Transcript ModifiedInvestigation 1

Investigation #1
Getting To Work With Energy
Investigating How Forces Transfer Energy
ENERGY
What is ENERGY?
What do you think of
when you hear the word
ENERGY?
Why is energy so important to us?
What types of energy do you encounter most often?
How does energy get from one place to another?
ENERGY defined …
• Energy is typically defined by the
CHANGE that is caused when
energy changes form or moves
form one object to another object.
• The unit of measure for Energy is
Joules (J)
Types of Energy Forms
Mechanical Energy
Kinetic Energy (KE) - the energy of motion.
The energy associated with moving objects is
called kinetic energy (KE), and is often referred to
as the most fundamental form of energy. The
size of the KE is determined by an object’s speed
and its mass. A moving baseball has kinetic
energy. If you have ever been hit by a pitched
ball, you are aware of the energy a moving object
can have.
Give three examples of other objects that may
have kinetic energy.
Gravitational Potential Energy (GPE)
• - the energy of position. This is energy that
an object possesses due to its position. The
size of the GPE is determined by the object’s
mass and its height above the ground. A
person climbing a ladder increases her height
above the ground, she increases her GPE.
•
Give three examples of objects with
gravitational potential energy.
Heat Energy (HE)
- the random kinetic energy of particles. Heat energy is the
random, and very disorganized, kinetic energy of the particles in a
substance. Thermal energy is another term often used as a
synonym for heat energy. In most cases the distinction between
the exact definitions of heat energy and thermal energy is not
made.
Due to the random nature of this form of energy, it is difficult to
make heat energy a useful form of energy. For this reason it is
usually the form of energy that appears at the end of energy
chains. It happens so often that scientists refer to heat energy as
the “graveyard of energy”. For example, if you pound a nail into a
piece of wood, the nail gets hot due to the energy transferred to it
by the hammer and the force of friction with the wood.
Give three examples of objects that have thermal
energy.
Chemical Potential Energy (CPE)
the energy of bonds. Chemical potential energy,
sometimes just called chemical energy, is the energy stored
in the bonds that hold the particles in a substance together.
When these bonds are formed, or are broken, energy
transfers and/or transformations take place. In many cases,
the energy stored in the bonds of substances is transformed
into other forms of energy. Food is a source of chemical
energy for our bodies, so we sometimes use ‘food energy’ in
place of chemical energy in energy chains that involve
people. In most cases this chemical potential energy is later
transformed into heat energy
-
Give three other examples of chemical potential energy.
Electromagnetic Energy
- the energy of waves. This form of energy is often referred to as solar
energy and light energy as well. Electromagnetic energy is the energy that is
carried by electromagnetic waves. The most common form of electromagnetic
energy is “light”. Light energy is a term that can be used to describe the
energy ranges that our human eyes are sensitive to and it may include some
forms of ‘light’ that we can not see with our eyes, such as infrared and
ultraviolet. The sun is the most important source of electromagnetic energy,
supplying the vast majority of our planet’s energy. In some cases, chemical
potential energy can be transformed into electromagnetic energy. This form of
energy is very important in the scientific field of astronomy.
Electrical energy is a subset of electromagnetic energy, characterized by
moving charges. It is used to run appliances and make artificial light. When
the charged particles vibrate, they transfer energy by electromagnetic waves.
Give three other examples of electromagnetic energy.
Sound Energy
- the
energy of vibrating particles. This form of energy is transferred by
mechanical waves. The particles that make up a substance vibrate in a highly
organized manner and transfer energy through the substance. The particles in the
substance vibrate, but do not change their location. In most cases, sound energy is
classified into three categories; infrasonic is the sound that is below our human
hearing level, sonic is the sound that our human ears are sensitive to, and ultrasonic
is the sound that is above our human hearing level. Have you ever made a tin can
telephone? If so, you have already experimented with sound waves and how
vibrations are involved in the energy transfer process.
A good example of the use of sound waves is sonar. Humans have created devices
that enable us to send out a sound wave and listen for the echo so that we can
determine how far away something is to the source. Seismic waves or “earthquake”
waves also fit into this category because they involve the transfer of energy through
vibrating matter in the form of mechanical waves. Ultrasounds in the medical field
are used for a variety of purposes. Perhaps you have seen an ultrasound image of a
baby. In most energy chains, the sound energy is transformed into heat energy (the
disorganized and random KE of particles).
Give three other examples of sound energy.
Elastic Potential Energy (EPE)
- energy
of deformed materials. This form of energy comes
from the stretching or compressing of elastic materials. When
an elastic material is deformed (by stretching or
compressing), it exerts a force, called the elastic force, to
return to its original shape. In many cases, the elastic
material is held temporarily in this deformed position and the
material has a stored amount of energy.
Bow hunters make use of EPE to shoot their arrows. The
EPE of the bow string is converted to the KE of the arrow.
