Finger Breaking Fun
General Overview:
Problem Statement: The goal of this experiment is to engineer and create a RudeGoldberg machine that will displace a mass of 1 kg, 1 meter high within, or as close to,
10 seconds. The materials used for building the machine must cost less than or equal to
$20. Each part of the machine may equal 2.5 kilograms or less.
Problem Solution: Our solution to this project was to build a machine that was a meter
wide and half a meter high, and to use the spring potential energy of rat traps to move the
kilogram weight. Our design included 5 rat traps, 5 pulleys, heavy rope with the least
amount of friction as possible, wood for ramps, backboard, and supports, and marbles.
The design consisted of rolling a marble (or a few marbles just to make sure) down 4
ramps setting off 5 rat traps in sequence. The rat traps would be connected with a rope
from the top rat trap, all the way to the bottom trap, plus the distance to a high pulley
down to the kilogram weight. As the first rat trap was set off, it would pull the string
close to 7 inches (the length of the trap). The rest of the string would tighten pulling the
kilogram weight up 7 inches also. As the marbles rolled down the ramps, they would
eventually set off four other traps measuring about 35 inches in all. Thus, the kilogram
weight would be pulled approximately a meter off the ground.
Cost of Machine:
Materials:
5 Pulleys
5 Rat Traps
Hooks, Screws, Nails, etc.
Wood
Bouncy Ball
Cost of Materials:
$15.87
Energy Conversions:
The process of energy conversion in our machine was mostly uniform. The initial
conversion was technically the same conversion for each trap set off. We suspended a
marble above the first rat trap giving the marble gravitational potential energy. We also
set all of the rat traps giving them potential spring energy. As we dropped the marble
from the initial height, potential energy was converted to kinetic energy as the marble
struck the trap. The trap was then set off converting all of the stored potential spring
energy into kinetic energy, resulting in tightening of the string and lifting of the kilogram
weight. The marbles continued to roll down a wooden ramp with a certain slope to keep
momentum going and repeated the process of the initial energy conversion (Gravitational
potential energy, to kinetic energy, to stored potential spring energy, to kinetic energy).
This process is repeated four times in order to pull the kilogram weight up one meter
giving the weight a greater potential energy.
→
Gravitational Potential Energy
Kinetic Energy
Theoretical Speeds
Equation Used: mgh = (½) mv²
Masses cancel, leaving: gh = (½) v²
Solving for Velocity:
v = 2 gh
Stage 1
V = 2(32.2
ft
1 ft
)(2.212in)(
)
2
12in
sec
= 3.45
ft
sec
V = 2(32.2
ft
1 ft
)(2.49in)(
)
2
12in
sec
= 3.66
ft
sec
Stage 2
Stage 3
V=
2(32.2
ft
1 ft
)(.868in)(
)
2
12in
sec
= 2.16
ft
sec
V=
2(32.2
ft
1 ft
)(.45in)(
)
2
12in
sec
= 1.55
ft
sec
Stage 4
Assumptions:
1.) No friction between ball and wood
2.) All kinetic energy lost after falling on trap
→
Potential Elastic Energy of springs
Work
Equation used: Elastic Potential Energy = F * D
Elastic Potential Energy = (1kg * 9.81
m
)(.178m)
sec 2
Elastic Potential Energy of each rat trap = 1.75 Joules
Conflicts
1. The strength of the springs would wear down over continuous testing. By the end,
there was not enough tension stored in the spring to lift the kilogram weight.
2. The string routing through each level and rat trap would create a massive amount of
friction that the springs would have to overcome before lifting the weight. Even with low
friction pulleys between each level, there was still an excessive amount of friction at the
points of attachment to the traps.
3. The grade of the ramps for the marbles to roll down was not steep enough to contradict
the friction forces of the wood and the obstructions found on the rat traps. The marbles
would often stop on the track or on the mouse trap itself. This would lead to the
remaining traps not being set off.
Conclusion:
In conclusion, we found out that our design wouldn’t work. Our design concept
was good, however we didn’t account for points of friction. The top rat trap had the
kilogram mass, plus eight different points of friction acting against the spring