Download Conservation of Energy

Presented by: Michael A Sierra, Jimmy Hernandez
SC 441, Spring 2001, Professor Roman Kezerashvili
Fgrav = m * g
OBJECTIVES
Determination of the kinetic and gravitational and potential
energy of a body and an experimental test of the principle of
conservation of mechanical energy in the gravitational field of the
earth.
Equipment
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Air track system with one glider.
Science Workshop interface box.
Two photogate accessories.
Meter stick.
Vernier caliper.
Set of masses: 50 g and 100 g.
Two blocks of cylinders.
Theory
There are two kinds of mechanical energy. The energy that an object possesses by virtue of its
position, and is defined as potential energy. The gravitational potential energy is the energy that an
object of mass m has by virtue of its position above the surface of the earth.

In addition to having energy by virtue of its position, an object also possesses energy by virtue of
its motion. The energy that an object possesses by virtue of its motion is the kinetic energy.
The sum of these two kinds of energy are called the total mechanical energy E.
E = U + K.

In an isolated system, the total energy of the system remains a constant . This is the law (principle) of
conservation of energy. In other words the principle of conservation of energy state that total mechanical
energy remains a constant along all the path between the initial and final points, never varying from the initial value.

The tendency of an object to conserve its mechanical energy is observed whenever external forces
are not doing work. If the influence of friction and air resistance can be ignored (or assumed to be
negligible) and all other external forces are absent or merely not doing work, then the object is often said
to conserve its energy. “If only internal forces are doing work (no work done by external forces), there is
no change in total mechanical energy; the total mechanical energy is said to be ‘conserved.’ ”
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Kinnetic energy gain, ∆K =
((mv22)/2) - ((mv21)/2)
Loss in potential -∆U = -(mgy2 mgy1), J
% difference
0.150
0.133
12.45
0.179
0.155
14.71
0.204
0.177
14.15
0.098
0.088
9.92
0.115
0.103
11.02
0.131
0.118
10.71
Table 2. Data and Results of Calculations
Mass of Glider: .3Kg
Height y1: .14m /
.125m
Length of Flag: .03m
Height y2: .095m
Position 1
Mass
m,
Kg
Potential
energy
U1 =
mgy1, J
Position 2
Total
energ
y E1 =
K1 +
U1, J
Velocit
y
V2
,
m/
s
Kinetic
ene
rgy
k2 =
mv2
2) /
2
Potentia
l
ene
rgy
E2
=
K2
+
U2,
J
Total
ene
rgy
E2
=
K2
+
U2,
J
%
Diff
ere
nce
Velocity
V1, m/s
Kinetic energy
k1
=(mv21)/2
0.301
0.485
0.035
0.412
0.448
1.111
0.185
0.280
0.465
3.85
0.351
0.482
0.041
0.481
0.522
1.120
0.220
0.326
0.546
4.60
0.401
0.481
0.046
0.549
0.596
1.117
0.250
0.373
0.623
4.42
0.301
0.394
0.023
0.368
0.391
0.897
0.121
0.280
0.401
2.33
0.351
0.394
0.027
0.429
0.457
0.901
0.142
0.326
0.469
2.60
0.401
0.392
0.031
0.491
0.521
0.899
0.162
0.373
0.535
2.52
Questions
• Was the mechanical energy of the glider in motion conserved? Discuss the
possible sources of error
A/ Friction force from air
Small friction force from air track system
• A glider released from a starting height at an inclined air track bounces to
one-half its original height. Discuss the energy transformations that take
place.
A/ In any isolated system, the total energy of the system remains constant
along the paths between the initial and final points. Potential energy
transforms to the kinetic energy of the glider and partially into internal
energy of the glider (Heat energy ).
In its simplest form, the ollie is a jumping technique that allows skaters to hop over
obstacles and onto curbs, etc. What's so amazing about the ollie is the way the
skateboard seems to stick to the skater's feet in midair. Seeing pictures of skaters
performing soaring 4-foot ollies, many people assume that the board is somehow
attached to the skater's feet. It's not. What's even more amazing about the ollie is
that to get the skateboard to jump up, the skater pushes down on the board! The
secret to this paradoxical maneuver is rotation around multiple axes. Let's take a
closer look.
Why are roller coaster loops made into egg-shaped ovals rather than circles?
First, start with the fact that the ride begins by lifting the cars to a large height,
then allowing gravity to power the rest of the ride. We can use conservation of
energy and and knowledge of circular motion to predict what would happen for
a circular loop as depicted below
• We have proved the principle of conservation of mechanical energy,
by calculating the gravitational potential energy which was found to
be the same through out the experiment. The potential energy lost
was equal to the kinetic energy gained. The total energy of the
system was conserved.
• One can use the transformation of energy in many cases, for
example a ski jumper glides down the hill towards the jump ramp
and off the jump ramp towards the ground. Potential energy is
transformed into kinetic energy. Of course, it should be noted that
the original assumption that was made for the ski jumper is that
there were no external forces doing work. In actuality, there are
external forces doing work.