Subject: Gears

Overview:Biking is fun for all ages, but can be tough unless you’re in the right gear. A bike’s gear system is designed to make pedaling more efficient on different terrains. The gear ratio measures how many times the back wheel turns for each rotation of the pedals.

Objective: SWBAT understand the gear settings on a bicycle, investigate gear ratios, develop understanding of general bicycle maintenance and safety through hands on activities and experiments.

NSTA National Science Education Standards

1.2 ( Grades: K-12 ): The goal of this standard is to think and analyze in terms of systems. Thinking and analyzing in terms of systems will help students keep track of mass, energy, objects, organisms, and events referred to in the other content standards. The idea of simple systems encompasses subsystems as well as identifying the structure and function of systems, feedback and equilibrium, and the distinction between open and closed systems.

E.1.1.a ( Grades: 5-8 ): Students should develop their abilities by identifying a specified need, considering its various aspects, and talking to different potential users or beneficiaries. They should appreciate that for some needs, the cultural backgrounds and beliefs of different groups can affect the criteria for a suitable product.

E.1.4.a ( Grades: 5-8 ): Students should use criteria relevant to the original purpose or need, consider a variety of factors that might affect acceptability and suitability for intended users or beneficiaries, and develop measures of quality with respect to such criteria and factors; they should also suggest improvements and, for their own products, try proposed modifications.

E.1.5.a ( Grades: 5-8 ): Students should review and describe any completed piece of work and identify the stages of problem identification, solution design, implementation, and evaluation.

E.2.4 ( Grades: 5-8 ): Perfectly designed solutions do not exist. All technological solutions have trade-offs, such as safety, cost, efficiency, and appearance. Engineers often build in back-up systems to provide safety. Risk is part of living in a highly technological world. Reducing risk often results in new technology.

E.2.5 ( Grades: 5-8 ): Technological designs have constraints. Some constraints are unavoidable, for example, properties of materials, or effects of weather and friction; other constraints limit choices in the design, for example, environmental protection, human safety, and aesthetics.

Benchmarks for Science Literacy

11A/M3 ( Grades: 6-8 ): Any system is usually connected to other systems, both internally and externally. Thus a system may be thought of as containing subsystems and as being a sub-system of a larger system.

12B/E1 ( Grades: 3-5 ): Make calculations when necessary to solve real-world problems and decide whether to make the calculation mentally, on paper, or with the help of a calculator or computer.

1C/M8 ( Grades: 6-8 ): Scientists' personal interests and viewpoints can influence the questions they investigate.

3A/M3 ( Grades: 6-8 ): Engineers, architects, and others who engage in design and technology use scientific knowledge to solve practical problems. They also usually have to take human values and limitations into account.

3B/E1 ( Grades: 3-5 ): There is no perfect design. Designs that are best in one respect (safety or ease of use, for example) may be inferior in other ways (cost or appearance). Usually some features must be sacrificed to get others.

3B/E2 ( Grades: 3-5 ): Even a good design may fail. Sometimes steps can be taken ahead of time to reduce the likelihood of failure, but it cannot be entirely eliminated.

3B/E3 ( Grades: 3-5 ): The solution to one problem may create other problems.

3B/M1 ( Grades: 6-8 ): Design usually requires taking into account not only physical and biological constraints, but also economic, political, social, ethical, and aesthetic ones.

3B/M2a ( Grades: 6-8 ): All technologies have effects other than those intended by the design, some of which may have been predictable and some not.

3B/M4a ( Grades: 6-8 ): Systems fail because they have faulty or poorly matched parts, are used in ways that exceed what was intended by the design, or were poorly designed to begin with.

3B/M4b ( Grades: 6-8 ): The most common ways to prevent failure are pretesting of parts and procedures, overdesign, and redundancy.

3C/E4 ( Grades: 3-5 ): Factors such as cost, safety, appearance, environmental impact, and what will happen if the solution fails must be considered in technological design.

3C/M2 ( Grades: 6-8 ): Technology cannot always provide successful solutions to problems or fulfill all human needs.

3C/M8 ( Grades: 6-8 ): Scientific laws, engineering principles, properties of materials, and construction techniques must be taken into account in designing engineering solutions to problems.

7E/E7 ( Grades: 3-5 ): In some groups, decisions are made by and disputes settled by recognized authorities such as parents, teachers, bosses, or elected officials.

Notes:

●If there is only one bike for the whole group, first calculate the gear ratio as a large group. Then have small groups make plans for the bike course and present them. Select two or three and discuss results.

●If there are children that cannot ride a bike, have them be recorders.

●Have bike course already mapped out before lesson

Materials:

●Bicycle with gears that can be changed

●Helmet

●Markers

●Pencils and Paper

●tape measure

●stopwatch

●chalk

●optional: calculator

Instruction:

1.Introduce bikes and gears. DIvide students into small groups and have them discuss how bikes work. (3minutes)

2. 2.Watch video clip at http://scigirlsconnect.org/page/pedal-power-video
   

3.Ask each group to brainstorm ways to go faster on a bike (pedal quickly, change gears, bike design). Then ask students to determine which gears will help them complete a set course in the shortest amount of time.

4.Assign groups Bikes and assist them in turning the bike upside down on the floor. (Make sure they are stable!) Have students count number of teeth on the gears in the front (nearest the pedals) and then in the back. Then have them calculate the possible gear ratio and order them from highest to lowest. (SEE EXAMPLE TABLE)

         gear ratio =   number of teeth on front gear

                                 number of teeth on back gear

      5. Set bikes to lowest gear (smallest gear in the front, largest gear in the back. Make a            

mark on the tire using the chalk and place chalk line in the 12 o’clock position.

      6. Slowly start to push the pedal forward while making sure to keep close count of how many revolutions the tire makes in one rotation of the pedal. Record your findings and compare to the original gear ratio calculation.

      7. Repeat step 6 for the highest gear (largest gear in front and smallest in back). What is the relationship between gear ratio and tire revolutions? How do tire revolutions relate to speed? Would you want to be in a high or low gear when you go up a hill? Down a hill? Why?

   8. Show students the test course. Give groups 10min to decide the gears to test and who will be their rider. Encourage them to think about which gears will work best on the various landscapes (low for uphill, high for downhill, middle to high for flat stretches). Then, have groups take turns riding and recording their completion times. Each student’s experience will be different so they should each ride the course a few times.

9. Have student’s record all their findings and organize them based on their completion times and gear ratios. Are gears the only factors in speed?

Reference:

http://www.pbslearningmedia.org/collection/scigirls/?topic_id=797