The objective of this project was to create a structure that will protect a raw egg and prevent it from breaking when being dropped from a minimum height of two meters. A decent hypothesis or prediction one could develop before any experimental trials would be as follows. The structure that provides the longest duration of impact between the falling egg the ground will provide the desired results of an undamaged egg. The duration of time in which the ground applies a force to the egg carrying structure is referred to as impulse. The longer the span of impact time, the more mild the force acting upon the egg.
For this challenge the students were limited to fifty drinking straws, two post-it notes, one raw egg, and a meter of tape. In the previously stated hypothesis, impulse was the deciding factor in what will prevent the egg from breaking. The force normally applied to the egg by the ground when being dropped from the introductory height of two meters would be far too great causing the egg to break. Therefore, lab participants needed to find a way to either elongate the duration of the impact, or find a way to slow down the egg’s normal final velocity when it strikes the ground. Velocity is described as, “the displacement divided by the time interval during which the displacement occurred” (Serway & Faughn, 2002, p. 43).
Prior to the trials at the set heights, there seemed to be multiple structural designs that would suffice as an egg protecting or slowing agent. However, with a little bit of thought regarding the materials provided, one could deduce that a structure that would slow the time of impact between the egg/structure and the ground would be the most successful from the three different drop heights of two, three, and five meters. One design that would generate success would be a system of shapes that would act as a spring system that would cushion the egg’s fall. A spring system would cause the structure to contract upon impact, which would take a lot longer than a bare egg’s impact with the ground. This is why a spring system would instantly come to mind when your goal is to elongate impact time.
There were also many other factors that had to be considered as the height of the drop increased causing the final velocity of the egg to increase as well. For one, the egg could potentially pop out upon the structure’s impact with the ground. This could easily be prevented by taping the egg to the straws, but one of the guidelines outlawed this, only allowing the egg to be held to the structure by mechanical means only. A solution to this problem would be to build around an egg in the first place. If you knew the exact dimensions of the type of egg that was being used in the drop, you could connect the straws in such a way that they would create an air tight seal around the egg used in the lab which is the next best thing other than taping the egg to your structure.
Another factor that the builder must consider was the contraption falling the intended way. After all, as the heights increase, it becomes harder to accurately predict the way in with the structure will twist and turn in the air. As a builder, you could create a more consistent impact by building a symmetrical structure that would function the same upon impact when being dropped in any manner. One suggestion would be to stray from building a system of legs that were only on the bottom, making the only safe landing right-side up. Therefore, upon considering all of those factors and potential flaws, the best design you could come up with prior to any experiments would be a symmetrical spring like structure with an airtight compartment for the egg would be ideal for the task at hand.
Given that air resistance is negligible, gravity will equal 9.81 meters per second squared. Using a series of kinematic equations, the speed of the egg upon impact with the ground can be determined for all three heights of two, three, and five meters. Since the egg was dropped from rest, the initial velocity would be zero. Using the equation, final velocity squared equals initial velocity squared plus two times acceleration times delta distance, the final speed can be determined for each of the varying heights from the different trials.
The speeds of impact from the heights of two, three, and five meters are as follows, 6.26meters per second from a height of two meters, 7.67meters per second from the height of three meters, and 9.91meters per second from the height of five meters.
Only one design survived from the height of five meters. This design was symmetrical and possessed an air tight egg compartment, which fit the previously mentioned successful qualities. All the failing designs possessed at least one of the mentioned flaws.
After viewing the trials of drops, multiple flaws were highlighted in many designs of the lab participants. One flaw that could have been improved on was more even distribution of straws surrounding the egg compartment, rather than overbuilding on one side. This could be solved by building symmetrically. Another noticeable flaw was the reckless flight patterns of designs that were intended to fall a certain way. This also had the easy fix of just building symmetrically and not caring about the way it hit the ground.
The force exerted by the egg onto the straw structure was something that seemed to be forgotten in some of the designs. Assuming that the eggs used had the mass of .0567kilograms, which is the minimum mass of an egg of the type used, the egg would certainly have an impact on your straw structure would barely have a larger mass in most cases. The amount of impact can be calculated by using the eggs mass and the previously calculated velocity from a certain height to determine the amount of energy lost to sound, since the collision can be considered perfectly inelastic. A perfectly inelastic collision is defined as, “when two objects collides and move together as one mass” (Serway & Faughn, 2002, p. 222).
The structure and the egg’s collision can be considered inelastic only if the egg is trapped in its compartment without movement. The amount of sound can be measured during the impact telling you how much energy is lost in the collision, telling you the impact the egg had on the structure. This impact can also be determined by observing and measuring the way the straws flex upon impact with the ground with and without the egg and comparing. The egg protecting structures can be directly compared with today’s car bumpers.
Similar to the egg protecting structure, the goal of a bumper is to make the time interval in which the impact of the collision is taking place as longs as possible to reduce the jarring that the passenger experiences. A car bumper is pretty flimsy for the most part as well as hollow, with nothing between the surface of the bumper and the front of the car other than air and a small amount of metal or plastic. The modern bumper is made to crush down completely with very little applied force at all. Below is a picture of a semi successful egg protection structure.
Courtney from Study Moose
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