• a) Explain the meaning of energy, work and power in relation to machines.
• b) Demonstrate the transformation of mechanical energy using simple apparatus.
• c) Describe applications of simple machines in making work easier.
• d) Appreciate the applications of machines in day-to-day life.
• e) Recognize and explain the working of machines such as treadmill, elevators, escalators and excavator.

Key Concepts & Definitions

Energy — the ability to do work. SI unit: joule (J). Examples: kinetic energy, potential energy, chemical energy.

Work — when a force moves an object through a distance in the direction of the force. Formula: W = F × d. Unit: J (since N·m = J).

Power — the rate at which work is done or energy is transferred. Formula: P = W / t. Unit: watt (W) where 1 W = 1 J/s.

Machine — a device that helps to transmit or transform force and energy so that work is made easier or faster. Examples: lever, pulley, inclined plane, wheel and axle, screw, wedge, treadmill, elevator, escalator, excavator.

Efficiency — how well a machine converts input energy to useful output energy: η = (useful energy out / energy in) × 100%. Because of friction and heat, η < 100% for real machines.

• Work: W = F × d (joules)
• Kinetic energy: KE = 1/2 m v²
• Gravitational potential energy: PE = m g h
• Power: P = W / t = F × v (if force constant and object moves at velocity v)
• Efficiency: η = (useful energy out / energy in) × 100%
• Mechanical advantage (simple machines): MA = load / effort

Simple machine sketches (visuals)

Transformation of Mechanical Energy — Demonstrations

Mechanical energy commonly transforms between kinetic energy (movement) and gravitational potential energy (height). Real machines also convert energy to heat because of friction.

• Pendulum or toy on ramp: A toy car placed at top of a ramp has high potential energy (PE = mgh). It rolls down and gains kinetic energy (KE = 1/2 mv²). At the bottom PE is lowest and KE highest. Friction converts some energy to heat and sound.
• Mass on a pulley: A mass falling transfers potential energy into kinetic energy of the mass and rope; a motor could convert electrical energy into mechanical energy to lift a mass (reverse).
• Bouncing ball: On impact some kinetic energy becomes elastic potential energy, then back to kinetic; losses show conversion to heat and sound.

How Simple Machines Make Work Easier

Simple machines change the size or direction of the force so you can do the same work with less effort or do work faster. They do not remove the need to do work — they change how the force is applied.

• Lever: Increases force or changes direction, e.g., using a crowbar to lift a heavy stone.
• Pulley: Changes direction of force and multiple pulleys reduce effort, e.g., flagpole or bucket on a well.
• Inclined plane (ramp): Move heavy objects to greater height with less force, e.g., loading a jembe into a truck using a plank.
• Wheel and axle: Reduces friction and effort, e.g., bicycle wheels, wheelbarrow.

Everyday machines — how they use energy, work and power

Treadmill

Converts electrical energy into mechanical energy to move the belt. A person walking uses chemical energy, which becomes mechanical energy. Power rating of treadmill motor tells how quickly it can do work (lift/move person).

Elevators

Use motors (electrical to mechanical energy) and cables to lift people. Work done to lift mass m by height h: W = m g h. Power required depends on time taken to raise the load: P = W / t. Safety brakes and counterweights increase efficiency and reduce motor power needed.

Escalators

Continuous moving staircases; motors do work to lift and lower many people continually. Escalators reduce the force individuals must use to change floors (work is done by the machine).

Excavator

Heavy machine that converts chemical energy from fuel (or electrical energy) into mechanical energy for digging. Uses hydraulic systems and levers to increase force at the bucket — making digging heavy soil possible with manageable controls.

Worked Examples (simple)

Suggested Learning Experiences (Activities & Demonstrations)

These use simple materials often available in Kenyan schools or homes.

1. Toy car on ramp: Measure height and time to demonstrate mgh ↔ 1/2 mv² and energy losses (friction). Discuss sources of lost energy.
2. Pulley lifting: Using rope, bucket and weights (stones, sand in a jerrycan), measure effort with and without additional pulleys to show mechanical advantage.
3. Lever experiment: Use a wooden plank and fulcrum (stone) to lift different loads; measure effort distance and load distance to show moments and MA.
4. Elevator model: Build a small elevator using string, pulley and a simple DC motor or hand crank; measure work done lifting a small mass and power when lifted in different times.
5. Wheelbarrow comparison: Compare pushing a load in a wheelbarrow vs carrying by hand (measure force with spring balance if available) to show reduced effort and faster work.
6. Excavator model: Make a simple hydraulic arm using syringes and tubes to show how hydraulic force multiplies and makes digging easier.
7. Discussion and field visit: Visit a mini construction site or shopping mall to observe elevators, escalators and excavators; note energy sources, safety measures and signs of wear.

Safety, Conservation and Maintenance

• Always use safety gear when doing demonstration (gloves, goggles where needed).
• Machines must be maintained (lubrication reduces friction losses and improves efficiency).
• Conserve energy by using efficient machines and switching off motors when not in use.

Assessment Ideas / Revision Questions

1. Define work, energy and power and give units for each.
2. A porter lifts a 20 kg bag 2 m in 4 s. Calculate the work done and the power developed (g = 9.8 m/s²).
3. Explain how a pulley reduces the effort needed to lift a load. Give a sketch of a 2-pulley system.
4. Describe how an excavator converts energy to do work. Mention at least two energy transformations that occur.
5. Suggest how a school could reduce energy use by changing how machines are used or maintained.

• Use locally available materials (planks, buckets, empty jerrycans, ropes, bicycle wheels) for demonstrations.
• Encourage group work and visits to local workshops, markets or construction sites to see machines in action.