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The Physics and Physiology of Collisions and Concussions

Text graphic for collisions and concussions.

Every school year, right around the time football and soccer are in full swing, our educational specialists field questions from educators about lessons centered around concussions. Since academics and athletics are often two key student interests, building lessons around sports is a great way to spark student curiosity and bridge scientific concepts with their lives outside the classroom.

We brought John Melville, our Director of Biology, and Fran Poodry, our Director of Physics, together to help answer some key questions about the relationship between collisions and concussions. We have also gathered several helpful resources for further research and a few ideas to bring into your classroom or laboratory.

The Physiology of Concussions

The skull is a protective casing around the brain that protects the brain from injury, but the brain itself is soft and is bathed in fluid. Forces that are applied to the skull—even mere shaking of the head—can produce an injury. Rapid acceleration or deceleration of the skull can cause the brain to actually hit the skull, which results in damaged brain tissue.

For a long time, it was widely accepted that a concussion produced a series of classic symptoms. These usually involved brief loss of consciousness, feelings of dizziness, and short-term memory problems. If you played contact sports in the last century, it was common to hear that you might “see stars”after you got your “bell rung,” which meant you had experienced a mild concussion.

More recently, the symptoms of concussions and other brain traumas have expanded to include more severe symptoms. During the Afghan War, a great number of veterans came back with changes in mood, behavior, and memory loss. We now know that these changes in behavior are related to traumatic brain injuries that were caused by the concussive force from explosive devices. There is a good deal of evidence that repeated concussions over time lead to a brain disorder called Chronic Traumatic Encephalopathy (CTE). Over the past decade, several high-profile boxers and NFL players have been diagnosed with CTE.

For further research, please check out Mayo Clinic’s and the CDC’s information on concussions.

The Physics of Collisions

A collision is when objects that were not previously in contact with one another move into contact. When objects come into contact, the interaction changes their velocities. When velocity changes, we call that acceleration. In the case of a collision where two objects meet and come to a stop, both objects undergo a change in velocity from their pre-collision velocity down to zero. If an object bounces back off something it collides with, its velocity may be reversed, which is an even larger change in velocity.

Concussion-causing collisions are a great topic to bring together Newton’s three laws of motion. Both objects in the collision experience the same amount of force (Newton’s third law), but because of the different masses involved, the accelerations are different (Newton’s second law). An insect colliding with the windshield of a moving car will experience a fatal acceleration, while the car’s slowing due to the collision is unnoticeable due to the difference in masses. Finally, the brain in its fluid inside the skull keeps moving with the rest of the body’s velocity (Newton’s first law) until it hits the inside of the skull.

In general, very brief (think milliseconds) collisions have higher accelerations and drawn-out (tenths of a second) collisions have smaller accelerations. Coming to a stop from a high speed results in a greater acceleration than coming to a stop from a slow speed, if both collisions happen in the same amount of time. Measuring accelerations using a sensor can be a good way to investigate collisions that can lead to concussions.

Measuring Collisions

The SI units for acceleration are m/s2, but many people like to measure acceleration in multiples of the acceleration of an object in freefall near Earth’s surface, known as g. The value of g is 9.8 m/s2. The Go Direct® Acceleration Sensor can be set to measure in terms of g, or in units of m/s2 or N/kg.

Bringing Collisions and Concussions into the Classroom

Here are a few ideas to help you build hands-on investigations to help your students understand the physics of collisions and concussions.

Classroom Idea 1

First, our partners at Pivot Interactives have an activity in which students measure the compression of different types of foam padding and the acceleration of a heavy mass as it comes to a stop against the foam. Students can choose to analyze different foam types, foam densities, and collision speeds from a collection of high quality videos.

Check Out The Video and Get a Free Trial to Pivot

Classroom Idea 2

Recent medical literature suggests that concussions may occur when brain tissue experiences accelerations in helmeted impacts upward of 66 g (25% probability of moderate traumatic brain injury, or mTBI.) Concussions are also more likely the higher the acceleration. Task your students with an experiment that challenges them to use an empty helmet or a soccer ball and Go Direct Acceleration to design a method to measure the accelerations that happen on the field. Once they can measure accelerations, they can investigate ways to minimize accelerations during collisions.

Helpful Experiment Prep Tips

  • In order to set up such an experiment, we recommend switching the sensor channels from the default X-axis acceleration channel to the X-axis acceleration-high channel, which measures in the range of ±200 g.
  • If the object you are testing may twist or turn during the experiment, we recommend using all three of the high acceleration channels.
  • Use the mode settings to increase the sampling rate of the sensor to 1000 samples per second, as high accelerations can happen over very short periods of time. Note that with 3 channels collecting data at 1000 samples per second, the app response may slow down. The sensor data collection will not be affected, but the data may take a minute to appear on your app screen.
  • If you activated the X-, Y-, and Z-axis acceleration-high channels, you will need to determine the total magnitude of the acceleration. Create a new calculated column and apply the magnitude formula (the magnitude of a vector is the square root of the sum of the squares of the perpendicular components of that vector). Use the three acceleration columns as X, Y, and Z in the expression. Graph the magnitude of the acceleration vs. time.

    Here is the formula you select for the calculated column:

    Graphical Analysis 4 screenshot of calculated column formula

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