Bell Ringer
 What is work?
Work, Power,
& Machines
What is work ?
 The product of the force applied to an
object and the distance through which
that force is applied.
Is work being done or not?
 Mowing the lawn
 Weight-lifting
 Moving furniture up a
flight of stairs
 Pushing against a
locked door
 Swinging a golf club
 YES
 YES
 YES
 NO
 YES
Calculating Work
All or part of the force must
act in the direction of the
movement.
Eureka work
Do you do more work
when you finish a job
quickly?
 Work does NOT involve time, only force
and distance.
 No work is done when you stand in place
holding an object.
 Labeling work: w = F x d
 Unit of Work: Newton X meter (N m)
The Joule
 1 newton-meter
is a quantity
known as a
joule (J).
 Named after
British physicist
James Prescott
Joule.
 How quickly work is done.
 Amount of work done per unit time.
 If two people mow two lawns of equal
size and one does the job in half the
time, who did more work?
 Same work. Different power exerted.
 POWER = WORK / TIME
The watt
 A unit named after
Scottish inventor
James Watt.
 Invented the steam
engine.
 P = W/t
 Joules/second
 1 watt = 1 J/s
watts
 Used to measure
power of light
bulbs and small
appliances
 An electric bill is
measured in
kW/hrs.
 1 kilowatt = 1000 W
Horsepower (hp) = 745.5
watts
 Traditionally associated with engines.
(car,motorcycle,lawn-mower)
 The term horsepower was developed to
quantify power. A strong horse could
move a 750 N object one meter in one
second.
750 N
Math Review
 Work Equation
 Power Equation
 Work=Force x distance  Power = Work / time
To solve for something else use triangle. Cover up what you are solving
or looking for and make the equation with what you are given (know).
Math Practice
 You must exert a force of 4.5 N on a
book to slide it across the table. If you do
2.7 J of work in the process, how far
have you moved the book?
 A light bulb does 100 joules of work in
2.5 seconds. How much power does it
have?
 A man exerts 700 newtons of force to
move a piece of furniture 4 meters. If it
takes him 2 seconds to move the
furniture, how much power does it
require?

 A hair curling iron uses 13 watts of
power. How long must it operate to do
1,040 joules of work?
 A 4-watt night light is left on for 8 hours
each night. How much work does it do
per night?
 A force of 100 newtons was necessary to
lift a rock. A total of 150 Joules of work
was done. How far was the rock lifted?
 A set of pulleys is used to lift a piano
weighing 1,000 newtons. The piano is
lifted 3 meters in 60 seconds. How much
power is used?
 What is the power of a kitchen blender if
it can perform 3,750 joules of work in 15
seconds?
 A deflated hot-air balloon weighs a total
of 8000 N. Filled with hot air the balloon
rises to a height of 1000m. How much
work is accomplished by the hot air
balloon?
Question?
 Give the units for the following
measurements:
1.
2.
3.
4.
Distance
Force
Work
Power
Machines
 A device that makes work easier.
 A machine can change the size, the
direction, or the distance over which a
force acts.
Forces involved:
 Input Force  Output Force
FO
FI
Force
Force
applied
by
applied to
a machine
a machine
Two forces, thus two
types of work
 Work Input
 work done on a
machine
=Input force x the
distance through
which that force acts
(input distance)
Work and Power video
 Work Output
 Work done by a
machine
=Output force x the
distance through
which the resistance
moves (output
distance)
Can you get more work
out than you put in?
Work output can never be greater than
work input.
Mechanical Advantage (MA) –
expressed in a ratio WITH
NO UNITS!!
 The number of times a machine
multiplies the input force.
MA = Fout/Fin
2 types of mechanical
advantage
 IDEAL (IMA)
 Involves no
friction.
 IMA =dE /dR
 E = effort
 R = resistance
 ACTUAL (AMA)
 Involves friction.
 AMA=FR / FE
Efficiency
 Efficiency can never be greater than 100 %.
Why?
 Some work is always needed to overcome
friction.
 A percentage comparison of work output to
work input.
Efficiency(%) = work output (WOut) / work input (WIn) X
100%
Simple Machines Chart –
create a 7x4 chart titled
Simple Machines
Machine
Description
Mechanical
Advantage
Examples
Simple Machines Gallery
Walk
 The class will be split into groups. Each group will
choose a simple machine and create a poster of that
machine. Each poster MUST HAVE the following
information:
1. Name of your simple machine
2. Picture or drawing
3. Description of how it works
4. Description of how to determine mechanical
advantage
5. Examples and uses in everyday life (you can bring in
an example for Extra Credit)

