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## Energy

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### Energy How we use our resources – PowerPoint PPT presentation

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Title: Energy

1
Energy
• How we use our resources

2
Discussion
• What are five (5) ways you use energy every day?

3
What is energy?
• Energy is the capacity to do work or produce heat.

4
Which form do I use?
• Kinetic energy energy due to motion the
mechanical energy that a body has by virtue of
its motion
• Potential energy the energy available to move
matter the mechanical energy that a body has by
virtue of its position
• Radiant Energy energy being transferred between
objects by electromagnetic waves. energy that
exists in the absence of matter

5
Types of Energy
• Energy is the capacity to do work.
• Chemical
• Heat
• Sound
• Mechanical
• Electrical
• Light

Potential Energy Energy stored in chemical
bonds.
Kinetic Energy energy due to an objects motion.
Radiant Energy electromagnetic waves
6
Units of Measurement for Energy
• calorie the amount of heat needed to raise the
temperature of one gram of water by one degree
Celcius.
• Joule - The joule (symbol J), named for James
Prescott Joule, is the derived unit of energy in
the International System of Units.
• 1 joule kg x m2 / s2

7
SI units for energy is the Joule(J)
• 1 cal 4.184 J
• Convert 250.2 calories to J.
• Convert 42.5 J to cal.
• Convert 25000 KJ to cal.
• Convert 142.6 Kcal to J

8
How is energy used?
• You tell me, name the ways we use energy every
day.

9
Heat or Temperature?
• Heat is defined as the transfer of energy from
one object to another. Heat is transferred from
an area of high to low (hot to cold).
• Heat is measured in BTU, Joules or calories
• Temperature is the measure of how hot or cold an
object is.
• Temperature is measured in F, C or K

10
Boy its hot in here!
• When energy in the form of heat is transferred
through an object or a fluid, it is called
conduction.
• When energy in the form of heat is transferred
directly from one object to another it is called
• When energy is transferred by a displacement of
molecules, it is called convection.

11
Move it or lose it!
• High to low
• A hot air mass will move toward a cold air mass.
• Heat does not rise as much as it is moving in
an effort to warm the cold air above it.
• Where does the heat come from on the ground?

12
Thermodynamics
• Thermodynamics is the study of the flow or
exchange of energy .
• System
• Surroundings

13
1st Law of Thermodynamics
• The 1st Law of Thermodynamics is the Law of
Conservation of Matter (Energy)
• Energy is neither created nor destroyed, it
simply changes form.
• Dr. Pepper (chemical) into movement (mechanical)
• In any chemical reaction there is an exchange of
energy.
• The net energy in the entire universe is constant.

14
3rd Law of Thermodynamics
• The 3rd Law of Thermodynamics states that the
entropy of a pure perfect crystal is zero (0) at
zero Kelvin (0 K).
• no object or system can achieve a temperature of
zero Kelvin

15
2nd Law of Thermodynamics
• The 2nd Law of Thermodynamics states that in any
spontaneous change, the entropy of the universe
must increase which means that the quality of
energy deteriorates gradually over time.
• Entropy is the measure of randomness or disorder
in a system and is also a measure of unusable
energy within a closed or isolated system

16
Implications of the 2nd Law
• During a chemical reaction, energy is converted
from one form to another.
• There is also a certain amount of energy that is
converted into heat. Heat is a form of energy of
lower quality and not as usable
• chemical ? mechanical ( heat)

17
Gravitational Influence
• Energy that is stored in the gravitational field
is called gravitational potential energy, or
potential energy due to gravity.

18
Gravity Works!
• If the object is being lifted at constant
velocity, then it is not accelerating, and the
net force on it is zero. We know that from
Newton's first law of motion.
• We must pull up on an object when we lift it. So,
the agent doing the lifting must provide an
upward force on the object.

19
Its Not All Apples!
• Gravity, of course, will be pulling down. This
pull down of gravity is called the weight of the
object.
• If during the lift the net force on the object is
zero, then the upward pull must be canceled by
the downward pull. That is, the upward lifting
force must be equal in size to the downward pull
of gravity.

20
Summary of Gravity
• In summary, when you are lifting something at
constant velocity, the upward pull that you
provide is equal to the weight of the object.

21
Gravitational Potential Energy
• Since the work done on the object when it is
lifted becomes the gravitational potential
energy, the formula for gravitational potential
energy equals the mass of the object times the
acceleration due to gravity times the height
that the object is lifted, as in
• Ug mgh

22
Example
• Ug mgh Formula for gravitational potential
energy.
• Ug (4 kg)(9.8 m/s/s)(5 m) Plug in values for
mass, acceleration due to gravity, and height.
• Ug 196 J Gravitational potential energy equals
196 Joules.

23
Energy Efficiency
• The term energy efficiency refers to the measure
of the useful energy.
• An energy efficient appliance would convert the
energy supplied to it with a minimal amount of
heat returned as energy.

24
The Components
• Input is all components (matter and/or energy)
entering the system.
• Throughput is the flow of all components within
the system.
• Output is all components leaving the system.

25
Measure of Efficiency
• The efficiency of a product can be measured by
• efficiency (output / input) x 100
• output is mechanical work or energy (watts or
joules)
• input is the quantity of work or energy
• Cannot exceed 100 because of the Law of
Conservation of Energy

26
Calculate the Efficiency of Bouncy Balls
• Measure the efficiency of a bouncy ball, a golf
ball and a tennis ball.
• Which ball converts energy more efficiently?
• How is this conversion of energy helpful for the
use of the ball?

27
Specific Heat Capacity
28
Specific Heat Capacity
• Specific heat is the amount of energy needed to
raised 1 gram of a substance by 1 degree Kelvin
or Celcius.
• Energy is in the form of heat.
• High specific heat means that a lot of energy is
needed to heat or even melt a substance.
• Can you think of an example of a high specific
heat?

29
The Formula
• Specific Heat cp q / m ?T
• q heat and is measured in Joules
• m mass and is measured in grams
• ?T the change in temperature and is determined
taking the final temperature and subtracting the
initial temperature
• T final T initial

30
Water
• Water has a relatively high specific heat
• 4.18 J / g K
• Water holds heat well that is why the
temperature on the water is more consistent than
the temperature on the land.

31
Problems
• How much energy is needed to heat a 100g pan of
water from 25C to 95C?
• m 100g
• cp 4.18 J/gK
• ?T 95C 25C 70C
• cp q / m?T and when you rearrange the formula
• q cp m ?T