Menu

Safety Advanced Preparation Pre-Lab Assessment Post-Lab Assessment Extra Help

Answers to Applications Assessment Rubrics Extension Relevant National Science     Education Standards

Safety

As this activity involves pulling rubber bands until they break, all students should wear eye protection at all times. When a rubber band breaks, it could snap and hit a student in the eye.

Advanced Preparation

For test samples you will need to provide the students with rubber bands, strips cut from garbage bags, and nylon fishing line. Remember, the students are carrying out what's known in the business as "destructive testing," so be sure to have enough samples for each group to carry out several tests. Cut the garbage bags into strips about 1inch by 4 inches long. Since the polyethylene chains in most garbage bags are oriented in one direction, cut test strips both vertically and horizontally to find out the direction of the orientation. Stretch the strips out, and the strip cut with the orientation will stretch much further than the strip cut perpendicular to the direction of orientation. Once you've figured out the direction of orientation, cut all strips lengthwise in that direction.

Pre-lab Assessment

The student answers will vary, but they should be specific about their planned course of action. Please see Extra Help section for a procedure. Please see the Assessment Rubrics for grading suggestions.

Post-Lab Assessment

The student table should be easy to follow and well organized. If you would like to provide a table for your students, one is provided in the Extra Help section. The report should answer all questions and be well written. Please see the Assessment Rubrics for grading suggestions.

Sample Table:

	Breaking Test			Recovery Test
material	original length of sample	length at breaking point	percent elongation	original length of sample	maximum length without permanent deformation	percent elongation
rubber band	10.0 cm	58.9 cm	589 %	9.2 cm	42.6 cm	463 %
plastic garbage bag	7.1 cm	12.1 cm	170 %	6.4 cm	6.6 cm	103 %
nylon fiber	14.2 cm	20.2 cm	142 %	17.6 cm	18.2 cm	103 %

Extra Help

The laboratory exercise is inquiry based. If you would like to provide a procedure for your students, one is given below. To view a easily printed version of this procedure, click here.

Procedure

A. Elongation at Break Test

1. Lay the yard stick across the table.br>
2. Measure the length of the rubber, plastic, and fiber samples to be tested; record them in your laboratory notebook.
   
3. Using two pair of needle-nosed pliers, grasp the sample at each end. Hold one end of the sample at "0" on the yard stick. Slowly stretch the other end of the sample as far as it will stretch, until the sample breaks. This is best done with two students, each holding the sample at one end. Note how far you had stretched the sample when it broke. Record this in your laboratory notebook.
   
4. Using the formula below, calculate percent elongation at the point of breaking. Record this information in your laboratory notebook.
   

1. Lay the yard stick across the table.
   
2. Measure the length of the rubber, plastic, and fiber samples to be tested, and record them in your laboratory notebook.
   
3. Using two pair of needle-nosed pliers, grasp the sample at each end. Hold one end of the sample at "0" on the yard stick. Slowly stretch the other end of the sample in small increments. After each increment, release the sample to see if it will return to its original length. This is best done with two students, each holding the sample at one end. Note the longest distance you can stretch the sample without having the sample stretch permanently. Record this in your laboratory notebook.
   
4. Using the formula below, calculate percent reversible elongation. Record this information in your laboratory notebook.
   

Answers to Applications

1. A cowpoke who needs rope for rounding up cattle
   fiber
   examples: polypropylene, nylon, poly(ethylene terephthalate)

2. A carpenter who wants to build a house with shatterproof windows
   plastic
   examples: polycarbonate, poly(methylmethacrylate)

3. A bungee jumper who needs a new bungee cord
   rubber
   examples: polybutadiene, polyisoprene, polyisobutylene, polychloroprene, silicones

4. A knitter who needs yarn for making socks
   fiber
   example: polyacrylonitrile

5. A guitar player who needs new strings
   fiber
   examples: nylon, polypropylene, poly(ethylene terephthalate)

6. A veterinarian who needs surgical gloves
   rubber
   examples: polybutadiene, polyisoprene, polyisobutylene, polychloroprene, silicones

7. A. easy to stretch, hard to permanently deform
   B. easy to stretch, easy to permanently deform
   C. hard to stretch, hard to permanently deform

Assessment Rubrics

Pre-lab

Points	5	4	3	2	1	0
Procedure	Plan includes a step-by-step procedure that is easy to follow.	Plan includes a procedure with most steps.	Plan includes a procedure with some steps.	Plan includes a procedure with few steps.	Plan includes an overview of the procedure.	Plan does not include a procedure.
Criteria	Plan includes clearly stated criteria for testing and type of data.	Plan includes criteria and data, but not clearly stated or not well outlined.	Plan includes criteria and some data to be collected.	Plan includes some criteria and some data to be collected.	Plan mentions some data that should be collected.	Plan does not mention criteria or type of data.

Post-Lab

Points	5	4	3	2	1	0
Table	Table is easy to read, well organized, and contains all data.	Table is easy to read and contains all data, but is not well organized.	Table is easy to read and contains most data.	Table contains some data, but is easy to read.	Table is incomplete and hard to read.	Does not have a table.
Report	Report addresses and answers all questions completely, thoroughly, and clearly.	Report addresses and answers all questions completely.	Report addresses and answers most questions completely.	Report addresses and answers most questions.	Report addresses and answers some questions.	Report does not address or answer questions.
Conclusions	Makes reasonable conclusions that are well explained.	Makes reasonable conclusions that are somewhat explained.	Makes reasonable conclusions that are not explained.	Makes some conclusions but offers no explanation.	Makes some conclusions but some are not reasonable and are without explanation.	Does not make any conclusions.
Grammar, etc.	The student has no grammatical errors or misspelled words in the report.	The student has few grammatical errors or misspelled words in the report.	The student has some grammatical errors and misspelled words in the report.	The student has several grammatical errors and misspelled words in the report.	The student has many grammatical errors and many misspelled words in the report.	The student has many errors making it difficult to understand the content of the answers.

Extension

For a more in-depth look at the differing properties of rubber, plastics, and fibers, have the students measure not only the distances that they can stretch their samples without deforming or breaking them, but also the force (and by calculation, energy) involved with breaking or deforming. This can be done using an apparatus like the one described in the activity How Strong? Read the "Extension" section of that activity for an explanation of the physics involved.

Relevant National Science Education Standards

Unifying Concepts and Processes — The experiment is centered around measurement of tensile deformation.

Science as Inquiry — The activity is inquiry based.

Physical Science — The activity compares the relative physical properties of rubber, plastics, and fibers.

Science and Technology — The activity shows how engineers must choose materials for practical applications based on diverse physical properties. The activity provides an opportunity to stress that polymer scientists seek to create materials with specific desired properties by deliberately manipulating molecular structure and, in the case of composite materials, other parameters.

History and Nature of Science — The students should understand the nature of the knowledge they gain in this experiment as being scientific in that it arises solely from their observations.