Simple Machines in Daily Life
AdvancedLevers, pulleys, inclined planes and wheel-and-axles change the size or direction of a force so work becomes easier. Mechanical control is simple and reliable; electronic and pneumatic controls have their own strengths and limits.
- Simple machines change the size or direction of a force but create no energy
- A lever has fulcrum, load and effort — and comes in three classes
- Fixed pulleys change direction, movable ones save force; inclines, wedges and screws trade distance for force
文體小知識：科技知識說明文講解簡單機械的原理和應用，配合生活實例，說明工具如何幫人省力做事。
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1Loads too heavy to move, caps too tight to open, gates too stiff to push — people have always turned to simple machines. A simple machine is the most basic force-transmitting device: it creates no energy, but changes the size or direction of a force so work becomes easier. The Egyptians hauled stones for the pyramids on ramps with levers, and drawing water from a well with a pulley works the same way. Master simple machines and you hold the principle behind most tools and machines.
2A lever is a rigid bar turning on a fulcrum, made of three elements: fulcrum, load and effort. The farther the effort sits from the fulcrum, the less force is needed, which is why prising a jar lid with a long-handled spoon beats using fingers. Levers come in three classes by fulcrum position: scissors, with the fulcrum in the middle, are class one; a wheelbarrow, with the load in the middle, is class two; tweezers, with the effort in the middle, are class three — each suits different jobs.
3Pulleys change the direction of pull or save force: the fixed pulley at the top of a flagpole lets you pull down to raise the flag, while a movable pulley travels with the load and halves the effort. An inclined plane trades a longer distance for a smaller force — stairs and ramps are inclined planes. A wheel and axle turns a large wheel to drive a small shaft, as in door handles and bicycle pedals. A wedge is two inclined planes back to back, which knives and axes use to split things; a screw is an inclined plane rolled up, tightening screws and jar lids alike.
4Simple machines are mechanical control: simple in structure, reliable, durable and needing no power, but limited in force and precision. Electronic and pneumatic control can automate and adjust precisely, yet need electricity or compressed air and are more complex to build and maintain. Choose by need: a hand pump is simple and dependable, an automatic sliding door is quick and hygienic, and bus doors run pneumatically for strength. For example, a manual can opener at home is mechanical, while an electric glass door in a mall is electronic control — each doing what it does best.
1Summary 重點摘要
Levers, pulleys, inclined planes and wheel-and-axles change the size or direction of a force so work becomes easier. Mechanical control is simple and reliable; electronic and pneumatic controls have their own strengths and limits.
2Vocabulary cards Vocabulary
A basic device that changes the size or direction of a force.
A rigid bar turning on a fulcrum to save force or change its direction.
The fixed point about which a lever turns.
The force the user applies to the machine.
The weight a machine must move or lift.
A grooved wheel with a rope that changes pull direction or saves force.
A slope trading a longer distance for a smaller force.
A device where a large wheel turns a small axle to magnify force.
How many times a machine reduces the effort — the load divided by the effort.
Control relying purely on mechanical parts.
3Step by step Steps
- What simple machines meanSimple machines — lever, pulley, inclined plane, wheel and axle, wedge and screw — are the most basic force-transmitting devices. They create no energy: what is saved in force is paid back in distance, a matter of conservation of energy. Their value lies in magnifying a force or changing its direction, making tasks impossible by muscle alone feasible. For example, porters roll a refrigerator up a plank into a lorry: the path is longer, but the force needed is far smaller — the saving of the inclined plane.
- The three elements of a leverA lever consists of a fulcrum, a load and an effort. The fulcrum is the fixed point about which the bar turns, the load is the weight to overcome, and the effort is the force you apply. The longer the effort arm and the shorter the load arm, the less force is needed. For example, with a long-handled bottle opener, the handle is the effort arm, the lid's edge is the fulcrum, and the resistance is the load; garden shears' long handles cut thick branches easily. Find the fulcrum and the two arms and any lever can be analysed.
