Drexel-SDP GK-12 ACTIVITY
Activity Template
Subject Area(s)
Data analysis & probability, measurement, number & operations, physical science,
science & technology
Associated Unit
Simple Machines
Associated Lesson
Wheel and Axle
Activity Title
“Rolling, Rolling”
Grade Level
6th-8th
Time Required
2 class periods
Group Size
3 students per group
Expendable Cost per Group
US $10
Summary
Students will learn how friction can significantly slow down an object depending on the
surface it is on. They will record their observations as they move objects across
different surfaces using a force spring gauge. Besides different surfaces, students will
get an opportunity to use a combination of wheels and axles to move their objects
across the surface faster and with less work. Additionally, the activity will end by picking
the best design of wheel and axle to move the instructor across the classroom.
Engineering Connection
Engineers must understand the uses of the wheel and axle to move heavy object across
different surfaces with minimum work. They also must understand the force of friction
so they can minimize it while designing different machines. This activity presents
students with a challenge of moving a person across the room. As engineers, students
must learn how to quickly analyze the problem to come up with the most appropriate
solution.
Keywords
Simple machines, wheel and axle, work, friction, effort, resistance
Educational Standards
• Science: 3.4.7.C
• Science: 3.4.10.C
• Science: 3.7.7.B
• Math 2.2.8.A
• Math: 2.7.8. B
Pre-Requisite Knowledge
• Definition of wheel and axle
• Understanding the work equation (Force x Distance)
• Interpreting a force spring gauge
Learning Objectives
After this lesson, students should be able to:
• Learn how a wheel and axle can make work much easier
• Recognize how textures on a surface change the amount of friction
• Calculate the coefficient of static friction for different surfaces
• Calculate the amount of work needed to move an object across a surface
Materials List
Each group needs:
• Book
• Weighing scale
• String
• Toy Wooden Karts
• 5 wooden rods (1 inch diameter)
• 5 wooden rods (3 inch diameter)
• Metric ruler
• Spring scale
• Calculators
• Stopwatch
• Wooden plank
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Introduction / Motivation
I suggest introducing this lesson with a short clip from The Flintstones cartoon series in
which Fred Flintstone starts up his stone wheel vehicle with his feet. There are a couple
of good friction examples in these scenes. I would first ask the class if they can identify
the places in the clip where friction is exhibited. First of all when Fred first gets in the
car he has to start the car by pushing off his feet. This is an example of using force to
break the static friction. The force from his feet must be stronger than the static friction
holding the stone wheel in place. Once Fred has the car in motion he can rest his feet
for a while because the wheels are already in motion. On the other hand, if he did not
pedal again the vehicle would come to a stop because the stones are constantly turning
over the rough ground, causing the car to slow down. This is an example of kinetic
friction. Finally, whenever Fred wants to stop the vehicle he has to apply the brakes or
as he does it by dragging his feet into the ground. This is an example where his feet
are causing a large amount of friction on the ground.
Vocabulary / Definitions
Word
Definition
Effort
A force exerted by a machine or by the muscles in humans
Resistance The opposition to a force such as the weight of an object
Work
A quantity in physics that relates the amount of force over a certain
distance.
Power
Another quantity in physics that relates the amount of work done in a
certain amount of time.
Friction
A force that resists motion when two objects are in contact
Procedure
Background
Friction can best be explained by relating it to students pushing a heavy box over the
rough ground. The rougher a surface is or the heavier the box is the harder it will be to
move the box, or in other words the more friction that exists. Friction is a force that
resists motion when two objects slide past each other. The weight of the box and the
tiny imperfections on the ground make it difficult to move. In actuality there are
molecular bonds that form and break when two surfaces rub against each other
producing thermal energy in the form of heat. At this point you can have the students
rub their hands together briskly until they feel the heat. That is friction!
Now if one really needed to move a heavy box then they could put wheels under it. This
would reduce the amount of friction created between the two surfaces because a wheel
makes less contact with the ground than a whole box. In the modern era cars can move
through the streets because their rubber tires easily roll on the asphalt. This is because
the two surfaces will produce minimum friction between each other. These two surfaces
are relatively smooth when they slide past each other. It will be important in this lesson
to determine which surfaces will produce the least amount of friction between each
other.
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The force of friction that prevents an object from moving can be expressed by finding
the coefficient of static friction, µ. This value can be found by knowing the weight of the
object or the normal force, W, and the amount of force that is needed to break the
stillness, f.
