straight paths called rays
• Unlike sound waves, however, light rays cannot bend
around objects.
• When light strikes a surface:
 Reflected
 Absorbed
 Transmitted
 The
smoother the surface, the more accurate
the reflection. (mirror)Jennifer C. Brown
 Transparent
Materials:
• Ex – window glass
• Permit almost all of the incoming light to pass through.
 Translucent
Materials:
• Ex – wax paper
• Let some light pass through but scatter the light so it isn’t
clear.
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 Refraction
• When light waves are
bent when passing
through two media of
different densities, such
as from water into air.
• This is how a lens is
made.
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A
Lens
• A piece of transparent glass or plastic that has curved
surfaces.
 Convex Lens – (surface curves outward) Bends light rays so
they are focused in toward a common point.
 Concave Lens – (surface curves inward) Bends light rays so
they spread out.
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 The
Electromagnetic Spectrum
• Light waves are a part of a larger group of energy
waves that can travel through a vacuum called
electromagnetic waves.
• Electromagnetic Waves:
 Radio waves
 Microwaves
 Infrared waves
 Visible light
 Ultraviolet rays
 X rays
 Gamma rays
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