You have 30 minutes to create your poster then
we will walk around the gallery to observe the other
machines and record the information in your charts.
1. The Lever
 A bar that is free to pivot, or move about
a fixed point when an input force is
applied.
 Fulcrum = the pivot point of a lever.
 There are three classes of levers based
on the positioning of the effort force,
resistance force, and fulcrum.
Identify the fulcrum, effort
force & resistance force
First Class Levers
 Fulcrum is located
between the effort
and resistance.
 Makes work easier
by multiplying the
effort force AND
changing direction.
 Examples:
IMA = Lin / Lout
Second Class
Levers
 Resistance is found
between the fulcrum
and effort force.
 Makes work easier
by multiplying the
effort force, but NOT
changing direction.
 Examples:
Third Class Levers
 Effort force is located
between the
resistance force and
the fulcrum.
 Does NOT multiply
the effort force, only
multiplies the
distance.
 Examples:
Levers!!!!!!!!!!!
2. The Wheel and
Axle
 A lever that rotates in
a circle.
 A combination of two
wheels of different
sizes.
 Smaller wheel is
termed the axle.
 IMA = rwheel/raxle.
3. The Inclined
Plane
 A slanted surface
used to raise an
object.
 Examples: ramps,
stairs, ladders
 IMA = l(m)/height(m)
Can never be less
than one.
4. The Wedge
 An inclined plane
that moves.
 Examples: knife, axe,
razor blade
 Mechanical
advantage is
increased by
sharpening it.
5. The Screw
 An inclined plane
wrapped around a
cylinder.
 The closer the
threads, the greater
the mechanical
advantage
 Examples: bolts,
augers, drill bits
6. The Pulley
 A chain, belt , or rope
wrapped around a
wheel.
 Can either change
the direction or the
amount of effort force
 Ex. Flag pole, blinds,
stage curtain
Pulley types
 FIXED
 Can only change
the direction of a
force.
 MA = 1
 MOVABLE
 Can multiply an
effort force, but
cannot change
direction.
 MA > 1
MA = Count # of ropes that
apply an upward force (note
the block and tackle!)
Fe
 A combination of two or more simple
machines.
 Cannot get more work out of a compound
machine than is put in.
Physical Science
Chapter 16
Thermal Energy
& Heat
Physical Science Physics Project

Rube Goldberg – Honda Accord Ad

This Too Shall Pass – Rube Goldberg –
State Farm
Thermal Energy
Sometimes called
internal energy
 Depends on the
object's mass,
temperature, and
phase (solid, liquid,
gas)
 TOTAL potential and
kinetic energy of all
the particles in an
object

Heat

vs.
The spontaneous flow
of THERMAL energy
from a hot object to a
cold object
Temperature

A measure of the
AVERAGE kinetic
energy of the
particles in an object
Let’s compare Temp, Thermal Energy, & Heat!!
Temperature – a measure of the AVERAGE
kinetic energy of the individual particles of a
substance.
 Thermal energy – TOTAL energy of all of the
particles
 Heat – THERMAL energy moving from a warmer
object to a cooler object, trying to reach
thermodynamic equilibrium.

