Design a Better Football Helmet Lesson

Lesson Description:

Recently, the NFL and other sports agencies have focused on the issue of concussions. Players are often subjected to intense blows or collisions on the field of play, and the number of concussions resulting from inadequate head protection seems to be on the rise. This activity allows students to use inquiry to investigate the materials used to make sports helmets and to propose shell and cushioning material in “designing a better football helmet.” The lesson allows students to perform real scientific tests centered on a “real-world” problem. The students, in the inquiry portion of the lesson, perform impact tests on polymer samples by dropping a plumb bob from differing heights onto the samples. The tests, modeled after actual industrial testing methods, measures the toughness and brittleness of polymers that have been subjected to intense blows. Both rigidpolymer materials that may be used in the outer shell of a helmet and foamed plastics that can be used for the inner lining of the helmet are tested in the lab, and, upon lab completion, students have to put forward their recommendation of a combination of shell and lining material that might be used to create a helmet capable of protecting players better than other combinations.

Objectives:

What should the students know as a result of this lesson?

Students will….

•know the importance of safety gear (helmets) used in sports.

•explain the purpose of an impact test.

•explain that impact resistance describes how a material reacts to shock or sudden stress.

•identify the functions of the hard outer shell and the foamed inner lining of a sports helmet.

•distinguish between the structure of a helmet made for multiple collisions, such as a football helmet, and a helmet made for a single collision, such as a bike helmet.

What should the students be able to do as a result of this lesson?

Students will….

•test the ability of various polymers to resist impact (sudden blows).

•compute impact in inch-pounds or Newton-meters.

•work cooperatively.

•perform tests on materials designed to mimic actual industrial tests and collect data.

•examine and analyze data collected from the testing of polymers to determine which plastics would be most suitable for use in a helmet.

Materials Needed:

Note: We obtained our impact testing kit (all materials required for this lesson) from Educational Innovations, Inc.; 888-912-7474

  • A video clip or picture showing a football tackle or a PowerPoint or Keynote file with multimedia images and/or videos with lesson description outlined step-by-step.
  • Samples of a variety of hard plastics – cut nearly the same size - each sample labeled with the correct name.
  • Clear tube or stiff cardboard tube from a wrapping paper roll with a viewing slit cut in the side. Tube should be at least 30 inches long. Use a magic marker to mark off the tube at 6 inch intervals.
  • Plumb bob or other standard weight to be used as a dropping object.
  • String - at least 36 inches long
  • Piece of wood to set under the test area.
  • Square block
  • Safety goggles
  • Ruler or meter stick
  • Ring stand and clamp – optional 1 1/2” dia.
  • PVC coupling or small diameter jar lid
  • Lab Procedures (developed with students during discussion)

Lesson Plan (5-E model):

Engagement:

Show a short video clip, a series of clips, or a series of images using Keynote or PowerPoint of football tackles and hits in the NFL and college games in order to catch students’ attention and allow the presenter to present the lesson focus.

Interact with students to discuss the tremendous forces that athletes are asked to endure on the field of play. Have students discuss minimum protective equipment, and have them focus on the importance of having adequate protection in the helmet. The historical advancement of the helmet from leather covering to its current incarnation might be prudent as well.

To make the initial discussion more interesting the following background information should be discussed:

In sports, body armor is designed to protect the participant from projectiles (mainly balls), from human impact, and from crashes. Many sports, such as football, cycling, and baseball require athletes to wear helmets. The outer shell of the helmet must be impact resistant while the interior must mitigate an impact by slowing the deceleration of the head.

The National Operating Committee on Standards for Athletic Equipment (NOCSAE) has developed voluntary test standards designed to reduce head injuries by establishing requirement of impact attenuation for football helmets/face masks, baseball/softball batting helmets, baseballs and softballs, and lacrosse helmets/face masks. The various regulatory bodies for sports, including the NCAA and the National Federation of State High School Associations have adopted these standards.

In football, on the field concussions are considered one of the most serious of contact sports injuries. Concussions are most likely to happen as the result of a blow to the side of the head, rather than the front or top, according to new research conducted by Biokinetics & Associates. Football is responsible for approximately 100,000 concussions in the United States each year.

