Friction

Kathleen Cummings Dominguez    Sabin Magnet
                               2216 W. Hirsch
                               Chicago, IL 60622
                               312 534-4491

Objectives: 

    Students will demonstrate a greater understanding of "friction" by 
cooperatively experiencing and describing a range of phenomena involving 
friction.  Students will understand the term "static friction" and the ratio
of friction and weight as it relates to moving an object at rest. 

Materials needed:

For each student: wooden sticks, (i.e, popsicle, candied apple and chop sticks)
                  one empty thread spool 
                  metal, plastic, cork and rubber washers
                  rubberbands, assorted sizes
For each group: set of slotted weights
                miniature parachutist
                small pan (plastic, from microwave dinners) with a hole for 
                     tying the string
                blocks 
                spring scale              
For teacher's demonstrations:
     Two identical, cylindrical, glass bottles (with tops), filled with various 
          quantities of water 
     One wooden slope, at least as wide as the bottles, with sandpaper glued to 
          the reverse side* and two 2" X 4" X 8" blocks 
     The teacher wears a pair of jeans with worn knees and a shirt or sweater 
          with worn elbows 
     Various surfaces for lunar vehicle runway: smooth, *sandpaper, large frozen 
          tray of ice, carpeting, etc. 
     One "slimey" ball 
     One crystal wine glass half full of water 
     Detergent for washing hands and vinegar 
     One spool of thin string 
     One pre-made "air car" made from a thread spool, cardboard square and a 
          balloon  
     Balloons
     Foam rubber mats of different textures, 24" X 24"
     Column of coins
     Sound tubes

Strategy:

1.  Teacher throws a "slimey" ball on the chalkboard and asks students how the 
ball moves.  She rubs an edge of a wine glass to get the glass to sing.  She 
asks the class how it happens.  If they don't know, they are told friction did 
it.  Students are asked to rub their hands, then really hard, and tell what 
happens.  The teacher rotates the sound tubes so the students can hear and asks 
the class what makes the sound. 

2.  Teacher asks students, grouped into cooperative teams, to list examples of 
friction and then to write a good definition.  Answers are written on the board.
Class synthesizes answers into one good definition.  Students are led to 
understand that friction can be associated with solids, liquids and gasses and 
that there are subtle examples as well as flagrant examples.  Teacher asks 
individual students to move a column of coins with one finger on the top of the 
column.  (Teacher demonstrates how to do it: by pressing hard on the top coin on 
the edge closest to her). 

3.  Students are shown how to make a "lunar vehicle" with the thread spool, 
various rubberbands, washers and sticks.  Students are to predict and/or test-
out the best type of components to use which will most effectively use friction 
to make the vehicle run.  Students test their lunar vehicle on various surfaces, 
i.e., wood, sandpaper, rug, ice and table top.  Each group selects its best 
lunar vehicle to compete with other teams in a race on the indoor/outdoor 
carpeting. 

4.  Teacher asks groups to predict what will happen with the two bottles which 
she is about to let roll down an incline.  Students will understand that water 
creates friction on the glass and slows down and stops that bottle's movement 
sooner than the empty bottle stops. 

5.  Teacher asks teams to predict what will happen to the contraption called an 
"Air Car" when she lets it go.  Students will learn that air can reduce friction 
and overcome gravity. 

6.  Each group is given a little parachutist, asked to throw him/her into the 
air, observe and write an explanation as it relates to friction.  Each group 
reads their answer to the class.  Students will learn how air can be used to 
oppose the force of gravity. 

7.  Groups experiment with various weights and friction using the pan, string, 
weights, spring scales and various surface textures.  The groups are asked to 
collect data as weight is added to the pan.  Students will understand the ratio 
between weight and the force required to move the weight to overcome static 
friction, i.e., to move a mass from rest. 
          Coefficient of Friction: mu = FFR/N