Download Chapter 4 Energy

Chapter 4
Energy
Section 1: The Nature of Energy
What you will learn:
• Definition of energy, different forms of energy.
• How to calculate kinetic energy.
• How to calculate gravitational potential energy.
• Every change that occurs-large or small- involves energy.
• When something is able to change its environment or
itself, it has energy.
• Energy is the ability to do work or cause change.
What is energy?
• Energy has several different forms-mechanical, heat,
chemical, electromagnetic (or radiant), nuclear.
• The SI unit for energy is the Joule.
Different Forms of Energy
• Mechanical: energy that is associated with
moving parts.
• Heat: caused by the motion of particles. This
causes changes in phase and temperature.
• Chemical: energy required to hold atoms
together. This is released when bonds are
broken.
Different Forms of Energy
• Electromagnetic: energy associated with moving
charges. Includes electricity, visible light, x-rays, radio
waves, microwaves, and ultraviolet.
• Nuclear: released in the form of heat and light when the
nucleus of an atom undergoes fission (splitting) or
fusion (joining together). The sun’s energy is produced
from nuclear fusion.
Different Forms of Energy
• Kinetic energy is the energy of motion.
• The formula for kinetic energy is half of the mass times
the velocity squared:
Kinetic Energy
• If Julie is running with a speed of 4 m/s and her mass is
60 kg. How much kinetic energy does Julie have?
Example
• How much mass does a turtle have if he is moving with
1.2 m/s and has 84 J of kinetic energy?
Example
• Even motionless objects can have energy. This is stored
energy.
• Stored energy is referred to as potential energy, it depends
on the position of the object.
• There are several different types of potential energy, for
example: elastic potential energy, chemical potential
energy, and gravitational potential energy.
Potential Energy
• Common examples of elastic potential energy are a
stretched rubber band and a spring.
• Elastic potential energy is energy stored by something
that can stretch or compress.
Elastic Potential Energy
• Energy stored in chemical bonds is chemical potential
energy.
• Energy is stored in the bonds that hold the carbon and
hydrogen atoms together and is released when gas from
your car is burned.
• In this chemical reaction, chemical potential energy is
released.
Chemical Potential Energy
• Anything that can fall has stored energy.
• Gravitational potential energy (GPE) is energy stored by
objects due to their position above Earth’s surface.
• Gravitational potential energy can be calculated from this
equation:
• g=9.8 m/s/s remember this is due to Earth’s gravity.
Gravitational Potential Energy
• If Charles throws a bucket that has a mass of 10 kg onto a
truck bed that is 2.4 m tall, how much gravitational
potential energy does the bucket have?
Example
• If a boulder is on top of a hill that is 10.3 m high and it
has 356 J of potential energy, how much does the boulder
weigh? What is the mass of the boulder?
Example
• Energy is the ability to cause _____________.
A. change
B. heat
C. motion
D. work
Summary Question 1
• Energy is the ability to cause _____________.
A. change
B. heat
C. motion
D. work
Energy is the ability to cause change and has several different forms.
Summary Question 1
• What are the five forms of energy?
Summary Question 2
• What are the five forms of energy?
Mechanical, heat, chemical, electromagnetic (radiant),
nuclear
Summary Question 2
• The kinetic energy of an object depends on ___________.
A. the object’s mass and speed
B. the object’s mass
C. the object’s speed
D. the acceleration of the object
Summary Question 3
• The kinetic energy of an object depends on ___________.
A. the object’s mass and speed
B. the object’s mass
C. the object’s speed
D. the acceleration of the object
Kinetic energy depends on both mass and speed of the moving object.
Summary Question 3
Section 2: Energy Conversions
What you will learn:
• How different objects convert one type of energy into the form of
another.
• What the law of conservation of energy is.
• How to calculate total mechanical energy in a closed system.
• Energy conversions are changes in the forms of energy.
• KE to PE – examples are running up a hill or throwing a
ball
• PE to KE – examples are an object falling or a pendulum.
• All other forms of energy can be converted into other
forms; electromagnetic, chemical, mechanical, heat, and
nuclear.
Energy Conversions
• A battery converts chemical energy into electrical energy.
• A light bulb converts electrical energy into heat & light
energy.
• An internal combustion engine converts heat energy into
mechanical energy.
• A solar cell converts light energy into electrical energy.
• A body converts chemical energy into heat & mechanical
energy.
Energy Conversions
• The law of conservation of energy states that energy can
be neither created nor destroyed by ordinary means. It can
however be changed from one form into another.
• In other terms the total energy of any closed system is
constant.
• Mechanical Energy (ME) is the sum of the kinetic and
potential energy of the system.
• ME=KE+PE
Law of Conservation of
Energy
https://www.youtube.com/watch?v=mhIOylZMg6Q
• Mechanical energy is the total amount of ___________ in
a system.
A. kinetic energy
B. momentum
C. potential energy
D. potential and kinetic
Summary Question 4
• Mechanical energy is the total amount of ___________ in
a system.
A. kinetic energy
B. momentum
C. potential energy
D. potential and kinetic
Mechanical energy is the energy due to position and motion of all
objects in a system.
Summary Question 4
• State the law of conservation of energy.
Summary Question 5
• State the law of conservation of energy.
The law of conservation of energy states that energy cannot
be created or destroyed.
Summary Question 5
• Friction converts ______ energy into ______ energy.
A. electrical, thermal
B. mechanical, thermal
C. thermal, electrical
D. thermal, mechanical
Summary Question 6
• Friction converts ______ energy into ______ energy.
A. electrical, thermal
B. mechanical, thermal
C. thermal, electrical
D. thermal, mechanical
Friction converts mechanical energy into thermal energy.
Summary Question 6