The NOCSAE test standard for football helmets involves mounting a helmet on a synthetic head model and dropping it a total of 16 times onto a firm rubber pad from a height of 60 inches. Drops are made onto 6 locations on the helmet. Most of the drops are conducted at ambient temperatures, however, at least 2 of the drops are conducted immediately after the exposure of the helmet to 120° F for four hours. The equivalent of a 60-inch drop test would occur if a player running at 17.9 ft/sec (12.2 mph) ran into a flat surface which stopped his head in less than one inch. Most players run faster than this (average speed of a player running 40 yards in 4.8 seconds is 25 ft/sec) but vary rarely would the head be stopped in such a short distance on the football field.

In baseball and softball, the primary hazard is being struck by a pitched or batted ball. Therefore, baseball helmets are mounted on an instrumented headform that is free to move. An air cannon is used to shoot a baseball from close range into the helmeted headform at 60 mph. Impact accelerations are measured and a Severity index is calculated.

Evaluation for Engagement Activity:

Assessment is informal at this stage. Try to involve all students in the discussion. Allow students to cite examples from their own experiences relating to the importance of protective sports equipment.

Exploration (Part One):

Allow students to test materials that could be used in the outer shell of a football helmet.

Procedure:

Obtain the labeled plastic samples for testing. Set up the testing apparatus as shown. The plastic sample can be placed on top of a PVC coupling or the rim of a jar lid so that the weight can penetrate through the sample before hitting the wood. The end of the tube should be immediately above the plastic sample.

Note: the tube can be held by hand if a ring stand is unavailable. Younger students may want to hold the tube anyway – for a more secure grip.

  • Unscrew the top of the bob and attach a string so that it is centered on the bob. Lower the bob down through the tube so that it is 6 inches above the plastic sample.
  • Release the string so that the bob falls freely onto the plastic sample. Inspect the sample for cracks and breaks. Failure of a sample can be deformation that is evident on the back side of the sample, crack initiation, or complete breakage.
  • If the sample has not "failed", increase the height from which the bob is dropped by 6 inches. Keep increasing the drop test height by 6 inches each trial until the sample is broken or until you have reached a maximum of 30 inches. Record the height at which the sample breaks or the maximum height used to test it.
  • Multiply the height of the drop by the weight of the bob to obtain impact in inch-pounds.

Note: All Impact Standard testing is done in the English system in the Educational Innovations Lab Activity but this can easily be converted to metric units. The unit of measure for the impact test is the inch-pound. If a 10 pound weight is dropped an inch onto the sample, then it equals 10 in-lb.Students will be using an 8 oz plumb bob (or 0.5 lb.). The plumb bob will be dropped through a tube from increasing heights onto the plastic sample.

Assessment for Exploration (Part One):

Make sure students are following proper laboratory procedures. Monitor the groups and make sure they are recording information on their worksheets. Collect and evaluate student worksheets for completeness and accuracy.

Explanation for Exploration (Part One):

After completion of testing and recording of data, students should report their findings and determine the most suitable outer shell material for use in a particular type of helmet, of the ones tested, based on their results. There are no wronganswers here as long as students can back up their statements using evidence from their data.

Ask students to explain impact resistance and its importance in determining materials to be used in the outer shell of a helmet. Make sure they know that impact resistance describes how a material reacts to a shock or sudden stress. This test measures the brittleness of a material that has been subjected to an intense blow. The property of toughness describes the material's ability to withstand such an impact.

To relate student testing to product development in industry let students know that most product engineers do not use the results from impact tests alone to determine which material will be used in a commercial product. Decisions may also involve information gathered from tests such as stress/strain, tensile strength, ductility, or thermal sensitivity. However, this lab concentrates on the impact resistance of polymers that could be used in constructing sports equipment.

One test used in industry is the Gardner Impact Test. During this test, a weight is dropped from a specified height onto a test sample until it breaks. Although the sample may be any size, industry typically uses a 3 x 5-inch sample with a 1/16 to 1/4 inch thickness. (Since a teacher needs to use whatever materials are readily available, sizes in this lab may vary. It is suggested that samples should be as reasonably close in size as possible.)

Temperature is a major variable during testing. Most industrial tests are conducted at 20° C. These tests will be conducted at room temperature.

