Grade 10 physics Mechanics and Thermal Physics – Energy, Work, Power and Machines Notes

1.6 Energy, Work, Power and Machines

Topic: 1.0 Mechanics and Thermal Physics — Subject: Physics — Target age: 15 (Kenya)

Specific learning outcomes (By the end of the sub-strand the learner should be able to):

1. a) Explain the meaning of energy, work and power in relation to machines.
2. b) Demonstrate the transformation of mechanical energy using simple apparatus.
3. c) Describe applications of simple machines in making work easier.
4. d) Appreciate the applications of machines in day-to-day life.
5. e) Describe and give examples of machines (including treadmill, elevators, escalators, excavator).

Key concepts and definitions

• Energy: the ability to do work. SI unit: joule (J).
• Kinetic energy (KE): energy of motion, KE = 1/2 mv² (m in kg, v in m/s).
• Gravitational potential energy (PE): energy due to height, PE = m g h (g ≈ 9.8 m/s²).
• Work (W): when a force causes displacement. W = F s cosθ. SI unit: joule (J).
• Power (P): rate at which work is done. P = W / t. SI unit: watt (W) = J/s.
• Machine: device that helps transfer or transform energy and/or reduce effort needed to do work.
• Simple machines: lever, pulley, wheel & axle, inclined plane, wedge, screw — they change magnitude or direction of forces.
• Efficiency: useful energy out ÷ energy in × 100% (accounts for losses like friction).

Simple worked example

A labourer lifts a 50 kg crate vertically by 2.0 m in 5.0 s. How much work is done? What power is required?

Transformation of mechanical energy — classroom demonstrations

1. Ball on an inclined plane (PE → KE)

Apparatus: wooden plank as ramp, metre rule, small ball, stopwatch, mass (optional).

Procedure: raise one end of the plank by a known height h, release the ball from rest at the top and measure its speed at the bottom (or time taken to travel known distance).

What to observe & calculate: initial PE = m g h; final KE ≈ 1/2 m v². Compare PE and KE to show transformation and note energy losses (friction, sound).

2. Pendulum (PE ↔ KE)

Use a simple pendulum: pull bob to one side and release. Observe highest and lowest points: energy swaps between PE and KE. Measure amplitude decay to discuss energy loss (air resistance/friction).

3. Lever with weights (force advantage)

Set up a plank on a fulcrum, place weights at different distances. Show how a smaller force can lift a larger load when applied further from the fulcrum (mechanical advantage).

Simple machines and Kenyan everyday examples

• Lever — seesaw at school, crowbar to open a crate, hoe handle used in farms: changes size and direction of effort.
• Pulley — lifting water from wells, flagpoles, cranes at construction sites.
• Wheel and axle — bicycles (common transport), cart wheels, door knobs.
• Inclined plane (ramp) — wheelchair ramps in public buildings, ramps used to load goods onto vehicles.
• Wedge — machete used in farming to cut sugarcane, axe to split firewood.
• Screw — jar lids, vices used in workshops.

Machines in daily life — treadmill, elevators, escalators, excavator

• Treadmill: electrical energy → mechanical energy (motor turns belt). Used for exercise and physiotherapy. Demonstrate measuring power by noting a person’s weight, speed and incline (use formulas to estimate work done).
• Elevator (lift): electric motor does work lifting the cabin against gravity: electrical energy → mechanical work (PE increase). Common in malls and tall buildings in Nairobi and other cities.
• Escalator: a moving staircase: electrical energy drives belts and steps; makes movement between floors easier for many people at once.
• Excavator: diesel/electric engine provides energy to move arms, bucket and tracks: chemical energy → mechanical energy. Widely used in construction (roads, building sites) and in digging irrigation canals on farms.

Suggested learning experiences (practical, interactive and field-based)

1. Hands-on experiments (class groups):
   • Ball on ramp: measure heights and speeds; compute PE and KE and estimate energy lost to friction.
   • Lever experiment: vary distances of load and effort; calculate mechanical advantage and relate to work done.
   • Pulley systems: compare single pulley and block-and-tackle; measure force needed to lift same load.
2. Measurement tasks:
   • Time a student climbing a flight of stairs and compute work done lifting their body; calculate power output (encourages direct measurement and calculation).
3. Field visit / observation:
   • Visit a construction site (observe excavators) or a shopping mall (observe elevators & escalators). Learners note energy sources, safety measures and how machines reduce effort.
4. Project work:
   • Design and build a simple machine model (e.g., a lever-based lifting device or a small pulley system). Present how it reduces effort and compute mechanical advantage.
5. Group discussion & reflection:
   • Discuss pros and cons of machines in daily life (time-saving, energy consumption, maintenance costs, job impacts).

Safety and classroom management

• Use eye protection for experiments with moving parts. Keep hands away from pulleys and belts in motion.
• Secure heavy masses on levers and supports to prevent sudden slips. Supervise field visits and follow site safety rules (helmets, high-visibility vests at construction sites).

Assessment ideas (formative and summative)

• Short calculations: compute work and power in given situations (lifting, pushing, walking uphill).
• Practical test: set up a ramp experiment and report PE→KE results and % energy lost.
• Project presentation: model of a simple machine showing mechanical advantage and explanation of daily application.
• Short answer: explain how an escalator or excavator transforms energy and makes work easier.

Summary

Energy is the ability to do work. Machines change how force is applied and how energy is transformed so that tasks become easier, faster or possible. By using experiments (ramps, levers, pulleys) students see energy transformations and learn to calculate work, power and efficiency. Relating lessons to local machines (treadmills in gyms, elevators in malls, escalators at airports, excavators at construction sites) helps learners appreciate the physics and the social value of machines.

Glossary (quick)

• Work: force × displacement in direction of force.
• Power: rate of doing work.
• Mechanical advantage: ratio of load force to effort force for a machine.
• Efficiency: useful output energy ÷ input energy × 100%.

Prepared for Kenyan learners aged 15 — these notes can be used alongside demonstrations, practicals and local field visits (construction sites, malls, gym/physiotherapy centres) to give learners strong connections between physics and everyday life.