CONTEXT:

Many of our physical activities involve outside forces.  While some may be desirable, others can cause problems in the operation and efficiency of the equipment we use.  Efficiency is how well or effectively a piece of equipment or machinery operates, given the amount of energy that it uses.  Engineers attempt to design machines that produce the greatest amount of work with the least effort or expense.  However, external forces such as friction and drag must be overcome to produce an effective and economical design.

Different materials produce varying amounts of friction when they are placed together or move against each other.  Shape, texture and mass can each cause friction to increase or decrease.  What you learn from conducting a friction test will help dictate the way in which you design and build a machine.

By testing and comparing how materials move against each other, you can determine how to minimize or maximize frictional forces.  The knowledge you gain about friction will help you to control friction and optimize the results of your design.

CHALLENGE:

EXPLORATORY
Test several materials against selected surfaces to determine the friction generated when one material moves against another.  Create an accurate way to measure and graph the results. 

INTERMEDIATE
Design and build a machine that uses friction to help it climb upwards. The object is to maximize friction.  For example, you might study an historic toy that operates using two opposing strings that are alternately pulled to allow a clown to 'climb' the rope.  You might analyze how the toy works to determine if the slippage of moving parts has been reduced, thus improving its efficiency, or if it could be improved.  You might consider how to reduce the slipping of moving parts, such as the use of wheels or pulleys.
 
ADVANCED
Design a lightweight device that will roll, not slide, down a ramp taking the longest time possible. 

MATERIALS:

EXPLORATORY

• Sandpaper
• Strip of carpet
• Strip of rubber
• Block of wood
• Fishing line
• Pulley

INTERMEDIATE

• Cardboard
• Glue
• Plastic straws
• String or yarn
• Tape

ADVANCED

• Wood
• Paper
• Cardboard
• Rubber bands
• Glue
• String
• Tape
• Yardstick

CRITERIA:

Your success on this Challenge will be based on your completion of the activities below. Three general criteria for your performance will be: your participation in the activity; the accuracy of your measurement and model construction; and the performance of your design.  Your teacher will help you understand how your performance will be graded.

EXPLORATORY

• Gather the materials to be tested on the Test Board
• Brainstorm ideas for creative ways to accurately measure and chart results
• Draw several sketches of your test set-up; choose best design to use for presentation
• Conduct experiment
• Present your project

INTERMEDIATE

• Research historic toys that use friction to operate
• Brainstorm ideas for a machine that uses friction that will allow a device to "climb" a rope
• Gather materials
• Draw several sketches of your design; choose best design to construct
• Construct design using only the materials provided
• Test and record measurements
• Present your project

ADVANCED

• Research materials for friction qualities or conduct one or more exploratory experiments
• Brainstorm ideas for your device
• Gather materials, use only those provided
• Review the following specifications
  1. Mass of device must not exceed 200 grams
  2. Device must be able to fit into a 30 cm x 30 cm x 30 cm cube (at any time in the activity)
  3. Entire device must roll, not slide, down the ramp.
  4. Each part of the device must have the same motion. (NOTE: Devices like a "car" that have wheels that roll but a body that does not roll will be disqualified.)
  5. Wet glue or the sticky side of tape may not contact the ramp.
• Draw several sketches of you test set-up; choose best design to use for presentation
• Construct your device
• Test and present your project