Contextualization

Elastic force is a type of restoring force that appears when an object is deformed by an external force and seeks to return to its original shape as soon as this external force is removed. If you have ever stretched a spring or a rubber band, loaded a bow or a crossbow, or even squeezed a rubber ball, then you have experienced elastic force.

According to Hooke's Law, in many materials, the length of deformation is directly proportional to the applied force. That is, the more the spring, the rubber band, or any elastic body is stretched or compressed, the greater the elastic force exerted by it. The work done by the elastic force is the energy stored in the body being deformed. This energy is called elastic potential energy.

Elastic force is a vital part of many natural and artificial systems and phenomena: it is responsible for maintaining the shape of living cells, it is the force that allows bungee jumpers to return safely, and it is the force that makes spring-driven clocks work. In this project, we will delve deeper into the nature of the work of elastic force and better understand the role it plays in our world.

Elastic force has a wide range of applications, from the molecular structure of materials to the engineering and design of machines and buildings. In the field of medicine, for example, the elastic force of arteries and veins helps maintain blood pressure and blood flow. In civil engineering, elastic force is crucial in designing structures that can withstand wind and seismic forces. In short, a solid understanding of the work of elastic force is essential for a wide variety of disciplines.

To explore this concept in greater depth, we suggest the following resources:

• Elastic Force Work - Mundo Educação
• Elastic Force and Hooke's Law - Brasil Escola
• Elastic Force and Materials - Só Física

Practical Activity

Title: Designing and Testing Catapults: An Exploration of Elastic Force

Project Objective

This project aims to offer students a practical experience of how the work of elastic force plays a crucial role in the operation of catapults, an invention that dates back to antiquity and uses the potential energy stored in an elastic source to launch projectiles over long distances. In addition, students will be challenged to conceive, build, and test their own catapult models, providing them with the opportunity to apply many of the concepts learned in the classroom and to see firsthand how theory translates into practice.

Detailed Project Description

The construction of the catapult model will be divided into several stages: conception, design, construction, testing, and optimization. Students will have to cooperate and collaborate throughout the project, applying their problem-solving, communication, and time management skills.

The project will address various topics, including Hooke's Law, elastic force, the work of elastic force, elastic potential energy, and the physics of projectile motion. In addition, the project will have an important interdisciplinary component, as it will involve concepts of geometry, technical drawing, materials engineering, history, and even writing and research.

Required Materials

• Wooden sticks
• Rubber bands
• Glue
• Mini marshmallows or small paper balls
• Ruler
• Projector (for technical drawing)
• Graph paper
• Pencils and pens
• Computers with Internet access for research and writing

Detailed Step-by-Step for Activity Execution

1. Research and Catapult Design: Each group should research different catapult designs, learn about their history, and the functioning of the principle of launching projectiles using elastic force. Each group will then design their catapult, presenting it in a detailed technical drawing, using concepts of geometry and measurements.

2. Catapult Construction: Using the provided materials and following the design they conceived, students will build their catapult model.

3. Catapult Testing: Each group will test their catapult, recording the results in terms of distance, accuracy, and consistency for different applied forces (e.g., different degrees of stretching of the rubber bands).

4. Catapult Optimization: Based on the test results, each group may make changes and improvements to their catapult design and construction before conducting a second cycle of tests.

5. Project Report: After completing the practical part of the project, each group should work together to write a detailed project report. The report should include: an introduction contextualizing the theme and the project; the development detailing the theory of elastic force, the design and construction of the catapult, and the methodology and results of the tests; a set of conclusions drawn from the project; and a list of references of all materials consulted.

Project Deliverables

Each group must produce the following deliverables:

• Technical drawings of the designed catapult.
• The physical model of the catapult.
• Project report, which should include:
  • Introduction: Contextualizing the theme and the project objective.
  • Development: Detailing the theory of elastic force, the design and construction of the catapult, as well as the methodology and results of the tests.
  • Conclusions: Explicitly stating the learnings obtained, the conclusions drawn about the project, and how they relate to the theory of elastic force studied in the classroom.
  • Bibliography: Indicating all sources consulted during the project.

When writing the report, students should ensure they are communicating clearly and effectively, graphically representing test results when appropriate and explaining how they validate or challenge the theory studied. The report should be written in clear and precise language, with an emphasis on coherence and the correct use of physical concepts.