Simple Machines

Simple Machines

Middle School

​

Learning Objectives

• Define a simple machine and describe how it makes work much easier.

• Identify and describe the six main types of simple machines.

• Understand the important scientific concepts of force, work, friction, and efficiency.

• Differentiate between simple and compound machines and provide examples of each.

• Explain different ways to increase the efficiency of various simple machines.

Key Vocabulary

​

Force

A push or pull acting on an object. The standard unit of measurement for force is newtons (N).

​

Work

Work is done when a force is applied to an object, causing it to move over a distance.

​

Simple Machine

A basic mechanical device with few or no moving parts that makes doing work easier by reducing force.

​

Lever

A stiff rod that pivots around a fixed point, called a fulcrum, to lift or move loads.

​

Pulley

A simple machine that uses a wheel and rope to lift, lower, or move heavy objects with ease.

​

Wedge

A tool composed of two inclined planes, used to separate two objects or portions of an object.

Key Vocabulary

​

Wheel and Axle

A wheel is locked to a central axle, and they rotate together when force is applied.

​

Inclined Plane

An inclined plane is a slope or ramp that makes lifting objects easier by increasing the distance.

​

Screw

A screw is a simple machine made by wrapping an inclined plane in a spiral around a post.

​

Friction

Friction is a force that holds back the motion of sliding objects, reducing a machine's efficiency.

​

Fulcrum

The fulcrum is the fixed point on which a lever pivots or is supported to lift a load.

​

​

What Are Force, Work, and Simple Machines?

• A force is a push or pull on an object, measured in newtons (N).

• Work is done only when a force moves an object over a distance.

• If the object does not move, no work is done, no matter what.

• Simple machines make work easier by reducing the amount of force you need.

​

Multiple Choice

Which of the following best defines a force?

• The amount of matter that makes up an object.

• A push or a pull on an object.

• The speed at which an object is moving.

• The energy an object has due to its motion.

Multiple Choice

In which of the following scenarios is work being done on an object?

• A wall stands still while the wind blows against it.

• A person holds a heavy box without moving.

• A person pushes a cart, and it rolls across the floor.

• A car is parked on a flat street.

Multiple Choice

A student pushes against a heavy door, but the door does not move. Which statement best explains why no work is done on the door?

• Work is only done when an object is pulled, not pushed.

• No work is done because the door did not move over a distance.

• The force applied by the student is not measured in newtons.

• The student is not applying enough force to the door.

​

​

The Six Types of Simple Machines

• Lever: A stiff bar that rests on a support called a fulcrum.

• Inclined Plane: A flat surface set at an angle, like a ramp.

• Wedge: Two inclined planes joined back-to-back to split or separate objects.

• Screw: An inclined plane that is wrapped around a rod or cylinder.

• Wheel and Axle: A wheel with a rod through its center that moves together.

• Pulley: A wheel with a groove that a rope fits into to lift things.

Multiple Choice

Which simple machine is defined as a stiff bar that rests on a support called a fulcrum?

• Wedge

• Screw

• Lever

• Pulley

Multiple Choice

Which two simple machines are described as being variations of an inclined plane?

• A wheel and axle and a lever

• A wedge and a screw

• A lever and a pulley

• A pulley and a wedge

Multiple Choice

A device is built to lift a heavy bucket. It uses a wheel that has a rope in a groove, and the wheel spins on a rod that passes through its center. Which two simple machines have been combined in this device?

• An inclined plane and a screw

• A lever and a wedge

• A wheel and axle and a pulley

• A screw and a pulley

Examples of Compound Machines

​

Wheelbarrow

• A wheelbarrow is a compound machine used to move heavy loads easily.

• It combines a lever with a wheel and axle to work together.

• This combination makes lifting and carrying materials much less difficult for you.

​

Scissors

• Scissors are a compound machine that is designed for the task of cutting.

• They are made of two levers that have been joined at a pivot.

• The blades also act as wedges to separate the material being cut.

​

Bicycle

• A bicycle is a more complex compound machine that is used for transportation.

• It uses levers for handlebars, and includes multiple wheels and axles.

• The gears and chain act as pulleys to help transfer power efficiently.

Multiple Choice

What makes a machine like a wheelbarrow or scissors a 'compound machine'?

