FORCE AND ENERGY Notes, Quizzes & Revision
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Context: examples and local references are Kenyan (e.g., Olkaria geothermal, Turkana wind, hydropower, jikos and matatus).
Overview
"Force" is a push or pull that can change an object's motion or shape. "Energy" is the ability to do work or cause change. In everyday Kenyan life, forces move matatus, bicycles and seeds; energy lights homes, cooks food and runs factories.
Key concepts and definitions
- Force (F) β a push or pull measured in newtons (N). It can change speed, direction, or shape.
- Energy β ability to do work. Common forms: kinetic (moving objects), potential (stored), thermal, chemical, electrical, nuclear, and renewable sources (solar, wind, hydro, geothermal).
- Work (W) β when a force causes displacement: W = F Γ s (force Γ distance in direction of force). Unit: joule (J).
- Power (P) β rate of doing work: P = W / t. Unit: watt (W) (1 W = 1 J/s).
- Conservation of energy β energy cannot be created or destroyed; it changes form (e.g., chemical energy in wood β thermal energy when burned).
Common symbols and units
F (force) β newton (N) | m (mass) β kilogram (kg) | a (acceleration) β m/sΒ²
W (work) β joule (J) | E (energy) β J | P (power) β watt (W) | g (gravity) β 9.8 m/sΒ² on Earth
Important formulas (with short notes)
- Newton's 2nd law: F = m Γ a. (Force equals mass times acceleration.)
- Weight: Wt = m Γ g. (Weight is the force due to gravity.)
- Work: W = F Γ s Γ cosΞΈ. (If force is in same direction as movement, cosΞΈ = 1.)
- Kinetic energy: KE = 1/2 Γ m Γ vΒ². (Energy of motion.)
- Gravitational potential energy: PE = m Γ g Γ h. (Energy due to height.)
- Power: P = W / t or P = F Γ v (force Γ velocity when force and speed constant).
Simple visual: block on an incline (forces shown)
On an incline the weight can be split into components: down-slope component mg sinΞΈ (causes motion) and perpendicular mg cosΞΈ (balances normal). Friction opposes motion.
Everyday Kenyan examples
- Matatu brakes: friction between brake pads and wheels turns kinetic energy into thermal energy (heat).
- Olkaria geothermal power: geothermal energy (heat under ground) converted to electrical energy for homes.
- Solar panels on homes: sunlight (radiant energy) β electrical energy to run lights and radios.
- Turkana wind farms: kinetic energy of wind β electrical energy by turbines.
- Cooking on a jiko: chemical energy in charcoal β thermal energy to cook food.
Worked problems (step-by-step)
Simple demos to observe concepts
- Push a ruler off a table and watch acceleration β discuss F = ma and role of mass.
- Roll two balls (different masses) down the same slope β compare speeds and kinetic energy.
- Use a spring scale to measure weight of objects and compute mass using g β 9.8 m/sΒ² (mass = weight/g).
Common misconceptions
- Energy is not a "thing" you can touch β it is a property that objects have which allows work to be done.
- Force is not the same as pressure. Pressure = force / area.
- Objects at rest still have potential energy if placed at a height.
Quick revision & practice
- Define force and give two Kenyan examples.
- Write formulae for kinetic and potential energy and state their units.
- Calculate the work done when a force of 50 N moves a crate 4 m along the floor.
- Explain briefly how energy changes when a matatu brakes to a stop.
Glossary & Summary
Glossary: Force β push/pull; Work β force Γ distance; Energy β ability to do work; Power β work per time.
Summary: Forces change motion or shape; energy exists in many forms and is conserved. Use the formulas above to solve routine problems. Relate ideas to Kenyan examples (transport, power plants, cooking) to make learning local and practical.