Contextualization

Friction force is extremely important in our daily lives. It is present when we walk, drive, or even when we slide an object on a surface. Let's focus here on kinetic friction, which adds a bit more complexity but brings along a series of interesting applications.

Kinetic friction is a force that acts when an object is in motion. It occurs between the surfaces of two objects that are in contact and moving relative to each other. The kinetic friction force always acts in the opposite direction of the movement. The rougher the contact surface, the greater the kinetic friction force.

To illustrate the relevance of kinetic friction force, we can mention the example of a car's tires. When we accelerate a car, it is the friction between the tires and the road that allows us to move forward. Without it, the wheels would spin in the same place, making it impossible for the vehicle to move. Another very important application is in brake systems, where kinetic friction force is applied to decrease or completely stop the movement of a vehicle.

In this project, we will investigate the kinetic friction force in a fun and playful way. By applying the concept in everyday situations, the idea is to make the learning of this important physical concept easier and more interesting.

To start studying the topic, we recommend reading the chapter on friction from the book "Fundamentals of Physics" by authors Halliday, Resnick, and Walker. For further online study, we suggest the following sources:

• Static and Kinetic Friction - Khan Academy;
• Kinetic Friction - Brasil Escola;
• Video Lesson on Friction and Dissipative Forces - Física Total.

Shall we get our hands dirty?

Practical Activity: Experimenting with Kinetic Friction Force

Project Objectives

1. Understand and differentiate between kinetic and static friction.
2. Experiment with kinetic friction in practice.
3. Develop a scientific report.

Project Description

Groups will need to conduct an experiment to measure the kinetic friction force between two different materials: wood and plastic. They will use a small wooden block and a flat, smooth plastic surface. The wooden block will be pulled over the plastic surface with different forces, and the students will record the measurements.

Required Materials

• A scale to measure the weight of the wooden block.
• A small wooden block of known weight.
• A flat, smooth plastic surface.
• A dynamometer (instrument to measure force) to pull the wooden block.
• A ruler or measuring tape to measure distance.
• A stopwatch to measure time.

Activity Steps

1. Students should first weigh the wooden block using the scale. Record the weight of the block.
2. Place the wooden block on the plastic surface.
3. Using the dynamometer, pull the wooden block with a constant force. Measure the force used. Record it.
4. While pulling the wooden block, use the stopwatch to measure the time it takes for the block to travel a set distance. Record the time and distance.
5. Repeat steps 3 and 4 increasing the applied force each time.
6. Record the values of force, time, and distance for each attempt.
7. Calculate the kinetic friction force for each attempt.

Students should collaborate to conduct the experiment, each with their responsibilities: who operates the dynamometer, who operates the stopwatch, who records the results, etc.

Project Deliverables

The group must submit a written scientific report based on the experiment conducted. In the report, students should contextualize the topic, explain the theory behind kinetic friction force, describe the activity in detail, present the results obtained, and discuss these results.

The four main topics of the report should be:

1. Introduction: Should contextualize kinetic friction force, its relevance and application in the real world, and predict what is expected from the experiment results.
2. Development: Should contain a detailed description of the experiment, the theory behind kinetic friction force, the methodology used, and the results obtained.
3. Conclusions: Should summarize the main points of the experiment and discuss the results, comparing them with the initial prediction and with the theory. It should also explain the learnings obtained.
4. Bibliography: Should indicate the sources used to elaborate the theory and methodology of the experiment.

The report should have a scientific approach but in a way that is understandable for first-year high school students.

Time allocation for the project:

• Experiment: 2 hours
• Report writing: 2 hours

The report submission deadline is one week after the experiment is conducted.