Lesson Plan | Traditional Methodology | Work: Resultant Force

Objectives

Duration: 10 - 15 minutes

The purpose of this stage is to provide a clear and detailed overview of the learning objectives of the lesson. By defining the main objectives, the teacher guides students on what is expected of them to learn and understand by the end of the lesson, ensuring that everyone is aligned and focused on the same goal.

Main Objectives

1. Explain the concept of net force and how to find it in different situations.

2. Demonstrate the calculation of work done by a net force using the formula W = F * d * cos(θ).

Introduction

Duration: 10 - 15 minutes

The purpose of this stage is to capture the students' attention and provide a clear and relevant starting point for the study of net force and work. By presenting initial context and curiosities, the teacher seeks to connect the lesson topic with students' everyday experiences, making the content more accessible and interesting.

Context

To start the lesson on net force and work, begin by contextualizing the importance of studying forces in physics. Explain that forces are responsible for all movements and changes in movement that we observe in our daily lives. Provide practical examples such as the movement of a car accelerating, the fall of an apple from a tree, or the push we give to a chair to move it. Detail that understanding forces allows us to predict and control a wide range of natural and technological phenomena.

Curiosities

Did you know that net force is a crucial concept used in engineering to ensure the safety of constructions? For example, engineers need to calculate the net force acting on bridges and buildings to ensure that they can withstand heavy loads and resist natural disasters such as earthquakes and strong winds.

Development

Duration: 50 - 60 minutes

The purpose of this stage is to deepen students' understanding of the concepts of net force and work. By addressing specific topics with detailed examples and solving practical problems, the teacher ensures that students can apply theory to real situations, consolidating their learning in a practical and effective way.

Covered Topics

1. Definition of Net Force: Explain that net force is the vector sum of all the forces acting on an object. Highlight that it determines the acceleration of the object according to Newton's second law (F = ma). 2. Method to Find Net Force: Describe step by step how to find net force in different situations. Include examples of forces in the same direction, forces in opposite directions, and forces in perpendicular directions, using vector addition. 3. Work Done by a Force: Introduce the definition of work in physics, explaining that it is the product of force and the distance traveled by the object and the cosine of the angle between the force and the direction of motion (W = F * d * cos(θ)). 4. Practical Examples of Work Calculation: Present detailed examples of how to calculate the work done by a net force in different scenarios. Include solved problems that directly apply the work formula. 5. Importance of Angle in Work Calculation: Explain how the angle between the applied force and the direction of motion affects the calculation of work. Show examples of forces applied at different angles (0°, 90°, 180°) and how this influences the value of work.

Classroom Questions

1. A 5 kg block is pulled by a force of 10 N along a flat surface for a distance of 4 m. The force is applied at an angle of 30° with the horizontal. Calculate the net force and the work done. 2. A box is pushed with a force of 15 N up an inclined ramp at 45° for a distance of 3 m. Find the net force and the work done. 3. An object is pulled by two forces: 8 N to the north and 6 N to the east. Calculate the net force and determine the work done if the object moves 5 m in the direction of the net force.

Questions Discussion

Duration: 20 - 25 minutes

The purpose of this stage is to ensure that students fully understand the discussed concepts and apply them correctly. By reviewing the solved questions and engaging students with reflective questions, the teacher promotes a collaborative learning environment and reinforces the acquired knowledge.

Discussion

•  Question 1: A 5 kg block is pulled by a force of 10 N along a flat surface for a distance of 4 m. The force is applied at an angle of 30° with the horizontal. Calculate the net force and the work done.

Explanation: First, identify that on the horizontal plane, the net force is the applied force itself, as there are no other horizontal forces. The net force is 10 N. To calculate the work, use the formula W = F * d * cos(θ). Then, W = 10 N * 4 m * cos(30°) = 10 * 4 * (√3/2) = 20√3 J.

•  Question 2: A box is pushed with a force of 15 N up an inclined ramp at 45° for a distance of 3 m. Find the net force and the work done.

Explanation: On the ramp, the net force is the component of the force parallel to the ramp. The net force is F * cos(45°) = 15 N * (√2/2) = 15 * 0.707 = 10.605 N. The work done is W = F * d * cos(θ), where θ is the angle between the force and the direction of movement. As the force is in the same direction as the incline, W = 15 N * 3 m * cos(0°) = 15 * 3 * 1 = 45 J.

•  Question 3: An object is pulled by two forces: 8 N to the north and 6 N to the east. Calculate the net force and determine the work done if the object moves 5 m in the direction of the net force.

Explanation: Use vector addition to find the net force: √(8² + 6²) = √(64 + 36) = √100 = 10 N. The work done is W = F * d * cos(θ). As the movement is in the direction of the net force, θ = 0° and cos(0°) = 1. Therefore, W = 10 N * 5 m * 1 = 50 J.

Student Engagement

1. 樂 Question 1: How does the direction of the applied force influence the calculation of work done? 2. 樂 Question 2: Why is it important to consider the angle between the force and the movement when calculating work? 3. 樂 Question 3: In which practical everyday situations could you apply the concept of net force and work?

Conclusion

Duration: 10 - 15 minutes

The purpose of this stage is to review and consolidate the main concepts covered in the lesson, ensuring that students have a clear and structured view of what they learned. By summarizing the main points, connecting theory with practice, and highlighting the relevance of the topic, the teacher reinforces learning and demonstrates the importance of the acquired knowledge.

Summary

• Definition of net force as the vector sum of all forces acting on an object.
• Method to find net force in different situations.
• Calculation of work done by a force using the formula W = F * d * cos(θ).
• Importance of the angle in the calculation of work, with practical examples.
• Resolution of practical problems involving net force and work.

The lesson connected theory with practice by demonstrating how to calculate net force and the work done by it through practical examples and solved problems. This allowed students to visualize the direct application of theoretical concepts in real situations, facilitating understanding and retention of content.

The study of net force and work is essential for understanding and predicting the behavior of objects in motion, both in everyday situations and in technological applications. For example, engineers use these concepts to design safe and efficient structures such as bridges and buildings, and to develop machines and vehicles that operate optimally.