Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define friction and identify its types (static, kinetic, rolling).
• Explain factors affecting friction (surface roughness, applied force, temperature).
• Describe the purpose and benefits of lubrication.
• Identify different types of lubricants and their applications.
• Explain methods of applying lubrication.

Lesson summary

Friction and lubrication are fundamental concepts in Mechanical Technology. Understanding these principles is essential for anyone working with machines, engines, or any system involving moving parts. In South Africa, where industries like mining, agriculture, and manufacturing are vital, a solid grasp of friction and lubrication contributes directly to efficient operation, reduced wear and tear on equipment, and ultimately, economic productivity. From the gearbox in a bakkie driving through the Karoo to the massive crushers used in a platinum mine, friction and lubrication play a crucial role. Poor maintenance and lubrication can lead to breakdowns, costly repairs, and even safety hazards.

Lesson notes

2.1 Friction: Friction is a force that opposes motion when two surfaces are in contact and moving relative to each other. It's a ubiquitous force that can be both beneficial and detrimental. Without friction, we wouldn't be able to walk, drive, or hold objects securely.

However, friction also causes wear, generates heat, and reduces efficiency in mechanical systems.

There are three main types of friction: Static Friction: This is the force that prevents an object from starting to move when a force is applied to it. Static friction is always equal and opposite to the applied force, up to a maximum value. Think about pushing a heavy fridge across a tiled floor. Initially, a large force is needed to overcome static friction and get it moving. The formula for maximum static friction is: F s(max) = μ s * N Where: F s(max) is the maximum static friction force μ s is the coefficient of static friction (a dimensionless value that depends on the nature of the two surfaces) N is the normal force (the force pressing the two surfaces together)

Kinetic Friction: This is the force that opposes the motion of an object that is already moving. Kinetic friction is generally less than static friction. Once the fridge is moving, it's easier to keep it moving because you only need to overcome kinetic friction.

The formula for kinetic friction is: F k = μ k * N Where: F k is the kinetic friction force μ k is the coefficient of kinetic friction (also a dimensionless value)

N is the normal force Rolling Friction: This is the friction force that opposes the motion of a rolling object. Rolling friction is typically much less than static or kinetic friction. This is why it's easier to move heavy objects on wheels. Consider a wheelbarrow loaded with bricks. It's much easier to push than dragging the bricks directly on the ground because rolling friction is minimized. Rolling friction is complex but depends on the deformation of the rolling object and the surface it's rolling on.

Factors Affecting Friction: Surface Roughness: Rougher surfaces have a higher coefficient of friction. This is because the irregularities on the surfaces interlock, increasing the force required to overcome friction.

Applied Force (Normal Force): The greater the force pressing the surfaces together, the greater the friction. This is directly reflected in the formulas for friction, where friction is proportional to the normal force.

Temperature: Temperature can affect the coefficient of friction. In some cases, higher temperatures can reduce friction (e.g., lubricating oils become less viscous). In other cases, higher temperatures can increase friction (e.g., due to oxidation or softening of materials).