Transcript Work and Energy

Integrated Science
Unit 2, Chapter 5
Unit Two: Work and Energy
Chapter 5 Work, Energy and Power
5.1
Work
5.2
Energy Conservation
5.3
Energy Transformations
Chapter 5 Learning Goals

Calculate the amount of work done by a simple
machine.

Use units of joules to measure the amount of work
done.

Analyze the effects of changing force or distance in a
simple machine.

Calculate the efficiency of a machine.

Calculate power in machines.

Discuss perpetual motion machines.
Chapter 5 Vocabulary Terms

chemical energy

electrical energy






law of conservation of
energy

nuclear energy

potential energy watt

power work

radiant energy

radiation

solar power
energy transformations
heat efficiency
horsepower
joule energy
kinetic energy
5.1 The Meaning of Work
 The
—
—
—
—
 If
word work is used in many different ways.
You work on science problems.
You go to work.
Your toaster doesn’t work.
Taking out the trash is too much work.
you push a box with a force of one newton
for a distance of one meter, you have done
exactly one joule of work.
5.1 Work
Work (joules)
Force (N)
W=Fxd
Distance (m)
5.1 Efficiency
 In
a very efficient machine, all (or most) of the
work input becomes work output.
 An
engineer would say the machine was 100
percent efficient, because all the input work
became output work and none was lost.
 You
calculate efficiency by dividing the work
output by the work input.
5.1 Power

The rate at which work is done is called power.

You can determine the power of a machine by dividing the
amount of work done by the time it takes in seconds.

The unit of power is called the watt.

One watt is equal to one joule of work done in one second.

Another unit of power commonly used is the horsepower.

One horsepower is equal to 746 watts.
5.1 Power
Power (watts)
Work (joules)
P =W
t
Time (sec)
5.1 Work
Key Question:
What happens when you multiply forces in
machines?
5.1 Mini Quiz
1.
How is work defined in science?
2.
What are the units of work?
3.
What is meant by an efficient machine?
4.
What is power?
5.
What are the units of power?
5.2 Energy


Energy is the ability to do work.
Any object that has energy has the ability to
create force.
 Energy

is measured in the same units as work.
A joule is a unit of force that acts over a
distance.
5.2 Potential Energy
 The
first type of energy we will explore is
called potential energy.
 Potential
energy comes from the position of an
object relative to the Earth.
 Objects
that have potential energy don’t use
their energy until they move.
5.2 Potential Energy
Mass (kg)
Potential Energy
(joules)
Ep = mgh
Height (m)
Acceleration
of gravity (m/sec2)
5.2 Kinetic Energy
 Objects
 Energy
also store energy in motion.
of motion is called kinetic energy.
 Applying
a force means you do some work,
which is stored as energy.
 Kinetic
energy depends on two things: mass
and speed.
5.2 Kinetic Energy
Kinetic Energy
(joules)
Ek = 1 mv2
2
Mass (kg)
Speed (m/sec)
5.2 Energy Conservation

Nature never creates or
destroys energy; energy only
gets converted from one form
to another.

This concept is called the law
of conservation of energy.

At any moment in its flight, the
ball has exactly the same
energy it had at the start.

The energy is divided between
potential and kinetic, but the
total is unchanged.
5.2 Energy Conservation
Key Question:
What is energy and how
does it behave?
5.2 Mini Quiz
1.
What is energy?
2.
What are the units of energy?
3.
What is potential energy?
4.
What is kinetic energy?
5.
What is the law of conservation of energy?
5.3 Energy Transformations
Energy transformations
occur between different
types of energy.
— radiant energy
— electrical energy
— chemical energy
— nuclear energy
5.3 Energy Transformations

On a trip up a hill, work is
transferred to potential.

Potential is transferred to
kinetic on the way down
the hill.

The total energy is
conserved.
Energy Transformations
in a Power Plant
Power plants convert
chemical energy into
electrical energy.
1. chemical energy
2. heat energy
3. mechanical energy
4. electrical energy
5.2 Other Forms of Energy

Radiant energy is also known as electromagnetic
energy.

Electrical energy we use in our daily lives is actually
derived from other sources of energy.

Chemical energy is the type of energy stored in
molecules.

Nuclear energy comes from splitting an atom, or
fusing two atoms together.

Heat is a form of thermal energy.
5.3 Energy Transformations
Key Question:
Where did the energy go?
5.3 Mini Quiz
1.
What is mechanical energy?
2.
How does potential energy get used up?
3.
What is radiant energy?
4.
What is nuclear energy?
5.
What is thermal energy?