Students will learn about different materials that bikes are made out of. Students will learn about different factors, material strength, flexibility, cost, weight etc. that affect an engineers decision when choosing a material to use in constructing a prototype/real thing.
To apply this information, students will test and rate the strength of different types of materials. They will record the strengths on a chart and compare the different materials. Students will discuss the factors that affect an engineer’s choice of materials.
- To explore the factors that affect material choices for a design.
- To compare strengths and weaknesses of different materials.
- Print out enough worksheets for the class (either one per group or per student)
- Optional: Set up large version of real bike materials sheet.pdf or make copies for each group to look at.
- Arrange students into groups.
- Distribute materials and worksheets.
Engineers need to keep a lot of things in mind when choosing what material they will use in their designs.
A bike will have two types of loads. The Static Load – the bike frame must support itself – and the Dynamic Load – the bike frame must support changing forces of a cyclist’s weight, forces of pedaling and breaking, road’s surface (bumps, holes)
Friction – or the resistance of the road’s surface. This factor affects the engineers decision on what a tire should be made out of and how it should be designed. Road bikes want to reduce friction for faster movement v. mountain bikes, which want wide tires for increase friction to reduce falls.
Materials that engineers choose for their designs must withstand all of these forces. There are three categories of material properities that enable bikes to function to suit different purposes
Physical: Density, color, electrical conductivity
Chemical: Reactivity, rust resistance, solubility, reaction to heat.
Elasticity: When a material can be bent and come back to its original shape.
Yield Strength: The point at which a material is bent and it keeps the new shape.
Ultimate Strength: The point at which a material is bent and it breaks.
Explain the concepts mentioned in the Teacher Background section. Tell students about the things that engineers must keep in mind when choosing a material.
Go over Static and Dynamic Loads, and discuss the differences.
Go over friction on tires – when you might want more friction (mountain bikes) and when you might not (racing road bikes).
Talk about physical, mechanical and chemical properties (e.g., physical – weight of the bike for easy of carrying; mechanical – the amount of weight the bike must hold without breaking; chemical – rust resistance for a long-lasting frame).
Talk about elasticity, yield strength, and ultimate strength and how these strengths are different and necessary (e.g., a bike frame should have a high ultimate strength but should not be easily bent, even if it does return to it’s original shape).
Discuss why engineers choose certain materias and why they avoid others. Remind students that there are reasons other then strength. Talk about costs, looks, availability, appearance, durability, aerodynamics etc.
As a class, go over the attached chart labeled “Real bike materials sheet”.
Evaluate the differences between steel, aluminum, carbon and titanium.
What are the pros and cons of each material?
Ask students what material they would choose to build themselves a bike.
Distribute materals to the class and give instructions on the activity.
Tell them that they are researching the pros and cons of five different materials.
Pass out the ‘Activity Worksheet’ and materials to be tested. Explain the test categories.
Looks – rate from 1 – 10 the way this material would look on a bike frame.
Weight – rate from 1 – 10 how heavy the material is.
Cost – Rate from 1 – 10 the cost of the material (help students who do not know relative pricings).
Elasticity – rate from 1 – 10 how much the material returns to its original shape when bent.
Yield Strength – rate from 1 – 10 how easy is it to bend the material out of shape.
Ultimate strength – rate 1 -10 how easy it is to break the material.
Have students fill out the chart for the five materials.
When the student have finished testing, have them return to their seats to discuss the activity. Ask:
Which was the best material?
Were any of the materials strong in all of the categories?
What are the trade-offs to using one material over other materials?
Which materials were the strongest (high yield strength and ultimate strength)?
If you had to build a bike out of these materials what material would you choose?
What are other factors we could have considered?
Extensions or Modifications:
- Give students limitation, such as cost or weight, and have them choose the best material.
- Talk about what material would be best for a different item (cars, computers, kitchen appliances, etc.).
- Add different material to the list to test.