When the breaks in a car are applied, the frictional force on the tyres is?

Analysis

This question tests your understanding of friction and its role in daily mechanics, specifically regarding vehicle safety and control.

Concept Explanation

Friction is a force that opposes the relative motion between two surfaces in contact. In the context of a moving car:

1. The Role of Friction: When you apply the brakes, the brake pads grip the wheels, and the tyres grip the road. This creates a frictional force between the tyres and the road surface.
2. Direction: Because friction always acts to oppose motion, the frictional force generated by the road on the tyres acts in the opposite direction to the car's velocity.
3. Advantage vs. Disadvantage: In this specific scenario, this force is an advantage. Without this opposing frictional force, the car would not be able to decelerate or come to a stop. It is the force that allows the car to lose kinetic energy and eventually stop safely.

Step-by-Step Solution

1. Identify the goal: The goal of applying brakes is to stop the car.
2. Determine the force direction: To stop a forward-moving object, a force must be applied in the backward direction (opposite to the motion). Friction provides this force.
3. Evaluate the nature of the force: Since the force achieves the desired outcome (stopping the car), it is classified as an advantage.
4. Conclusion: The frictional force is an advantage because it acts in the opposite direction of the motion, effectively reducing the car's speed.

Exam Strategy Tip

Whenever you encounter questions about friction in exams, ask yourself: "Is this friction helping me achieve the intended motion or stop it?"

• If it helps you move (like walking or a car accelerating), it is an advantage.
• If it helps you stop (like braking), it is also an advantage.
• If it causes unwanted wear and tear or heat (like in an engine), it is a disadvantage.