Author: Jake Saylor
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC-1161732.
Students explore how spiders create their webs and the properties of the webs to catch food. This includes exploring the viscosity and velocity of the solution to see how they impact the drop size of the "glue" on the silk.
What should students know as a result of this lesson?
What should the students be able to do as a result of this lesson?
Castor oil, olive oil, tomato juice, milk, corn syrup, nylon string, ruler. Nylon string can be purchased at a craft store or music store as guitar string.
Instructor Setup: You will need to cut 5 pieces of nylon string for each lab group. The string length should be about 15 inches for each piece. The students should have access to rulers at their lab station. Place an appropriate amount of solution in a plastic container for the students to run their strings through. Depending on the class size you may want to do 2 solution containers for each one and split the class up. An alternative method would be to have the students use beakers for the solution at their individual lab stations.
In Figure 2 on the worksheet compare the two pictures and notice how the size of the doplet is different as well as the wavelength of the drops. What variables might impact the size of the drop on the string? Guide students toward viscosity and velocity: How does type of material (viscosity) affect droplet size and wavelength of drops? How does the speed of the string through the solution affect the droplet size?
Students will perform a lab changing the viscosity of fluid as well as the velocity to determine how the drop size changes. Pass out the worksheet for the lab that details the procedure for the students. Observe the students following the procedure.
Students will answer analysis questions regarding the lab they completed discussing things such as viscosity and wavelength. The wavelength is the distance from one point to the next similar point. Viscosity is the resistance for a fluid to flow. Also, students will answer application questions involving how spiders would spin their webs to create certain sized drops of glue. The higher viscosity and faster velocities means larger bead size.
Advanced classes may complete Mathematical Models of "beads-on-a–string" to do some calculations involving the drop size.
Spiders have used webs as a method to catch food for thousands of years. Spiders spin webs using silk as a means to trap their prey so that they do not have to move around and chase their prey. The spiders use different glands to produce different kinds of silk. How do the flies and insects stick to the webs? The main way the prey is stuck to the silk is through tiny drops of glue that are produced and placed on the silk fibers as pictured below. This is referred to as beads-on-a-string and consist of adhesive polymeric glycoproteins. Why do the beads form at specific ordered locations throughout the entire strand? Imagine when the water is turned off at a faucet, instead of a steady stream of water coming out, the water forms drops. This is the main principle behind Raleigh instability, that is, that liquids because of their surface tension tend to minimize their surface area. This means the liquids will naturally tend to form drops when the wavelength reaches a certain maximum. This forms the specific pattern you see pictured in Figure 1 of the worksheet The wavelength is the distance from one point to the next similar point. For example, in Figure 1 of the worksheet, the wavelength could be measured starting with the far left side of the bead on the left and go to the left most side of the bead in the center.
What factors may influence the size of the drops? One of the main factors is the viscosity of the glue that the spiders use. Viscosity is the resistance of a fluid to flow. The higher the viscosity of a fluid the harder it is for the material to flow. For example, water would have a low viscosity because it is easier to move than honey which would have a high viscosity.
Common Core Standards:
Students should be familiar with basic lab safety rules. Wash hands after dipping strings through solutions or if available wear gloves. Wear safety goggles to prevent solutions from entering eyes.
Through the production of spider webs. This research is currently being used in adhesives such as glues and tapes.
Lab data collection, analysis and application questions.
Grouping Suggestions: Depending on the class size you may want to do 2 solution containers for each solution and split the class up so that one half of the room uses one set of solutions. An alternative method would be to have the students use beakers for the solution at their individual lab stations. Students should be in groups of 2 or 3.
Pacing/Suggested Time: A 45 min. period should be allowed to complete the lab and questions. I would suggest doing the introduction and background information the day before.