• It is designed for a single, specific task.

• It can be used to move heavy loads.

• It is more complex and difficult to use.

• It is made by combining two or more simple machines.

Multiple Choice

How do the simple machines within a pair of scissors work together to cut something?

• A pulley lifts the blades, and a wedge holds the material.

• Two levers are joined to provide force, and the blades act as wedges to separate material.

• A wheel and axle spins the blades, and a lever pushes them forward.

• A gear turns the blades, and a screw holds them together.

Multiple Choice

A wheelbarrow and a bicycle are both used for movement. Based on their descriptions, what simple machines do they both use to perform their function?

• A lever and a wheel and axle

• A wedge and a lever

• Pulleys and screws

• Gears and wedges

​

​

Efficiency and Friction

• Mechanical efficiency measures how a machine converts input work to useful output work.

• No machine can be 100% efficient in the real world because of friction.

• Friction is a force that resists motion and turns some work into heat.

• Using lubricants like oil reduces friction and therefore increases the machine's efficiency.

​

Multiple Choice

What does a machine's mechanical efficiency measure?

• How well it converts input work into useful output work

• The amount of heat the machine produces

• The total amount of energy it can create

• How quickly the machine can complete a task

Multiple Choice

What is the relationship between friction and the efficiency of a machine?

• Friction only affects the speed of a machine, not its efficiency.

• Friction has no effect on a machine's efficiency.

• Friction decreases a machine's efficiency by converting useful work into heat.

• Friction increases a machine's efficiency by creating heat.

Multiple Choice

A student adds oil to the chain of a bicycle, making it easier to pedal. What is the best explanation for why this happens?

• The oil converts heat from the chain back into useful work.

• The oil increases the amount of input work from the pedals.

• The oil reduces friction in the chain, which increases the bicycle's efficiency.

• The oil increases the bicycle's mass, making it move faster.

How to Increase Machine Efficiency

​

Levers

• Using a fulcrum with a sharp point reduces the area of contact.

• A more rigid bar ensures that no effort is wasted bending it.

• An oiled hinge at the fulcrum point will greatly reduce any friction.

​

Pulleys

• A grooved wheel helps to guide the rope and keep it in place.

• Lubricating the axle of the wheel allows it to spin more freely.

• Using a cable that grips the wheel ensures that it will not slip.

​

Inclined Planes

• You can use an inclined plane that has a much smoother surface.

• Applying a lubricant to the ramp's surface also increases the overall efficiency.

• Keeping the ramp clean and free of debris also helps reduce friction.

Multiple Choice

What is the primary purpose of applying oil to a lever's hinge or lubricant to a pulley's axle?

• To prevent the parts from bending under pressure.

• To increase the area of contact between parts.

• To reduce the force of friction between moving parts.

• To ensure that ropes or cables do not slip.

Multiple Choice

How do using a more rigid bar for a lever and a cable that grips a pulley wheel both increase a machine's efficiency?

• They both require a lubricant to function properly.

• They both increase the machine's overall weight and stability.

• They both work by reducing friction between the machine's moving parts.

• They both ensure that effort is not wasted through bending or slipping.

Multiple Choice

A team builds a machine using a lever on a fulcrum and a pulley with a rope. They find that the lever's fulcrum scrapes roughly and the rope keeps jumping off the pulley wheel. Which combination of improvements would best solve these specific problems?

• Oiling the fulcrum and using a much heavier pulley wheel.

• Using a more flexible bar and a smoother rope.

• Using a sharper fulcrum and a pulley wheel with a groove.

• Making the lever bar longer and the rope thicker.

​

Common Misconceptions

Misconception	Correction
Simple machines reduce the amount of work you have to do.	Machines reduce the force needed, not the total work done.
A machine can be 100% efficient.	This is impossible because friction always converts some work into heat.
A shorter ramp is always more efficient.	Steeper ramps require more force. Efficiency depends on reducing friction, not just length.

​

Summary

• Simple machines reduce the force needed, often by increasing the distance.

• The six simple machines are the lever, pulley, wheel and axle, inclined plane, wedge, and screw.

• Compound machines are formed by combining two or more simple machines.

• Friction is a force that opposes motion, preventing any machine from being 100% efficient.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4