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Physics 4AL
Lab for Science and Engineering Mechanics
Experiment 3:
Conservation of Mechanical Energy
Lab Section:
LAB 5
Name:
SunYi Lim
UID:
503576474
Date:
7/13/10
TA:
Chris Tyndall
Partner:
Jaimie Yap
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The law of energy conservation states that total amount of energy in a system stays constant over time.
=
+
Total E KE PE
Where KE is the kinetic energy (
12kx2
)
and PE is the potential energy (
12mv2
).
‘
k
’ being the spring constant,
‘
x
’ being the distance of displacement, ‘m’ is the mass, in this experiment, it will be the combination of the mass of
the glider and spring, and ‘v’ is the velocity of the glider.
In this experiment, we are to observe the law of conservation of mechanical energy with a simple
experiment with a glider on an air track attached with “measuring comb”, two springs, and five sets of weights. To
minimize the complications in the calculations, the experiment is conducted on the air track to minimize the friction
factor. Two springs are attached to the ends of the comb to the ends of the air track, and the measuring comb is
attached directly above the glider for measuring purposes. To calculate the energy in the system, we need to apply
Hooke’s law to find the spring constant. The Hooke’s law states that:
=
F
kx
Where
F
is the force exerted in by an object or person. Using known mass, the weight is attached at the one end of
the glider, and the displacement distance is measured. By plotting and analyzing the data, we should be able to see if
there is any friction affecting the system.
Before calculating the total energy in the system, the spring constant needs to be determined. When there is
no weight attached, the glider comes to equilibrium. This position will be set as x = 0. Once a weight is attached at
the end of the string, the glide arrives to a new equilibrium. At this point, the spring force balances the gravitational
force and the total force is:
=


=
F Mg kx x0 0
Where
M
in this case is the mass of the hanging weight,
g
is the gravitational acceleration constant, 9.81 m/s^2,
k
is
the spring constant that we are trying to measure,
x0
is the position that the glider sits at when there is no weight,
and the
x
is the glider’s new position once the weight is added. To find
k
, hang different weights,
M
, and record the
x
. Let
y = Mg
for each weights, and graph a displacement vs. force graph. In addition, add trendline (
y = kx + b
) to
determine the
k
value for this specific system.
When the glider is pulled back from its equilibrium position, the system gains potential energy of:
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