- 12-volt battery
- Insulated wire
- Alligator clip
- Light bulb
- Sample (steel or polymer)
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General Safety Guidelines
Answers to Post-lab Quiz
Since the physical properties of polymers are a big part of why they are useful, it is important for students to learn about those properties firsthand. Since polymers are often used to replace metals, this activity compares the physical properties of polymers with those of some common metals.
This is really five activities investigating five different physical properties. The students will be divided into five groups. Five tables will be set up, each a station for carrying out one of the activities. The five groups will rotate from station to station so that all students can perform all five activities.
This activity requires five tables because five different physical properties will be investigated. Label each table with the name of the property to be investigated there. The five physical properties are:
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1. Mass
2. Strength
3. Ductility
4. Conductivity
5. Temperature stability
Mass
At this table, provide the students with containers containing about equal volumes of steel
nuts or washers, a plastic, and a polystyrene or polyurethane foam. Students will simply
pick them up and feel the relative masses. Students should conclude that plastics and foams
are much lighter than steel.
Strength
At this table, provide pieces of steel, and a brittle plastic such as polystyrene and a
high-strength plastic such as polycarbonate. Label them polymer A and polymer B. The students
will be asked to break each piece. The students should conclude that steel is strong, while
plastics can be strong or not so strong.
Ductility
At this table, provide the students with an aluminum can or steel wire, or some other ductile
piece of metal. Also provide a piece of a soft plastic and a piece of a stiffer plastic. Label
the plastics polymer A and polymer B. The students will be asked to try to bend and reshape the
samples. They should conclude that metals are ductile, while polymers can be ductile or not
ductile.
Conductivity
At this table, provide an apparatus consisting of a 12-volt battery wired to a light bulb and a
sample of steel and one each of any two common plastics, as shown in the photographs and the
schematic below. Label the plastics polymer A and polymer B. The students will be asked to try
to complete the circuit using the steel and the plastic. The students should conclude that steel
conducts electricity while polymers generally do not.
This apparatus can be built with materials found at any electronics store. For wires it is best
to use jumper leads (insulated wires with alligator clips at each end) so you won't have to
solder any of the connections. Also, be sure to use a 12V light bulb, and that it has terminals
to which alligator clips can be attached. Such bulbs are available form Radio Shack, cat. no.
272-336.
Temperature Stability
At this table, provide the students with samples of steel, polystyrene, and polycarbonate or
nylon, a hot pot in which to boil water, and tongs. Label the polymer samples polymer A and
polymer B. Using the tongs, the students should place each sample in the boiling water for
several minutes. The steel will be unaffected, as will the polycarbonate. The polystyrene will
undergo its glass transition, and will become flexible rather than rigid. The students should
conclude that while steel is very resistant to high temperatures, polymers may or may not be
temperature resistant.
Note: Because of the risk involved with using boiling water, you
may want to carry out the hands-on work at this table yourself for the students to watch.
Relevant National Science Education Standards
Schematic for the conductivity apparatus.
Physical Science — The activity
investigates the physical properties of metals and polymers.
For more information, at other websites...
Mechanical Properties of
Polymers — learn the difference between strength and toughness, and much more, part
of The Macrogalleria from the University of Southern Mississippi.