A cardboard claw grabber is a fun school project that lets you pick up small objects without touching them directly. It can be made from simple materials like cardboard, brads, string, tape, and rubber bands. The project matters because it turns a craft activity into a working model of a real machine.
Students can see how force, motion, and design choices affect how well the claw works.
Key Facts
- A lever turns around a fixed point called a fulcrum.
- Mechanical advantage = output force / input force.
- Longer handles can make a claw easier to squeeze because they increase torque.
- Torque = force x lever arm distance.
- A linkage connects moving parts so one part can control another part.
- Rubber bands can store elastic potential energy and help the claw open again.
Vocabulary
- Lever
- A lever is a stiff bar that pivots around a point to move or lift something.
- Fulcrum
- A fulcrum is the pivot point where a lever turns.
- Linkage
- A linkage is a set of connected parts that transfer motion from one place to another.
- Torque
- Torque is a twisting effect made by a force acting at a distance from a pivot.
- Prototype
- A prototype is an early test version of a design that helps you find and fix problems.
Common Mistakes to Avoid
- Making the cardboard jaws too thin, which is wrong because weak jaws bend instead of gripping the object.
- Placing the pivot holes unevenly, which is wrong because the two jaws will not line up or close smoothly.
- Pulling the string straight without guiding it, which is wrong because the force may not move the linkage in the direction needed to close the claw.
- Using too much tape on the moving joints, which is wrong because the joints need to rotate freely for the claw to work.
Practice Questions
- 1 A claw handle is 12 cm from the pivot, and a student squeezes with 5 N of force. What torque does the student apply?
- 2 A cardboard jaw has a mechanical advantage of 2. If the input force is 4 N, what output force can the jaw apply?
- 3 If your claw closes well but will not open again, which part of the design should you adjust first, and why?