µ= f / W
Before the Activity
• Review work (Force x Distance) equation with the students.
• Explain the meaning of work, power and friction in terms of physics. Students will
often relate these terms to their everyday experiences.
• Make sure the force spring gauges have hooks on them so they can be tied to the
string.
With the Students
1. Put the book on the weighing scale and record the weight of the book
2. Tie string around the inside pages of a heavy textbook.
3. Hook spring gauge to the end of the string.
4. Place meter stick across table marking the beginning and end of 1 meter.
5. Drag book across the table along the 1 meter path you marked in step 3.
6. Use your stopwatch to record how long it takes to move the book across the surface
(Figure 1).
Figure 1: Book on top of wooden toy kart before dragging across table.
7. Record the force needed to move the book on your worksheet.
8. Calculate the work needed to move the book across the table and record it on your
worksheet.
W=F*D
Where W is the work required to move the object in Newtons-meters, F is the force on
the spring gauge needed to move the object (Newtons), and D is the distance moved. If
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you measured your distance on the ruler in centimeters then remember to divide by 100
to make sure you are in the right units.
W = (F * D) / 100
9. Calculate the coefficient of static friction and record it on your worksheet.
µ= f / (9.8 * W)
where µ is the coefficient of static friction, W is the weight of the object in kilograms and
f is the force on the spring scale needed to move the book in Newtons.
10. Drag the book again for 1 meter but this time over the rug of the classroom.
11. Repeat steps 1-10 using the thin rods, thick rods, and the toy wooden carts (Figure
2).
Figure 2: Picture of friction activity supplies: wooden rods and toy karts.
12. Calculate the power on your worksheet
P=W/t
Where P is the power required to move the object in Watts, W is the work done on the
object in Newton-meters and t is the time needed to move the object in seconds.
13. Based on the work calculated on your worksheet which was the most efficient
method for moving the book?
Now students will get a chance for the fun activity of moving the instructor across the
room.
1. Each group of students will line their track over 5 meters. Students can choose to
use the wooden karts, the rods, or a combination of everything.
2. The instructor will then balance himself on top of the wooden plank which will be on
top of the group’s track.
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3. Instructor will be placed at the starting position.
4. Instructor will be moved across 5 meter distance while the students record the time
and force required to move.
5. Students will determine which method was the best way to move the instructor
across the room.
Table 1: Work done by wheel and axle table.
Trial
Surface
Distance
(m)
No
Medium
Wood
Table
1
No
Medium
Carpet
1
Thin
Rods
Wood
Table
1
Thin
Rods
Carpet
1
Thick
Rods
Wood
Table
1
Thick
Rods
Carpet
1
Toy
Karts
Wood
Table
1
Toy
Karts
Carpet
1
Teacher
Carpet
5
Weight of
the book
and plus
medium
(kg)
Force
(N)
Coeff
Work
of
(N-m) Static
Friction
Time
(sec)
Power
(Watts)
Safety Issues
When the instructor is being pushed along the track it is possible that he could fall. Make sure to
completely clear the area of any items.
Troubleshooting Tips
Make sure all the students are using the correct units especially when using the spring scale.
This will make the calculations a lot easier.
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Assessment
Pre-Activity Assessment
Title: Class discussion
Before starting the activity ask the students why they think cars use round tires to move and
whey the tires are made out of rubber? Ask the students the definition of friction.
Activity Embedded Assessment
Title: Filling out the table
During the activity students will have to record their values for weight, force, and time on the
table provided. From these values the students will have to calculate work, power and the
coefficient of static friction. The completion of the table will give the teacher a gauge on the
level of progress and understanding.
Post-Activity Assessment
Title: Homework assignment
Ask the students to write short answers for the questions that were asked during the class
discussion. In addition ask the students why the wheels made it easier for the object to move.
What two things will give you a higher coefficient of static friction? (weight and roughness)
Based on the work and power calculations which medium was the best to move the book?
References
Owner
Drexel University GK-12 Program
Contributors
Mr Manuel Figueroa, PhD Candidate, School of Biomedical Engineering, Drexel University
Ms Evelyn Cruz, Robotics Technology Teacher, Roberto Clemente Middle School, School
District of Philadelphia
Copyright
Copyright 2008 Drexel University GK-12 Program. Reproduction permission is granted for nonprofit educational use.
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