SIMPLE MACHINES, WHEEL & AXLE
RST-LAB-003 Rev B
A)
OBJECTIVE
To determine experimentally and mathematically the MECHANICAL ADVANTAGE of a wheel & axle system and to introduce the
concept of TORQUE.
B)
BACKGROUND
The screwdriver is a type of SIMPLE MACHINE called a Wheel & Axle. A SIMPLE MACHINE is a device that performs work by
converting forces and distances. The screwdriver is used to create TORQUE, a rotational or twisting force that can be measured by
multiplying Force times Distance. All simple machines have a characteristic called the MECHANICAL ADVANTAGE (MA). The
MECHANICAL ADVANTAGE can be obtained experimentally by building a Wheel & Axle and using the formula:
MECHANCIAL ADVANTAGE= MA = Distance moved by the wheel / Distance moved by the axle
The MECHANICAL ADVANTAGE can also be calculated mathematically by using the formula:
MECHANCIAL ADVANTAGE = MA = Diameter of the Wheel / Diameter of the Axle
In this lab, you build a Wheel & Axle, determine the MA experimentally and mathematically and compare results.
C)
PROCEDURE
PART 1: EXPERIMENTAL METHOD
1. Build the Screwdriver per instructions.
2. Attach one string weighted with washers to the Wheel (handle) of the screwdriver and another weight string to the Axle (shaft)
as shown in Figure 1.
3. Hold the screwdriver so the weights hang straight down. Measure the length of each string and record in the “0 TURNS” box in
D) DATA Part 1.
SHEET 1
Copyright © 2014 RST. All Rights Reserved.
SIMPLE MACHINES, WHEEL & AXLE
RST-LAB-003 Rev B
4. Turn the screwdriver exactly 1 (one) turn. Measure the length of each string and subtract from the “0 TURNS” measurement to
determine how much string was wrapped around the Wheel (handle) and Axle (shaft). This value is the DISTANCE the Wheel
and Axle have traveled. Record these values in the “1 TURN” box in D) DATA Part 1.
5. Turn the screwdriver another turn making sure the string does not overlap. Repeat the measurements for the length of each
string and record in the “2 TURNS” box in D) DATA Part 1.
6. Repeat Step 5 for 3 and 4 turns.
SHEET 2
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SIMPLE MACHINES, WHEEL & AXLE
RST-LAB-003 Rev B
PART 2: MATHEMATICAL METHOD
1. Obtain several specimens of screwdrivers. NOTE: Use care when handling.
2. Using calipers, measure the diameter of the handle (wheel), axle (shaft) and length of the shaft. Record in D) DATA Part 2
D) DATA
PART 1: EXPERIMENTAL METHOD
NUMBER OF TURNS
STRING LENGTH (cm)
WHEEL (HANDLE)
AXLE
0
1
2
3
4
TOTAL MOVEMENT
SHEET 3
Copyright © 2014 RST. All Rights Reserved.
SIMPLE MACHINES, WHEEL & AXLE
RST-LAB-003 Rev B
SIMPLE MACHINES, WHEEL & AXLE
PART 2: MATHEMATICAL
METHOD
RST-LAB-003
Rev B
SPECIMEN
(A) DIAMETER
WHEEL
(B) DIAMETER
MECHANICAL ADVANTAGE
(A / B)
AXLE
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SIMPLE MACHINES, WHEEL & AXLE
RST-LAB-003 Rev B
E) CALCULATIONS
PART 1: EXPERIMENTAL METHOD
Determine the MECHANICAL ADVANTAGE by using:
MA = Distance moved by the wheel / distance moved by the axle
PART 2: MATHEMATICAL METHOD
Determine the MECHANICAL ADVANTAGE by using:
MA = Diameter of the Wheel / Diameter of the Axle
F)
QUESTIONS
1)
2)
3)
4)
5)
G)
How did the results of the two methods of calculating the MA compare?
Which weight moved up the fastest? Why?
What does a screwdriver do for us?
What effect does the length of the shaft have on the MA of a screwdriver?
How could you increase the MA of a screwdriver?
DESIGN CHALLENGE
Design a screwdriver that is capable of creating 25 Nm of torque with 5 Nm torque as input
SHEET 5
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SIMPLE MACHINES, WHEEL & AXLE
RST-LAB-003 Rev B
H)
GLOSSARY
MECHANICAL ADVANTAGE: The factor by which a SIMPLE MACHINE converts Forces and Distances
SIMPLE MACHINE: A device that converts Forces and Distances
TORQUE: A rotational, or “twisting” force. For example, te amount of force needed to remove a lid off a jar. Torque is
measured by force multiplied by distance. For example, a foot pound is one pound of force at a distance of one foot (1 ft
lb) or one Newton of force at a distance of one meter (1 Nm). Refer to the Torque Wrench demo.
I)
UNDERSTANDING
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Wheel and Axles are SIMPLE MACHINES; devices that convert forces and distances and in doing so, make tasks easier.
The ratio of the difference in the distance (circumference) of the Wheel (handle) and Axle (shaft) is the Mechanical Advantage
(MA) of the system.
As in all simple machines, forces and distances are converted (traded). The screwdriver “trades” the longer distance traveled by the
handle (bigger circumference) for the greater force applied to the axle (shaft).
The MECHANICAL ADVANTAGE can also be calculated by the ratio of the diameter of the handle (wheel) to the shaft (axle).
The screwdriver is used to create TORQUE, a rotational or twisting force that can be measured by multiplying Force times Distance.
SHEET 6
Copyright © 2014 RST. All Rights Reserved.