Science 14: Chapter #7 – Simple Machines and Energy Transfer Baier Science 14
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Science 14: Chapter #7 – Simple
Machines and Energy Transfer
Baier Science 14
7.1- Forms of Energy
Kinetic Energy Energy of motion; all moving objects
have kinetic energy
Ex. A baseball due to its motion
Potential Energy Energy that could be converted into
motion energy
Ex. A bungee jumpers just before they leave the platform
Chemical Energy Energy stored within chemical
bonds
Ex. TNT has chemical energy that it is released when it explodes
Baier Science 14
7.1 - Forms of Energy
Electric Energy
Energy associated with
electricity
Ex. An outlet is a source of
electrical energy
Thermal Energy
Energy in the form of heat
Ex. A stove element is a
source of thermal energy
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7.1 - Forms of Energy
Light Energy
Energy in the form of radiation
Ex. Light bulbs emit light energy
Sound Energy
Energy in the form of sound
waves
Ex. Speakers emit sound energy
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7.1 - Work
Each of these forms of energy can do work.
Work is done when there is any change in the
shape, temperature, speed or direction of an
object
Energy is defined as the ability to do work.
What is Work?
In science, a force is a push or pull.
Work is done when a force moves and object over a
distance.
Baier Science 14
7.1 - Work
Work is calculated using the formula:
W = F∙d
Where: W = work measured in Joules (J or N∙m)
F = force measured in Newtons (N)
d = distance measured in meters (m)
The amount of work done is measured in two ways:
A Newton-metre (N•m) is the work done when one newton of force is used for a distance of one meter.
A Joule (J) is the standard way of reporting work done. One joule is equal to one newton meter. 1 joule = 1 N•m
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7.1 - Calculating Work
Problem: If a force of 5N is applied to an object for 4m, how much work was
done on the object.
Solution: 1. What do you know? What are you trying to find?
d = 4 m
F = 5 N
W =??
2. Substitute into the calculation to find what you are looking for…
The work done on the object is 20J
(5 )(4 )
20
W Fd
W N m
W J
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7.1 - Accomplishing Work
In science, work is done when BOTH of the
following are satisfied:
1. A force is applied to an object.
A cyclist coasting downhill is not work. No force is being
applied by the cyclist to the bike. The force is equal to
zero.
2. The object moves.
A person pushing against a solid wall is not work. The
wall does not move. The distance the object is moved is
equal to zero.
If either of these doesn’t happen work is equal
to zero. Baier Science 14
7.2 - Simple Machines
Simple Machines have only one movement.
Ex. Incline Planes
The movement of an incline plane is a slide or ramp.
The inclined plane or ramp is probably the oldest
machine.
It functions by increasing the distance over which
work is done, thereby reducing the force required to
accomplish the work.
Examples of an incline plane
include:
• Mountain switchbacks
• Loading ramps
• Cork screw / metal bolts Baier Science 14
7.2 - Levers
Levers are bars or planks that pivot on a fulcrum.
The object that the lever moves is the load.
The force required to move the object is the effort.
A –between the load and the fulcrum is the load arm
B- between the fulcrum and the effort is the effort
arm or force arm. Baier Science 14
7.2 - 3 Classes of Levers
First Class Levers
In the first class lever the fulcrum is
between the load and the effort.
Examples of first class levers include: A teeter totter
Prying the lid off a paint can with a screw driver
A pair of scissors
Pliers
A catapult
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7.2 - 3 Classes of Levers
Second Class Levers
In a Second Class Lever there is a bar
with a fulcrum at one end, and effort at
the other end, and a load in between
Examples of a second hand levers include
wheelbarrow, springboard (diving),
nutcracker, a pushup.
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7.2 - 3 Classes of Levers
Third Class Levers
The fulcrum is at one end and the effort is between the load and the fulcrum Third class levers are often used for jobs that
require speed. Examples are: Axes
Rackets for tennis, squash, badmintion
Hockey sticks
Tongs
Brooms
Tweezers
Fishing pole Baier Science 14
7.3 - Pulleys
A pulley is a grooved wheel with a rope or chain running along the groove A pulley is like a class
one lever The load is attached
to one end of the rope, while effort is applied to the other end of the rope. The pulley is the fulcrum.
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7.3 - Compound Pulleys
Combinations of pulleys
are needed to lift very
heavy loads
A combination of pulleys
is called a compound
pulley
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7.3 - Wheel & Axle
A wheel and axle must have two turning
objects attached at their centers, where
if one object turns the other must turn as
well.
Examples:
Faucets
Doorknobs
Steering Wheels
Car/Bike Wheels
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7.3 - Force Ratios
A force multiplier is a simple machine that easily
moves a large load.
A small force on the effort end of the lever puts a large
force on the load.
If the effort end moves a great distance and the
load moves a small distance the machine is a force
multiplier.
Examples of Force Multipliers:
First and second class levers – Crowbars and Wheelbarrows
Most wheel & axles – Doorknobs and Wrenches
Compound pulleys
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7.3 - Speed Ratios
Other machines are distance multipliers
A distance multiplier moves a load through a
large distance but requires a short effort
distance.
Examples:
Third class levers – Hockey Sticks and Fishing Rods
Gears – high gear on a bike
When distance is multiplied, it provides a
speed advantage.
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7.4 - Efficiency
When a machine is used, the machine itself will lose energy through:
Friction between any two moving parts that touch each other.
Heat that is given off by the cooling system or through the exhaust and is therefore not used to do the work.
Poor combustion (if it uses fuel) – when an engine is poorly tuned, some of the fuel is not burned but given off as smoke or carbon particles.
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7.4 - Efficiency
A machine’s efficiency is a comparison of the work the machine does with the energy it uses to do that work.
No machine is 100% efficient. The work output does not equal the work input.
Example: Burning food, the food does not receive all the energy put out by the burner.
Type of
Technology
%
Efficiency
Incandescent
Light Bulbs
5-20
Battery 90
Furnace 70-90
Electrical
Appliances
80-95
Gasoline
Engine
25-40 Baier Science 14
7.4 - Efficiency
The Bigger Problem
Most of the energy used in Canada comes from
burning fossil fuels. There are two
environmental concerns related to the use of
fossil fuels:
1) Burning fossil fuels contributes to global climate
change and air pollution.
2) Fossil fuels are non-renewable.
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7.4 - Efficiency
How can we deal with these problems?
Reduce the amount of energy we use, either by
using machines less or by changing to more
efficient machinery.
Use energy renewable sources
What are two examples of energy efficient
technologies that we could use?
Example in Figures 7.25 – 7.29
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http://www.learntomove.com/images/content/movingup/using-ramp.jpg
http://www.beth.k12.pa.us/schools/wwwclass/mcosgrove/simplemachines.gif
http://home.insight.rr.com/jkmckee/lever.jpg
http://www.ent.ohiou.edu/~bobw/html/HapEd/NASA/SimpMach/cl2lever.gif
http://www.sciencebyjones.com/third_class_lever_drawing.gif
http://www.fitstep.com/Advanced/Anatomy/Graphics/triceps-anatomy.jpg
http://users.snip.net/~veraandscience/Work/Fixed.gif http://users.snip.net/~veraandscience/Work/Movable.gif
http://etc.usf.edu/clipart/25700/25757/fixed_pulley_25757_lg.gif
Baier Science 14
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