The discussion in this section can now lead to the importance of the foam linings placed inside of helmets. This leads you into Exploration 2.

Exploration (Part Two):

Allow students to investigate the properties of various polymer materials that could be used to create the interior cushioning and lining of the football helmet. Testing will be used to assess a material's ability to protect an object (such as a head!). Weights will be dropped on various foam materials placed over a "fragile" candy bar. Students will be able to determine which materials offer the best impact attenuation and even be able to design their own materials for testing.

Procedure:

  1. Using one type of foam material, set up the apparatus as shown below.
  1. Hold the plumb bob, narrow end pointed downward at the top of the tube. Drop the bob through the tube. Visually try to see how far the foam is compressed. Measure the indentation.
  2. Remove the foam material from the top of the candy bar. Check the bar for breakage and cracks.
  3. Repeat the drop test from the same height using the other available foam materials.

Note: The candy bars can be frozen. If so, they will show even more damage resulting from the drop. Allow students to suggest and try their own testing procedures if reasonable.

Extension (Optional):

Allow students to design their own protective packing material. Mix various combinations of ground up foam and rubber with a small amount of white glue. Two sample recipes are provided.

  1. Mix 1/4 cup foam with 1/4 cup rubber and 3 tsp of white glue. Press the mixture into two cups of a muffin tin with a spoon. Allow the mixtures to dry 48 hours before testing.
  2. Mix 3/8 cup foam with 1/8 cup rubber and 3 tsp of white glue. Press the mixture into two cups of a muffin tin with a spoon. Allow the mixtures to dry 48 hours before testing.

Students can also fill the muffin tin cups with foam sealants from spray cans such as Dow's Great Stuff™ insulating foam sealant. Great Stuff™ can also be sprayed directly onto wax paper. Repeat the drop tests using the new packing materials and compare results.

Assessment for Exploration (Part Two):

Make sure students are following proper laboratory procedures. Monitor the groups and make sure they are recording information on their worksheets. Have students report their findings. This can lead to a discussion on different types of helmets and the use of rigid foam in some and soft foam in others. Again, any student answer is acceptable as long as it can be supported by data.

Explanation for Exploration (Part Two):

Helmets work by bringing the head (and brain) to a relatively gradual stop upon impact. When an unprotected head strikes against a hard surface, inertia causes the brain to slam forward against the skull. This causes bruising and bleeding.

If you look inside most helmets you will see foam pads. The foam softens the shock by gradually crushing to absorb impact energy, thus cushioning the blow. This slows the stopping process from about 1 millisecond to 6 milliseconds, thus reducing the spike of energy to the head and brain. As the foam crushes or deforms, it converts some of the crash energy into heat.

According to the Law of Conservation of Energy, energy is not lost but converted to some other form of energy. What a helmet does during a crash is referred to as “energy management”. Some of the energy of the collision is converted to heat.

Current helmets perform energy management with some type of foam. There are two types of foam: one type is stiff and crushable, the other is rubbery or squishy. Their characteristics make it possible to design a helmet for one very hard impact, a number of hard impacts, or a very large number of softer impacts. Denser foams resist very hard impacts. Softer foams compress more easily in lesser impacts giving better protection against milder injuries. Crushable foams are ideal for helmets designed for one hard impact (like bike helmets). When the foam crushes, it does not bounce back like a spring to make the impact worse. Rubbery foams (football and skateboard helmets) provide multiple impact protection but are less protective in very hard impacts.

Elaboration:

The instructor may choose to present information on the actual plastics used in various helmet types or have students research this information on the Internet. Students might try to hypothesize why one material is favored for football helmets and others for baseball or biking helmets. Encourage students to suggest and try their own testing methods on the plastics.

Final LessonAssessment:

Have students write a short report on their findings. This report can be collected and evaluated or given orally to the class.

Sample Lesson Pictures:

Josh, my graduate fellow, is presenting the intial engagement portion of this lesson…

Josh, in the helmet, is helping students to perform the lab tests in the exploration (Part One) activity…

Students are each performing the tests in the Exploration (Part One) activity…

The students in the last block decided to perform a high impact test by putting their tubes together and testing materials again….inquiry learning usually leads to additional activities (and learning) such as this.