retracting cat’s claw

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Cat claw mechanism

structure and function of cat claw

There are many examples of engineering in nature. A cat’s retractable claws make use of a lever. When not needed for hunting or self-defense, climbing, kneading, or for extra traction on soft surfaces, the cat retracts its claws.

Sharp and ready to use

It is hard to improve on nature, but there is much to learn from understanding how these mechanism work. Think about the cat’s paw as a design challenge. Each question corresponds to a step in the Engineering Design Process. A cat needs to use its sharp claws for some activities, without wearing them down when not in use. This retractable claw arrangement meets the needs.

Cat’s claws are held in place by ligaments, but are able to be rotated outward through the use of specific muscles and tendons. The cat’s claws stay tucked in the fur and skin between its toe pads when not needed.

  • Ask (What? Ask questions, understand the need, identify the problem, define)
    Cats extend their claws for hunting or self-defense, climbing, kneading, or for extra traction on soft surfaces. The claws stay sharp because they are not worn down when they are just walking normally. By retracting them when not needed, it reduces their exposure and wear. By waiting to extend its claws until they are needed, the cat prevents excessive noise from the claws contacting a hard surface.
    Q: How can a cat keep its claws sharp? How can a cat move silently?
  • Imagine (So what? Imagine, brainstorm, explore, discover)
    The curve of the claw is important. As the cat grows and uses its claws, they will grow too. Imagine the claw wasn’t curved. Examine the design of the claw and define traits that work together to make the claw function efficiently.
    Q: Would the rotating extension be as effective if they were straight? Would the claw then need a larger range of motion to get out of the way when not in use?
  • Plan (Now what? Plan, design)
    The claws need to be able to move out far enough to contact surfaces and hold tightly. The cat may need to extend the claws in only one foot.Analyzing a pre-existing design and improving upon it after seeing how it performs is a big part of engineering.
    Q: Can you improve on the design of the claw? Can you spot anything that would make the claw work better?
  • Create (Do it. Create, try it out)
    Cat’s claws are held in place by ligaments, but are able to be rotated outward through the use of specific muscles and tendons. The claw material stays sharp. It can be sharped as it wears down and grows.
    Q: To build a working prototype, what materials must be provided?
  • Improve (If this then what? Improve, make it better)
    Can you improve on the design of the claw? Can you spot anything that would make the claw work better? Analyzing a pre-existing design and improving upon it after seeing how it performs is a big part of engineering. There are many new man-made materials that have the same properties as cat’s claws.
    Q: What materials or tools do you need to improve your prototype? How could you make your prototype function better than a real cat’s claw?

Engineering vocabulary, concepts

  • lever, pulley

Show and Tell
Now it is your turn. Here are some challenges for you to work on…

  • find some illustrations of cat paw bones and tendons
  • recreate the claw retraction action with Connects or LEGO xx
  • using CAD or drawing software to make your own model of the claw retraction mechanism
  • learn about man-made materials that are strong and light like cat’s claws
  • build a working prototype out of the materials provided
  • What materials or tools do you need to improve your prototype? How could you make your prototype function better than a real cat’s claw?

Learn more…

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