Catapults and slingshots also operate in this manner. Tennis
players rely on the elastic properties of their tennis racquets
and the tennis ball. Pole vaulters depend on the stored
energy in the bent pole to help them get over the bar. The
science behind the design of the pole relies on knowledge of
how material store EPE. Surprisingly, certain types of rock
can have elastic properties. They can be stretched or
compressed under huge forces.
Give three other examples of elastic potential energy.
Dropping Golf Balls ...
You will drop the golf
ball from four different
heights looking for
evidence of energy by
a change that is
produced.
Investigation Reflection:
•
Question #1: Does the golf ball have energy while it is sitting
on the top of the sand? (Assume that the sand represents the
ground)
Pick up the golf ball and hold it about 20 cm above the pan.
•
Question #2: What type of energy does the golf ball have
while the ball is being held at a height of 20cm above the pan?
•
Question #3: How did the golf ball get its energy? Where did
this energy come from?
Release the ball and discuss the crater produced by the golf
ball.
Repeat the process from 40 cm, 80 cm, and 100 cm (1m). Discuss why the craters are larger as the height increases; what
we see is a greater CHANGE. Drop each trial’s ball in a different spot in the sand so that they can be compared in
the end.
•
Question #4: Which trial created the most change in the sand
(the largest crater)?
Introduce a hollow practice golf ball into the investigation. Repeat the same process as was done with the
solid golf ball.
•
Question #5: What variable was changed in this part of the
investigation? What effect did this change have on the crater
in the sand?
•
Question #6: Did the hollow ball and the solid ball impact the
sand with the same speed? In other words, did gravity speed
them up both golf balls at the same rate?
•
Question #7: What can you conclude from our investigation?
The height and weight of the ball influences the GPE.
Heavier and higher goes up lighter and lower goes down.
•
Energy Transfer vs. Energy Transformation
• Energy TRANSFER is the passing of
energy from one object to another
object.
• Energy TRANSFORMATION is the
changing of energy from one form of
energy to another form of energy.
Energy Chains
• Energy chains are graphical
representations of the flow of
energy in a system.
• They typically contain words,
phrases, and images.
Law of Conservation of Energy: Energy can not be created nor destroyed. Energy can be transferred
from one object to another and can be transformed from one form to another, but the total amount of
energy never changes.
Forces That Transfer Energy
Making Crash Barriers
Investigating How Forces Transfer Energy
Part A: Creating a Barrier
Focus Question: What barrier design will stop the car in
the
shortest distance?
Your task is to create a stopping barrier out of dominoes that
will stop the car in the shortest distance possible.
Pre-Investigation Questions
•
Question #1: What form of energy is present when the car is
sitting at the top of the ramp? How do you know this?
•
Question #2: What will happen to the energy of the car as it
moves down the ramp? What evidence could you collect to
justify your answer?
•
Question #3: When the car strikes the barrier what will
happen to the energy of the car? How do you know this?
•
Question #4: Let’s assume we release the car from rest at
the top of your ramp. What can you do to be sure that the car
strikes your barrier with the same KE in each trial? Explain.
Conduct your Investigation
Record your results carefully and be prepared
to report to the class the design of your barrier
that stopped the car in the shortest distance by
exerting the largest stopping force and the
answers to the questions asked below.
• Question #5: What forces are causing the car
to stop?
• Question #6: Why is the stopping distance
shorter for some arrangements of blocks than
for other arrangements?
Stopping Distances:
Investigating How Forces Transfer Energy
Part B: Creating a Safe Stopping Barrier
Focus Question: What is the shortest distance that your
car
needs to safely stop the moving car?
Your task is to create a stopping barrier out of dominoes that
will stop the car safely (the domino passenger can not fall
over or out of the car) in the shortest distance possible.
Stopping Distances:
Investigation Reflection:
• Question #7: How did the smallest “safe”
stopping distance from Part B compare to the
stopping distance in Part A?
• Question #8: Can you think of other
materials that would make safer barriers than
the ones you made out of blocks? Explain
why you think these other materials would
make safer barriers?
WORK
The Transfer of Energy
How does the previous investigation help us to
understand how forces transfer energy?
SAFER Crash Barriers
An excellent application of these concepts is the “soft walls”
used by major racing facilities across the nation (Dover
International Speedway being one of these). The new
SAFER (Steel And Foam Energy Reduction) barriers have
revolutionized the sport of automobile racing and made it
much safer for both the drivers and the fans.
So how do SAFER barriers absorb energy?
The barriers move upon impact so that the KE of the car is transferred to a very
large area of the wall (a large portion of the wall flexes upon impact). The key idea
is that no one portion of the wall receives a large amount of the car’s KE. The KE of
the flexing soft wall is then transferred to the outer permanent wall and support
structure. The materials that make up the wall are not elastic.
Imagine what the collision would be like if the wall was elastic! Still other portions of
the car’s initial KE are transformed into heat energy and sound energy.