Which of
these can we
measure?
Thermal energy vs. temp
Now remember that thermal energy,
unlike temperature, depends on mass
 Compare a cup of tea and a teapot full of
tea, both at the same temperature

– Is the average kinetic energy the same in
both?
 YES!
– Which has more thermal energy and why?
 The teapot because it has more particles (mass)!
Thermal energy

Which has more thermal energy?
– Pitcher of cool lemonade or cup of hot tea?
– Pot of boiling water or an iceberg?
Balloon demo
Need 2 balloons: 1 filled with air, 1 filled with water
Matches
Student volunteer
So, how do thermometers work?
Thermal expansion and contraction
 Particles move faster and expand as they
warm
 So, as the temperature increases, the
alcohol in the tube expands and its height
increases
 Heat and temperature - thermometers

Absolute zero- that temperature where the individual particles contain no
more energy. The particles (atoms and/or molecules) cease vibrating. No
movement occurs.
Absolute Zero
-459
o
-273
o
0
o
Section 16-1
Review p.478



In which direction does heat flow on its own
spontaneously?
Name 2 variables that affect the thermal energy of an
object.
Why is it necessary to have regularly spaced gaps
between sections of a concrete sidewalk?
Thermodynamics
Heat Transfer
Heat moves in only one direction: from a
warmer object to a cooler object
 Two drinks in the same room:

The hot coffee __________ to room temp
because . . .
 The iced tea _______ to room temp
because . . .

– Hot coffee cools to room temp because the
heat of the coffee is transferred to the cooler
temperature of the room.
– A cold glass of Iced tea soon warms up to the
surrounding room temperature because the
warmer temperature of the room’s
surroundings is transferred to the colder glass
of iced tea thereby warming it up.
Heat Transfer

Heat is transferred in one of three ways:
– Conduction
– Convection
– Radiation

Specific Heat Video
Conduction

Conduction – heat is transferred from one object to
another by direct contact.
– Examples include: a metal spoon in hot water gets
hot or a pot gets hot as it sits on an electric stove.
– Fastest in solids. Much slower in gases. Why? (think
about collisions)
Conductors vs. Insulators
Conductor – a material that transfers heat
well: metal, tile, glass
Insulator – a material that does not transfer
heat well: air, carpet, wood, wool
Conductors vs. Insulators animation
Conductors vs. Insulators activity

Why does a tile floor feel colder than a
wood floor, even though they're both at
room temperature?
– The tile feels colder because it is a better
conductor and transfers thermal energy
rapidly away from your skin.

Why does a thick wool sweater keep you
warm?
Convection

Convection – the transfer of thermal energy when
particles of a fluid move from one place to another….the
particles transfer the heat.
– Examples include: a pot of boiling water sets up
convection currents to move the hot water at the
bottom of the pot being heated to the cooler water at
the top of the pot, convection currents in a heated
room keep the temperature uniform.
Convection of warm air
Air is heated by sunlight
 The temperature of the air

– Increases

The air
– Expands

The less dense air
– Rises

The denser air
– Sinks
Radiation

Radiation – transfer of energy by electromagnetic waves.
– Examples include: the Sun’s energy traveling through
space and heating up the Earth w/out heating space
itself, Heat lamps used at fast food restaurants, and
the radiator of a car dissipating the heat of an engine.
What type of heat transfer is
represented by each arrow?
Heating Systems




Central heating systemsuse convection to
distribute heat
Radiators-steam, and
boilers- water
Put heat into the air it
rises, circulates, then falls
Controlled by a bimetallic
thermometer
Cooling Systems
Heat pumps- reverse
the flow of heat
energy
Refrigerant- fluid that
vaporizes absorbing
heat and condenses
when giving off heat
Must do work to reverse
flow of heat energy
Refrigerator
Puts cold air into
warm
 Heat coil beneath
fridge releases
heat produced by
the work

Heats the outdoor air
 Warm air flows from
inside the house into
the AC, then as heats
is removed from coil
cold air is created

Air Conditioners