Lesson 3: Simple Machine and Compound Machine

Quick Tip to Remember:

Learning Objectives:

I. Apply concepts of translational and rotational motion to design and build prototypes of efficient, simple, and compound machines;

II. Explain the characteristics of efficient, simple, and compound machines.


SIMPLE MACHINE

A simple machine has few or no moving parts, makes work easier, and REQUIRES LESS FORCE.


1. LEVER

A lever is a board or rigid bar (like a stick or rod) that rests on a support called a fulcrum.

A lever can be used to lift or move things.


2. Wheel and Axle

A circular object (wheel) attached to a smaller rod (axle).

Turning one makes the other turn, reducing effort to move or rotate objects.

Motion:

Angular: The wheel spins around its axis.

Linear: The spinning wheel makes the car move forward, or turning a screwdriver pushes a screw in linearly.


3. Pulley

A wheel with a rope or cable used to lift or pull loads.

Motion:

Angular: Pulley wheel rotates.

Linear: Rope and load move up or down, lifting the load in a straight line.


4. Inclined Plane

A slanted surface that makes it easier to move objects up or down.

Motion:

Mostly linear motion: Objects move up or down the ramp in a straight path.

Angular motion is not involved here unless wheels or rollers are added.


5. Wedge

A wedge is a double inclined plane.

A tool with a sharp edge that splits or cuts objects.

It can be used to push two things apart, lift up an object, or hold an object in place.

Motion:

Linear motion: When you push the wedge down.

Force applied creates separation in the material along a straight line.


6. Screw

A spiral-shaped tool (inclined plane wrapped around a rod) used to hold things together or lift objects.

The threads of the screw make it easier to turn rotational force (twisting) into linear force (pushing/pulling).

Motion:

Angular motion: You twist/rotate the screw.

Linear motion: The screw moves in or out along a straight path.

Examples:

  1. Jar lids – The ridges that twist and seal.

  2. Bottle caps (like water bottles).

  3. Light bulbs – The threaded base that twists into the socket.

  4. C-clamp or G-clamp – Uses a screw to hold wood or metal tightly.

  5. Car jack screw – Lifts cars when changing tires.

  6. Vise (in workshops) – Holds objects in place by tightening a screw.

  7. Meat grinder / pasta maker – Uses a screw mechanism to push food.

  8. Micrometer – For precise measurement using a screw.

  9. Wood screws, metal screws, bolts – The most common type.

  10. Clothespins with screw springs.

C-clamp
Jar lids
Vise
Bottle caps
Light bulbs
Clothespins
Micrometer
Meat grinder


COMPOUND MACHINE

A compound machine is a tool or device that is made by combining two or more simple machines.

Compound machines mix both motions more clearly.


1. Scissors

Combines levers (handles) and wedges (blades) to cut.

Motion:

Angular: Handles turn.
Linear: Blades cut.


2. Bicycle

Combines wheels, axles, levers, pulleys, and gears to move forward.

Motion:

Angular: Wheels and pedals spin.
Linear: Bike moves forward.


3. Can Opener

Uses a wheel, wedge, and lever to open cans.

Motion:

Angular: Handle turns.
Linear: Blade cuts.


4. Wheelbarrow

Combines a lever (handles) and wheel & axle (front wheel) to carry loads.

Motion:

Angular: Wheel rotates.
Linear: Barrow moves forward.


5. Nutcracker

Uses two levers to squeeze and crack nuts.

Motion:

Angular: Handles rotate.
Linear: Nut gets pressed.


6. Crane

Uses pulleys, wheels, and levers to lift heavy loads.

Motion:

Angular: Pulleys spin.
Linear: Load moves up/down.


7. Screwdriver

Combines a screw and lever handle to fasten screws.

Motion:

Angular: Handle turns.
Linear: Screw moves in/out.


8. Fishing Rod

Combines a lever (rod), pulley (line), and wheel & axle (reel).

Motion:

Angular: Reel turns.
Linear: Line moves in/out.


Simple Machines

The 6 basic tools (lever, pulley, wheel & axle, inclined plane, wedge, screw) make work easier.

Characteristics:

  • Have few or no moving parts.

  • Change the size or direction of force.

  • Make tasks easier, but do not reduce the amount of work.

  • Provide a mechanical advantage (using less effort to move a load).

  • Easy to use and found in daily life.


Compound Machines

Machines made by combining two or more simple machines.

Characteristics:

  • Have two or more simple machines working together.

  • Perform more complex tasks than simple machines.

  • Usually more efficient than using just one simple machine.

  • Found in many tools, appliances, and vehicles we use every day.

  • Can be small (scissors) or large (crane, bicycle).

Examples:

Scissors = lever + wedge

Bicycle = wheel & axle + lever + pulley + gears

Can opener = lever + wedge + wheel & axle


What Makes a Machine Efficient?

A MACHINE IS CONSIDERED EFFICIENT WHEN IT PERFORMS ITS INTENDED TASK WITH LESS WASTED ENERGY OR EFFORT.

REMEMBER:

NO REAL MACHINE IS 100% EFFICIENT.

Some energy is usually lost, often because of friction, sound, heat, or deformation.


Characteristics of an Efficient Machine

1. It reduces the effort needed.

Example:

Using a ramp to move a heavy box into a truck is easier than lifting the box straight up.


2. It uses force effectively.

A bottle opener allows a relatively small effort to produce enough force to remove a tight cap.


3. It reduces unnecessary energy loss.

For example, a bicycle with properly lubricated moving parts experiences less friction than one with dry or poorly maintained parts.


4. It performs its intended task effectively.

A machine should actually accomplish the job it was designed to do.

Example:

A pulley designed to lift a load should be able to lift the load smoothly and safely.


5. It minimizes friction when possible.

Friction is a force that opposes motion when surfaces move against each other.

Some friction is useful, but too much friction can waste energy.

Example:

Bicycle chains need lubrication.

Wheels reduce friction when moving objects.

Bearings help rotating parts move more smoothly.


Efficient Machines

Formula for Efficiency

Efficiency (%) = Work Output/Work Input x 100


Work Input = the energy or effort you put into the machine.

Work Output = the useful work the machine actually does.


Example 1: Scissors

Suppose you apply 50 J (joules) of energy to cut paper. The scissors actually use 40 J to cut (10 J is lost to friction and sound).

Efficiency = 40/50 × 100 =80%

The scissors are 80% efficient, meaning most of your effort is useful, but 20% is wasted.


Example 2: Crane

A crane engine uses 1,000 J of energy.

It lifts a load using 900 J of useful work (100 J is wasted as heat and noise).

Efficiency = 900/1000 × 100 =90%

The crane is 90% efficient, meaning it wastes only a little energy.


Key Idea

No machine is 100% efficient because friction, heat, and sound always waste energy.

The closer the output is to the input, the more efficient the machine is.


Like efficient machines,
we too should learn not to waste our
time and effort on things that don’t
really matter.

Instead, let’s focus our energy on what’s
important — our goals and the people who
truly matter in our lives.