Explain the concept and laws of friction (types of friction, laws of friction)

First law: The frictional force is directly proportional to the normal force between the two surfaces.

$F_f = \mu N$

Where $F_f$ is the frictional force, $N$ is the normal force (equal to weight $mg$ on a horizontal surface), and $\mu$ is the coefficient of friction.

Second law: The frictional force is independent of the apparent area of contact between the surfaces. Whether you slide a brick flat or on its edge, the friction is the same provided the normal force is unchanged.

Third law: The kinetic frictional force is independent of the sliding velocity. Once an object is sliding, the friction acting on it stays constant regardless of how fast it moves.

A wooden block with mass 15 kg rests on a horizontal floor. The coefficient of friction between the block and floor is 0.3. Calculate the force required to just start the block moving.

Solution:

First, find the normal force: $N = mg = 15 \times 10 = 150 \, \text{N}$

Now apply the first law of friction: $F_f = \mu N = 0.3 \times 150 = 45 \, \text{N}$

The minimum force required to overcome limiting friction is 45 N.

In many situations, friction causes unwanted wear, heat, or energy loss. Common methods to reduce friction include:

• Polishing surfaces to make them smoother
• Lubrication with oil or grease to create a slippery layer
• Using ball bearings to convert sliding friction into rolling friction (which is much smaller)
• Streamlining objects like cars to reduce air resistance

In Tanzania, friction is essential when walking on dusty roads in villages like Mwanza or Arusha — the friction between your sandals and the ground prevents you from slipping. When a daladala driver applies brakes to stop at a market in Kariakoo, friction between the brake pads and the wheel converts kinetic energy into heat, slowing the vehicle safely. Understanding friction helps engineers design safer vehicles and more efficient machines used in Tanzanian workplaces.