Frictional force always acts in the direction opposite to the displacement of the sliding object. Since the angle between the force vector and the displacement vector is 180 degrees, the work done (W = Fd cos 180°) is negative, indicating energy dissipation.

Friction is the resistive force that opposes relative motion between two surfaces in contact. A slippery surface, such as ice or a lubricated floor, has a very low coefficient of friction, which significantly reduces the resistive force compared to rougher surfaces, making it difficult for objects to maintain traction.

When vehicle brakes are applied, brake pads are pressed against a rotating disc or drum. The resulting kinetic friction between these surfaces converts the vehicle's kinetic energy into thermal energy, thereby reducing the vehicle's speed. Friction is the resistive force that opposes the relative motion between the surfaces in contact, allowing the vehicle to decelerate and eventually come to a complete stop.

Limiting friction is the maximum value of static friction that comes into play when a body is just on the verge of moving over the surface of another body. Once the applied force exceeds this limiting value, the object begins to move, and kinetic friction takes over.

Lubricants are substances, such as oil or grease, introduced between two surfaces in contact to minimize friction. By creating a thin film that separates the surfaces, they reduce the resistance to motion, thereby decreasing the frictional force.

The force of friction (f) is calculated as f = μN, where μ is the coefficient of friction and N is the normal force. On a horizontal surface, N = mg. Using g = 10 m/s², N = 6 kg * 10 m/s² = 60 N. Thus, f = 0.6 * 60 N = 36 N.

According to Amontons' laws of friction, the frictional force is directly proportional to the normal force pressing the surfaces together. By increasing the pressure or force between the two surfaces, the microscopic contact points between them are forced more firmly together, thereby increasing the resistance to motion.

When a person walks, they push their foot backward against the ground. According to Newton's third law, the ground exerts an equal and opposite force forward on the foot. This forward force is the static friction between the shoe and the ground, which enables locomotion.

Walking is an application of Newton's third law. To move forward, a person must exert a backward force on the ground. Friction between the soles of the shoes and the ground provides the necessary resistance to prevent slipping, allowing the ground to exert an equal and opposite forward reaction force on the person.

Proper tire inflation is critical for vehicle safety and performance. Correct pressure ensures that the tire's contact patch with the road is optimized, which provides the necessary traction to prevent skidding. Additionally, it minimizes rolling resistance, which helps in maintaining control and efficiency during operation.