- Three classes of leversBy the arrangement of the three elements, levers come in three classes. Class one has the fulcrum in the middle — scissors and seesaws — saving force or changing direction. Class two has the load in the middle — wheelbarrows and can openers — always saving force. Class three has the effort in the middle — tweezers and brooms — spending more force but gaining speed and range. For example, in a wheelbarrow the soil sits near the wheel to shorten the load arm, while with a broom the front hand is the fulcrum and the rear hand applies the effort for wide, fast strokes.
- Pulleys and the wheel and axleA fixed pulley is anchored to its frame and only changes the direction of pull without saving force; a movable pulley travels with the load and theoretically halves the effort; pulley blocks combine several for greater savings. The wheel and axle pairs a large wheel with a small shaft: turning the big wheel yields a larger twisting force at the axle. For example, raising a flag by pulling down uses a fixed pulley; furniture hoists use blocks for real savings; door handles and screwdriver grips are wheel-and-axles — the wider the grip, the easier the turn.
- Inclined plane, wedge and screwAn inclined plane trades distance for force — the gentler the slope, the easier the push. A wedge is two inclined planes back to back, turning a downward blow into sideways splitting. A screw is an inclined plane wrapped around a cylinder: several turns produce a strong clamping force. For example, wheelchair ramps are built long and gentle so users can climb unaided; a chef's knife splits food by the wedge principle; a screw-cap seals after a few turns, and a screw jack lifts a whole car by hand.
- Saving force and mechanical advantageMechanical advantage measures how much a simple machine saves force — the load divided by the effort. An advantage above one saves force, usually at the cost of a longer movement of the effort; below one the machine spends more force but gains precision and speed. For example, a movable pulley's advantage of two doubles the rope you must pull, while tweezers, below one, pick up a fine needle for delicate work. Designing tools means balancing force saving against precision, choosing the machine to suit the job.
- Control systems: strengths, limits, usesSimple machines are mechanical control — simple, reliable, durable, cheap and power-free, but limited in force and precision and hard to automate. Electronic control is precise, flexible and programmable yet needs power and fears damp; pneumatic control is strong and safe yet needs an air supply and maintenance. For example, a hand pump keeps working during a blackout, mall doors open automatically for crowds, and bus doors rebound if they catch a passenger. Choosing the control to suit the setting is the heart of applying systems.
4Diagrams Diagrams
5Worked example Example
Example: Grandma can never open a metal cap on a glass jar. Design a small tool to help her, explaining which simple-machine principles it uses.
- Find the difficulty → the cap is screwed tight, Grandma's grip is weak, and the cap is smooth and small
- Choose principles → enlarge the grip to save force (wheel and axle), add rubber for friction, or lever the cap loose
- Design the tool → a hard-plastic ring grip with anti-slip rubber lining that fits over the cap, with a short side lever
- Explain → the ring enlarges the effective handle (wheel and axle); the rubber stops slipping; the lever gives the palm a longer effort arm
- Answer: Design an anti-slip jar opener: a hard-plastic ring lined with rubber grips the cap, making the effective handle several times wider than the cap itself — the wheel-and-axle principle. A short lever on the side lets the palm press down to loosen the cap first. With two simple machines combined, Grandma opens the jar with a light touch. Simple machines need not be complex: identify that the trouble is weak grip and low friction, choose the right principles, and a tiny tool solves a daily problem.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which class of lever is a wheelbarrow? Why does it save force?
Q2What does the fixed pulley on a flagpole do?
Q3Why are wheelchair ramps built long and gentle?
Q4A screw jack lifts a car by hand. Which simple machine does it use?
Q5Give one daily use each of mechanical and electronic control, with each one's strength.
8Recap Recap
- Simple machines change the size or direction of a force but create no energy
- A lever has fulcrum, load and effort — and comes in three classes
- Fixed pulleys change direction, movable ones save force; inclines, wedges and screws trade distance for force
- Mechanical advantage measures force saving, usually paid back in longer movement
- Mechanical, electronic and pneumatic controls each have strengths and limits — choose by the setting