Name
Class
Date
Packet # 3
Why Do We Use Machines?
4-1 What is work?
YOU WILL LEARN:
o To identify when work is being done on an object.
o To calculate the amount of work done on an object.
Key Terms
work: the action that results when a force causes an object to move in the direction of the force
joule: unit of work (equal to Newton x meter)
power: amount of work done per unit of time (the rate at which work is being done)
Lesson Summary
• Work is done when a force moves an object a certain distance.
• For work to be done on an object, the direction of the object’s motion must be the same direction of
the force.
• Work can be calculated by multiplying force by distance. Work = Force x distance
• Power is the measure of how much work is done in a given amount of time.
• Power can be calculated by dividing the amount of work by the time taken to do that work.
Power = Work ÷ time
Explain why lifting a box is work, but carrying the box across the room is not work?
4-2 What is a machine?
YOU WILL LEARN:
o To explain how machines make work easier.
o To give examples of how to increase machine efficiency.
Key Terms
machine: device that makes work easier
work input: the work done on a machine (usually by a person)
work output: the work done by the machine
mechanical efficiency (eh-FIHSH-uhn-see): the percent of work that the machine puts out compared to
the work put into the machine
mechanical advantage: number of times a machine multiplies the input force
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
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Energy and Work: CHAPTER 14
Lesson Notes, page 1
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Lesson Summary
• A machine makes work easier by changing the size or direction (or both) of a force.
• The force you apply to a machine is called the input force. The force the machine applies is the
output force.
• When a machine changes the size of the force, the distance that the force is applied must also change.
• Mechanical advantage tells how many times a machine multiplies the input force. Mechanical
advantage is equal to output force divided by input force.
Mechanical Advantage = Output Force ÷ Input Force
• Mechanical efficiency is a comparison of a machine’s work output with work input. Mechanical
efficiency is equal to work output divided by work input and is expressed as a percentage.
• Machines are not 100 % efficient because some of the work done by a machine is used to overcome
friction. Work output is always less than work input.
What are some machines that you use every day to make work easier?
4-3 What are simple machines?
YOU WILL LEARN:
o To identify and give examples of 6 types of simple machines.
o To describe the mechanical advantage of simple machines.
o To identify the simple machines that make up a complex
machine.
Key Terms
lever (LEV-uhr): a simple machine made of a bar that pivots at a fixed point, called a fulcrum
inclined plane: a simple machine that is a straight, slanted surface; a ramp
wedge: a simple machine that is a double inclined plane that moves; a wedge is often used for cutting
screw: a simple machine that is an inclined plane wrapped in a spiral
wheel and axle: a simple machine made of two circular objects of different sizes; the wheel is the larger
of the two circular objects
pulley: a simple machine made of a grooved wheel that holds a rope or a cable; there are two
kinds of pulleys – fixed and movable
compound machine: machine that is made of two or more simple machines
Lesson Summary
• All machines are constructed using six simple machines.
• Compound machines consist of two or more simple machines.
• Compound machines have low mechanical efficiencies because they have more moving parts and
thus more friction to overcome.
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Energy and Work: CHAPTER 14
Lesson Notes, page 2
Name
Class
Date
When does work happen?
For each example identify if the example IS work or is NOT work.
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Energy and Work: CHAPTER 14
Lesson Notes, page 3
Name
Work =
Class
Date
x
Therefore, the amount of work done depends on how much
over how much
.
Who is doing more work below?
Explain:
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Energy and Work: CHAPTER 14
Lesson Notes, page 4
Name
Class
Date
4-1 How can work be measured?
Lesson Review
Use the equation Work = Force × Distance to answer the following questions.
Units for WORK:
Force (Newtons) x Distance (meters) = Newtons x meters = Joules
1. A horse with a force of 50 N pulls a cart of wood a distance of 10 m. Calculate the amount of work
done.___________________________________________________________________________________
2. Leroy pushes his car with a force of 5 N. However, the car does not move. How much work has
Leroy done? ____________________________________________________________________________
3. A truck pushes a mound of dirt 5 m with a force of 100 N. How much work has been done?
_______________________________________________________________________________________
4. A horse performed 170 J of work pulling a cart of wood 10 m. How much force was used?
_______________________________________________________________________________________
Skill Challenge
Use the diagrams to answer the following questions. Show your work when
calculating work
1. Which numbers are unnecessary when calculating work? _____________________________________
2. Calculate how much work is being done in Figure 1. _________________________________________
3. In Figure 2, the force given is the force that each man exerts. What is the total amount of force on
the car? ________________________________________________________________________________
4. How much work is being done in Figure 2? _________________________________________________
_______________________________________________________________________________________
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Energy and Work: CHAPTER 14
Lesson Notes, page 5
Name
Class
Date
Do machines change the AMOUNT of work being done?
Look at the diagram below. 3 characteristics change in the arrows below. What does each
changing characteristic mean?
For each example below, write what the machine is changing from input to output force.
Person’s work in
Machine’s work out
Explain how
force is
changed in
each
example.
lever
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Energy and Work: CHAPTER 14
Lesson Notes, page 6
Name
Class
Date
Lever: A rigid object (bar) that is free to rotate (move) around a fixed point called the fulcrum
Wheel & Axle: Two different sized cylinders that rotate together around the same point. The
axle is the small, inner cylinder and the wheel is the larger outer cylinder.
Pulley: A grooved wheel with a rope wrapped around it.
Inclined Plane: A flat, slanted or sloped surface.
Screw: An inclined plane wrapped around a center rod.
Wedge: Two inclined planes back to back.
Directions: Arrow and label as many simple machines as possible in
each of the following diagrams.
lever
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
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Energy and Work: CHAPTER 14
Lesson Notes, page 7
Name
Class
Date
4 – 3 Bicycles and Simple Machines
Skills: interpreting diagrams, relating concepts
PART A A bicycle is a familiar compound machine. The diagram below shows
how various simple machines make up the parts of a bicycle. Refer to the
diagram as you answer the questions.
1. List the basic simple machines that make up a bicycle. ________________________________________
_______________________________________________________________________________________
2. How does a simple machine make a hand brake work? _______________________________________
_______________________________________________________________________________________
3. Gears are special types of wheels that have interlocking teeth. Where are gears located in a bicycle?
_______________________________________________________________________________________
4. A larger gear will turn a smaller gear more times than it turns itself. The gears on the rear wheel are
smaller than the gears on the pedal. What does this tell you about the number of times the bicycle
wheel will turn compared with the number of times you have to turn the pedals? ________________
_______________________________________________________________________________________
_______________________________________________________________________________________
5. Why is this relationship of the gears important to the speed of the bicycle? ______________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Energy and Work: CHAPTER 14
Lesson Notes, page 8
Name
Class
Date
Finding Machines in Everyday Life
In this unit you learned about work and how machines can help make all kinds
of work easier. You saw examples of simple machines and compound machines.
Directions:
• In the drawing below, find as many machines as you can, and classify
them as simple or compound.
• For each simple machine, write what type of simple machine it is.
/ type of
simple
machine
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
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Energy and Work: CHAPTER 14
Lesson Notes, page 9