The Second Law of Motion
Theory
:
The Second Law of Motion states that:
“The acceleration of an object is directly proportional to the net
force applied to the object and inversely proportional to the
mass of the object.”
If the acceleration is in units of meters/sec
2
, the mass is in units of kilograms, and
the force is in units of Newton’s, then the second law of motion is expressed by
the equation
F
= m
a
[1]
In equation [1],
F
is the
net
applied force, m is the mass of the object on which
the force is applied, and
a
is the acceleration of the object in response to the force.
In this experiment, a force will be applied to a cart of mass m
1
(mass of cart plus
the added mass), by hanging weights on a string which is attached over an almost
frictionless pulley to the cart, as sketched in Figure 2  1.
There is however, some friction between the cart and the track.
Let F
f
be the
force of friction
which opposes the motion of the cart.
The hanging weight
W
2
is
opposed by the force of friction on the cart,
F
f
.
Recall that the weight,
W
2
, is related to the mass, m
2
, by the equation
W
2
= m
2
*
g
,
[2]
Leveling Knob
Stop
m
1
m
2
smart
pulley
Figure 2  1
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
where
g
is the acceleration due to gravity (about 9.8 m/s
2
).
The net force, which
accelerates
both the cart and the hanging mass
(i.e., the
total mass of the
system
), is then
F
= (
W
2

F
f
),
Hence, equation 1 may be rewritten as
W
2

F
f
= m
a
[3]
W
2
= m
a
+
F
f
[4]
where m is the total mass of the system, i.e. m = m
1
+ m
2
.
Notice that Equation
[4] is of the form of a straight line, y = kx + b, provided the total mass (m
1
+ m
2
)
is constant as W
2
is varied.
Thus, theory predicts that if the hanging weight is
plotted as a function of the acceleration of the system, a straight line should result.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 Staff
 Physics, Acceleration, Force, Mass, Second Law Of Motion, partner

Click to edit the document details