Atwood’s Machine
Tiffany Kayla Taylor
Names:
ICP
Period:
Date:
12-12-12
A classic experiment in physics is the Atwood’s machine: Two masses on either side of a pulley
connected by a light string. When released, the heavier mass will accelerate
downward while the lighter one accelerates upward at the same rate. The
acceleration depends on the difference in the two masses as well as the total
mass.
In this lab, you will determine the relationship between the two factors which
influence the acceleration of an Atwood’s machine using a Photogate for
measuring acceleration.
40 cm
PRELIMINARY QUESTIONS
1. If two equal masses are suspended from either end of a string passing
over a light pulley (an Atwood’s machine), what do you expect to occur? Why?
The acceleration will be 0
2. For an Atwood’s machine, how would you expect the acceleration to change if you:
 Move mass from one side to the other, keeping the total mass constant?
One side being heavier then the other
 Gradually increase the mass of both sides?
The acceleration will be the same aslong as both sides are the same. The only way the
acceleration will change is if we have different weights on each side.
3. Why do the two masses have the same acceleration?
Because they do not move because they weight the same
Part 1 – Keeping Total Mass Constant
For this part of the experiment you will keep the total mass used constant, but move weights
from one side to the other. The difference in masses change.
1. Set up the Atwood’s machine apparatus as shown in Figure 1. Be sure the heavier mass can
move at least 40 cm before striking the floor.
2. Open the file “10 Atwood’s Machine” in the Physics with Vernier folder. A graph of velocity
vs. time will be displayed.
3. Arrange a collection of masses totaling 200 g on m2 and a 200 g mass on m1. What is the
acceleration of this combination? Record your values for mass and acceleration in the data
table. (note: You don’t really need to collect any data for this trial.)
4. Move 5 g from m1 to m2. Record the new masses in the data table.
5. Position m2 as high up as it can go. Click
to begin data
collection. Steady the masses so they are not swinging. Wait one
second and release the masses. Catch the falling mass before it
strikes the floor or the other mass strikes the pulley.
6. Autoscale and then select the region of the graph where the
velocity was increasing at a steady rate. Click the Linear Fit
button
to fit the line y = mt + b to the data. Record the slope,
which is the acceleration, in the data table.
7. Continue to move masses from m2 to m1 in 5 g increments, changing the difference between
the masses, but keeping the total constant. Repeat Steps 5 - 6 for each
Mass 1 Mass 2
mass combination. Repeat this step until you get data for the following
200 g
200 g
six combinations.
195 g
205 g
190 g
210 g
8. Complete the data table by filling in the remaining columns.
185 g
215 g
180 g
220 g
175 g
225 g
DATA TABLE
Part 1: Keeping Total Mass Constant
m1
m2
(g)
(g)
1
200
2
Trial
Acceleration
m
(mass difference)
mT
(total mass)
(m/s )
(g)
(g)
200
0
0
400
195
205
.2256
10
400
3
190
210
.4248
20
400
4
185
215
.6874
30
400
5
180
220
.9174
40
400
6
175
225
.9000
50
400
2
Part 2 – Keeping Mass Difference Constant
For this part of the experiment you will keep the difference in mass between the two sides of
the Atwood’s machine constant and increase the total mass.
1. Set up the Atwood’s machine apparatus as shown in Figure 1. Be sure the heavier mass can
move at least 40 cm before striking the floor.
2. Open the file “10 Atwood’s Machine” in the Physics with Vernier folder. A graph of velocity
vs. time will be displayed.
3. Put 100 g on m2 and 80 g on m1.
4. Position m2 as high up as it can go. Click
to begin data
collection. Steady the masses so they are not swinging. Wait
one second and release the masses. Catch the falling mass
before it strikes the floor or the other mass strikes the pulley.
5. Autoscale and then select the region of the graph where the
velocity was increasing at a steady rate. Click the Linear Fit
button
to fit the line y = mt + b to the data. Record the
slope, which is the acceleration, in the data table.
6. Add mass in 20 g increments to both sides, keeping a constant difference of
20 grams. Record the resulting mass for each combination in the data table.
Repeat Steps 5 - 6 for each mass combination. Repeat this step until you
get data for the following six combinations.
7. Complete the data table by filling in the remaining columns.
Mass 1
80 g
100 g
120 g
140 g
160 g
180 g
Part 2: Keeping The Mass Difference Constant
m1
m2
(g)
(g)
1
80
2
Trial
Acceleration
m
mT
(mass difference)
(total mass)
2
(m/s )
(g)
(g)
100
1.029
20
180
100
120
.8529
20
220
3
120
140
.7206
20
260
4
140
160
.5995
20
300
5
160
180
.5479
20
340
6
180
200
.4923
20
380
Mass 2
100g
120 g
140 g
160 g
180 g
200g
ANALYSIS
Site specific example of your data to explain what happens to the acceleration if you:
 Move mass from one side to the other, keeping the total mass constant?
The total mass is the same but the individual mass on each side changes which mean that the
net force will be pulling harder on the heaver side then the lighter side.
 Gradually increase the mass of both sides, keeping the difference constant?
The constant is always the same because the total mass is always the same we are just adding
to it.