1.6 Energy, Work, Power and Machines

• Kinetic energy, potential energy (elastic and gravitational) and the law of conservation of energy
• Work and power
• Machines: levers, inclined plane, pulleys, wheel and axle, gears, hydraulic lift, pulley belt, the screw
• Mechanical advantage, velocity ratio and efficiency
• Applications of machines, including treadmills, elevators, escalators and excavators

• explain the meaning of energy, work, power and machines as used in physics
• demonstrate the transformation of mechanical energy using simple apparatus
• apply mathematical relationships involving kinetic energy, potential energy, work and power
• determine mechanical advantage, velocity ratio and efficiency of simple machines
• describe applications of simple machines in making work easier
• appreciate the applications of machines in day-to-day life

“How do machines make work easier?”

“Where does the energy of a swinging pendulum go at the top of each swing?”

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1. Work and energy
   40 min · 2 practice tasks · quiz
   What physics counts as work, the two forms of mechanical energy, and why the total never changes.
2. Power, and what a machine actually does
   40 min · 2 practice tasks · quiz
   How fast work is done, and the three numbers that describe every machine.
3. The simple machines
   40 min · 2 practice tasks · quiz
   Levers, pulleys, inclined planes, screws, gears and hydraulics - and how to find the velocity ratio of each.
4. Forms of energy and how they change
   40 min · 1 practice tasks · quiz
   Name the common forms of energy, trace Kenyan transformation chains, and keep the total the same.
5. Work when the force is at an angle
   40 min · 1 practice tasks · quiz
   Only the component of force along the motion counts: W = F d cos θ.
6. Kinetic energy and the square of speed
   40 min · 1 practice tasks · quiz
   Derive K.E. = ½ m v² from work, then use it on Kenyan vehicles and falling objects.
7. Gravitational potential energy
   40 min · 1 practice tasks · quiz
   P.E. = m g h is the work stored by raising a mass, from a sack onto a shelf to water behind a dam.
8. Elastic potential energy
   40 min · 1 practice tasks · quiz
   A stretched spring or catapult stores work as ½ F e or ½ k e², then gives it back as kinetic energy.
9. Conserving mechanical energy
   40 min · 1 practice tasks · quiz
   P.E. + K.E. stays constant when friction is negligible; a pendulum, a thrown ball and a catapult show the trade.
10. Power in practice
    40 min · 1 practice tasks · quiz
    P = W/t and P = F v, human power on stairs, motors, and why a KPLC bill is in kilowatt hours.
11. Three classes of levers
    40 min · 1 practice tasks · quiz
    Class is named by what sits in the middle. Kenya tools: crowbar, wheelbarrow, forearm, borehole pump.
12. Pulley systems
    40 min · 1 practice tasks · quiz
    Count supporting strings for V.R. Fixed pulleys turn the effort; movable pulleys share the load.
13. The inclined plane and the screw
    40 min · 1 practice tasks · quiz
    A ramp trades a longer path for a smaller effort; a screw is that ramp wrapped around a cylinder.
14. Wheel and axle, gears and pulley belts
    40 min · 1 practice tasks · quiz
    A large wheel turns a small axle; gears trade teeth; a belt copies rotation to another shaft.
15. Hydraulic machines
    40 min · 1 practice tasks · quiz
    Pressure is the same throughout a liquid, so a small effort piston can raise a large load piston.
16. Measuring M.A., V.R. and efficiency
    40 min · 1 practice tasks · quiz
    A pulley-block practical: record load, effort and both distances, then compute the three numbers.
17. Efficiency, friction and a heavier load
    40 min · 1 practice tasks · quiz
    Why efficiency is always under 100%, why it often rises with load, and how oiling and design help.
18. Machines around Kenya
    40 min · 1 practice tasks · quiz
    Elevators, escalators, excavators, treadmills and local builds: name the simple machines inside and construct one.