Transcript Types of Energy - Iowa Park High School

Types of Energy
Chapter 11
Review Vocabulary
 System – The object or objects of interest that can
interact with each other and with the outside world.
 Work-energy theorem – Doing work on a system,
the result is a change in the system’s energy.
How is energy used in every day
speech?
 What are some examples you use?
 Food/drinks, athletes in sports, the companies that
supply your home with electricity, gas and heat.
How do scientist and engineers use
the term energy?
 Work is the process that transfers energy between a
system and the external world. When an agent
performs work on a system, the system’s energy
increases, when the system does work on the
surroundings, the system’s energy decreases.
 This chapter looks at mechanical energy.
Can energy change forms?
 Yes. It is like ice cream – there are a lot of varieties,
but they are all types of energy
What diagram is used to show the
transformation of energy?
 Energy Bar diagram – keeps
track of the energy stored or
used
 We will use these diagrams
when we look at the
conservation of energy
Types of Mechanical Energy
 What is kinetic energy?
 The energy that is due to the motion of a system’s
center of mass. Think of it as your moving energy.
 What is potential energy?
 Energy that is stored due to interactions between
objects in a system. There is more than one type of
potential energy. Brain POP
 Energy in Roller Coasters
Describe the work done by gravity as the
orange rises from the juggler’s hand.
 Let h represent the orange’s height
measured from the jugglers hand. On the
way up, its displacement is upward, but
the gravitational force on the orange (Fg)
is downward, so the work done is
negative. On the way back down, the
force and displacement are in the same
direction so work is positive.
Describe the work done by gravity as the
orange rises from the juggler’s hand.
 While the orange moves upward, gravity
does negative work which slows the
orange to a stop. When it goes back
down, gravity does positive work,
increasing the orange’s speed and kinetic
energy.
 At the top, the orange has all GPE. At the
person’s hand, the orange has all KE.
Halfway between these points there is
equal GPE and KE.
Gravitational Potential Energy (GPE).
 Type of Potential Energy
 The stored energy due to gravity.
What is a reference level?
 The position defined
to be zero. If you look
at the picture of the
girl juggling oranges,
you could use her
hands as the
reference level or the
top height of the
orange as a reference
level.
Elastic Potential Energy (EPE)
 The stored energy due to the object’s change in
shape.
 What types of objects have elastic potential energy?
 Springs, rubber bands, trampolines, string on a bow
and arrow.
Albert Einstein
 Recognized that mass is a type of energy called rest
energy (E0).
Other forms of energy
 Chemical and nuclear – the chemical bonds (which store
energy) are broken down. The energy is released when the
structure of the atom’s nucleus changes.
 Thermal Energy– the sum of kinetic and potential energy
of the particles in the system. Ex: rubbing your hands
together.
 Electrical energy – associated with charged particles. Ex.
Power plants
 Radiant energy – energy transferred by electromagnetic
waves.
Mechanical Energy Equations
1
2
 EPE = 𝑘𝑥 2
 k = spring constant
 x = displacement of object (how far it is stretched)
1
2
 KE = 𝑚𝑣 2
 m = mass
 v = velocity
Mechanical Energy Equations
 GPE = 𝑚𝑔ℎ
 m = mass
 g = gravity (we are now using down as positive)
 h = height
 E0 = 𝑚𝑐 2
 m = mass
 c = speed of light (3.0 x 108 m/s)
Unit of Energy
 Energy is measured in Joules (J)
 This make sense because the change in energy is
equal to work.
Conservation of Energy
Vocabulary
 Closed System – A system that does not gain or
lose mass.
 Law of Conservation of Energy – states that in a
closed, isolated system, energy can neither be
created nor destroyed; energy is conserved.
 Mechanical Energy – the sum of the kinetic and
potential energy of the system’s object.
What is the equation that represents
mechanical energy?
ME = KE + PE
Mechanical energy is the sum of kinetic and potential
energy.
Can you use both types of potential
energy to find the mechanical energy of a
system?
 Yes – gravitational and elastic
Match the scenario with the correct
energy bar diagram.
1
2
B
C
3
A
Conservation of Mechanical Energy
 Can mechanical energy be conserved?
 Yes
 What is the conservation of mechanical energy
(KEi + PEi = KEf + PEf)?
 The sum of the system’s kinetic energy and potential
energy before an event is equal to the sum of the
system’s kinetic energy and potential energy after that
event.
If friction is present in a system, is
energy is still conserved? Why?
 Yes, the energy is just transformed into a different
type (non-mechanical energy). Energy cannot just
disappear.
 EX: Friction and air resistance
How do objects in everyday life (roller
coasters, bouncy ball, etc.) stop without
violating the law of conservation of energy?
 Some of the original mechanical energy in the system
transforms into another form of energy within the
system or transmits energy outside the system.
 Ex: warmer = thermal energy, sound = sound energy
What are the problem solving strategies
for conservation of energy?
1. Carefully identify the system.
2. Identify the forms of energy in the system. Identify
which forms are part of the mechanical energy of the
system.
3. Identify the initial and final states of the system.
4. Is the system isolated?
 There are no external forces acting on the system.
 Einitial = Efinal
 If there are external forces, then final energy is the sum of the
inital energy and the work done on the system. Remember,
work can be negative.
 Einital + W = Efinal
What are the problem solving strategies
for conservation of energy?
5. For an isolated system identify the types of energy
in the system before and after. If the only forms of
energy are potential and kinetic, mechanical energy
is conserved.
KEi + PEi = KEf + PEf
6. Decide on the reference level for gravitational
potential energy.
7. Drawing an energy bar diagram showing the initial
and final energies may help.