Is Your Helmet Knockin’ Your Noggin? Oobleck it!

Abstract:

In this experiment, the objective is to prove with experiments and data the unique non-Newtonian property of Oobleck can reduce the impact force registered inside of a helmet. Registering the force inside the helmet is important because that is where the brain is.

A few prompt questions are considered:

  • Can we make better sports helmets to prevent concussions?

  • Why did football helmets change from leather (soft) to plastic (hard)?

  • What material will provide both soft-hard properties?

  • How to prove the protection effectiveness by experiments?

The experiment includes using a wireless accelerometer paired with a Smartphone App set at the highest sampling rate (50Hz) for data collection and then exporting data and graphs to Google Classroom for analysis. Numerous runs have to be performed in order to eliminate human error, sampling limitation and insure consistent results. We find that helmets with Oobleck experience about half the impact force with more protection effectiveness compared with Oobleck-less helmets.

Background:

“In 2016, 18,477 cyclists were injured including, 3,499 who were killed or severely injured”1

                      “1 in 5 high school athletes will sustain a sports concussion during the season” 2

A bicycle helmet is chosen for this study. A bike helmet is an item of protective gear, designed to attenuate impact to the head when a cyclist falls or has a collision. The conventional helmet has two principal protective components: a thin, hard, outer shell typically made from polycarbonate plastic or fiberglass and a soft, thick, inner liner usually made of expanded polystyrene or polypropylene "EPS" foam that is supposed to absorb and minimize force impact.

Regarding the historical aspect of helmets, football helmets used to be made out of soft leather.3 Athletes switched to a harder, plastic helmet when there was a demand for more protection to reduce the cracked skulls. However, while there are fewer cracked skulls, the incidents of concussions have increased. The effects of concussions are long-term and may be debilitating years after a sports career has ended.

Discussion:

The main problem that needs to be resolved when designing a helmet is how can we decrease the force affecting the person wearing it. Using physics and the formula FΔt=mΔv, we understand that by increasing the contact time we decrease the overall magnitude of force.

Looking back at the helmet structure we see a problem - the hard outer shell.  A hard shell is not efficient in absorbing the impact because the contact time is short. A large impact force occurs as a result. The soft inner liner then does not absorb the force fast enough to make most helmets not as efficient to protect the brain.

Hypotheses:

In order to achieve that most protection by increasing the contact time, we must place another layer of the material that will increase that contact time over the outer hard shell. Think about crumple zones on cars. During a collision, the crumple zone deforms, increasing the contact time and absorbing the energy of collision. Without the crumple zone, passengers would feel the full impact force. We are basically looking for a material (Oobleck) that can act like the crumple zone on a car.

Oobleck rational:

Oobleck, a non-Newtonian fluid,4 was picked because of its unique properties. A non-Newtonian fluid is a fluid whose viscosity varies based on the applied force so when struck with a sufficient force it instantly changes from a liquid to a solid. This sudden change in Oobleck should increase the contact time and lessen the impact and, therefore,  lessen damage to the brain. In addition, the phase change from liquid to solid will absorb some of the energy from the impact just like a car’s crumple zone.

Materials:

Bike Helmet, Wireless PocketLab Accelerometer, Smart phone, PocketLab App

Velcro, Ruler, Oobleck* (prepared by mixing cornstarch and water in 2 to 1 ration)

* Oobleck gets its name from a Dr. Seuss book, Bartholomew and the Oobleck, in which Bartholomew must rescue his kingdom from a sticky green substance called Oobleck.

Procedures

  1. Fasten the Pocket Lab Accelerometer inside the helmet with the Pocket Lab App turned on at the highest sampling rate 50Hz.

  2. Drop the helmet at the control height of 1ft.

  3. Take slow-motion video during the drop. (attach video)

  4. Export the xyz acceleration data and graph to Google Classroom.

  5. Calculate total acceleration = (x2 + y2 + z2) ^ 0.5

  6. Review the slow-motion video to interpret the graphs.

  7. Repeat tests for the helmet until consistent results are obtained.

  8. Repeat tests for the helmet with Oobleck until consistent results are obtained.

Video

Data & Analysis

Conclusion:

In light of the many concussions reported each year, improvements are needed in helmet design. Helmets have to be both hard and soft elements. The hard outer shell protects against skull fractures but decreases the contact time compared with a soft (leather) shell, thereby increasing the chance of a concussion. Padding inside the helmet is supposed to cushion the impact but current padding clearly is not enough to protect athletes. An additional material on the hard outer shell of a helmet is needed. The results here indicate that Oobleck, a non-Newtonian fluid, is just such an effective material. The unique property of Oobleck provides both soft and hard collision protection. It is liquid before impact but quickly becomes solid upon impact. Unlike clay that remains deformed after a collision, Oobleck reverts back to a liquid and is ready to protect again.  Incorporating Oobleck on the outside of a helmet was shown here to decrease the force inside a helmet of a collision by increasing the impact contact time. Without Oobleck, the force measured 7.45 g. The contact time of about 0.02 seconds, with a change of speed of 2.44 m/s. However, the force inside a helmet with Oobleck was only 4.00 g, with a contact time of about 0.04 seconds for the same (2.44m/s) change of speed. The results, therefore, indicate that Oobleck improves the protection effectiveness to 67% compared with the 40% effectiveness of an Oobleck-less helmet.

In addition, the wireless accelerometer at 50Hz sampling rate is proven to give consistent results.

Credit

Oobleck suggested by Christopher Nuzzolo

Report contributed by Aiko Schinasi, Sofiya Lobanovich, Miranda McKeon, Emma Matthews,

Alexandra Savage Christopher Nuzzolo, Brooke M. Fortunato, Annabella DeAngelis, Jack Yannone, Nicholas Santangelo and Aidan Kunzle

Model created by Grace li Sayles

Data submitted by Isabella Guerrero, William Keeney, Conner Stevens, Amanda Plasse and Adam Bock

Work assigned to Dr. Labowsky’s Physics CP classes

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