What is a perpetual motion machine?

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90 min
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1

Think about these questions before watching.

  1. What comes to mind when you hear the phrase 'perpetual motion'?
  2. What are some common sources of energy that power the machines and devices we use every day?
2

Watch the video carefully. Pay attention to the main ideas and key details.

Video script87 segments · click a timestamp to jump

Around 1159 A.D.,

a mathematician called Bhaskara the Learned

sketched a design for a wheel containing curved reservoirs of mercury.

He reasoned that as the wheels spun,

the mercury would flow to the bottom of each reservoir,

leaving one side of the wheel perpetually heavier than the other.

The imbalance would keep the wheel turning forever.

Bhaskara's drawing was one of the earliest designs

for a perpetual motion machine,

a device that can do work indefinitely without any external energy source.

Imagine a windmill that produced the breeze it needed to keep rotating.

Or a lightbulb whose glow provided its own electricity.

These devices have captured many inventors' imaginations

because they could transform our relationship with energy.

For example, if you could build a perpetual motion machine

that included humans as part of its perfectly efficient system,

it could sustain life indefinitely.

There's just one problem.

They don't work.

Ideas for perpetual motion machines

all violate one or more fundamental laws of thermodynamics,

the branch of physics that describes the relationship

between different forms of energy.

The first law of thermodynamics says that energy can't be created or destroyed.

You can't get out more energy than you put in.

That rules out a useful perpetual motion machine right away

because a machine could only ever produce as much energy as it consumed.

There wouldn't be any left over to power a car or charge a phone.

But what if you just wanted the machine to keep itself moving?

Inventors have proposed plenty of ideas.

Several of these have been variations on Bhaskara's over-balanced wheel

with rolling balls or weights on swinging arms.

None of them work.

The moving parts that make one side of the wheel heavier

also shift its center of mass downward below the axle.

With a low center of mass,

the wheel just swings back and forth like a pendulum,

then stops.

What about a different approach?

In the 17th century, Robert Boyle came up with an idea

for a self-watering pot.

He theorized that capillary action,

the attraction between liquids and surfaces

that pulls water through thin tubes,

might keep the water cycling around the bowl.

But if the capillary action is strong enough to overcome gravity

and draw the water up,

it would also prevent it from falling back into the bowl.

Then there are versions with magnets, like this set of ramps.

The ball is supposed to be pulled upwards by the magnet at the top,

fall back down through the hole,

and repeat the cycle.

This one fails because like the self-watering pot,

the magnet would simply hold the ball at the top.

Even if it somehow did keep moving,

the magnet's strength would degrade over time

and eventually stop working.

For each of these machines to keep moving,

they'd have to create some extra energy

to nudge the system past its stopping point,

breaking the first law of thermodynamics.

There are ones that seem to keep going,

but in reality, they invariably turn out to be drawing energy

from some external source.

Even if engineers could somehow design a machine

that didn't violate the first law of thermodynamics,

it still wouldn't work in the real world because of the second law.

The second law of thermodynamics

tells us that energy tends to spread out through processes like friction.

Any real machine would have moving parts

or interactions with air or liquid molecules

that would generate tiny amounts of friction and heat,

even in a vacuum.

That heat is energy escaping,

and it would keep leeching out,

reducing the energy available to move the system itself

until the machine inevitably stopped.

So far, these two laws of thermodynamics

have stymied every idea for perpetual motion

and the dreams of perfectly efficient energy generation they imply.

Yet it's hard to conclusively say we'll never discover a perpetual motion machine

because there's still so much we don't understand about the universe.

Perhaps we'll find new exotic forms of matter

that'll force us to revisit the laws of thermodynamics.

Or maybe there's perpetual motion on tiny quantum scales.

What we can be reasonably sure about is that we'll never stop looking.

For now, the one thing that seems truly perpetual is our search.

3

Answer these questions in your own words. Support your answers with evidence from the video.

01What was the main principle behind Bhaskara the Learned's design for a perpetual motion machine?
Sample answerHe thought that if a wheel had curved reservoirs of mercury, the mercury would always flow to the bottom, making one side heavier and keeping the wheel spinning forever due to the imbalance.
02According to the video, how does the first law of thermodynamics explain why a 'useful' perpetual motion machine is impossible?
Sample answerThe first law says you can't create or destroy energy, meaning a machine can't produce more energy than it consumes. So, there wouldn't be any extra energy left over to do things like power a car or charge a phone.
03In what way do various perpetual motion machine designs, such as the over-balanced wheel or the magnet ramps, fundamentally fail to achieve continuous motion?
Sample answerMany designs fail because the same force that's supposed to start the motion also prevents it from continuing. For example, the magnet holds the ball at the top, or the heavy side of a wheel just makes it swing like a pendulum and stop. They'd need to create extra energy to keep going, which breaks the first law.
04Even if a machine didn't violate the first law of thermodynamics, why would the second law still prevent it from being a perpetual motion machine in the real world?
Sample answerThe second law states that energy always spreads out, mainly through friction and heat. Any real machine has moving parts that create friction, which generates heat. This heat is energy escaping the system, so the machine would constantly lose energy and eventually stop, even in a vacuum.
4

Vocabulary

Vocabulary
These expressions will help you communicate more naturally about this topic.
Examples
defy the laws of physics — to go against or seem to break the established scientific rules that govern how the universe works.
Usage note: This phrase is often used to describe something that seems impossible or miraculous. In discussions about perpetual motion, it explains why such machines cannot exist.
harness energy — to control and make use of natural resources, especially to produce power for a specific purpose.
Usage note: This is a common collocation when talking about energy production. You can harness solar energy, wind energy, or even the power of a river.
an elusive dream — a goal or ambition that is very difficult or impossible to achieve, often because it is not realistic or practical.
Usage note: 'Elusive' means hard to find, catch, or achieve. This phrase is used for aspirations that remain just out of reach, like the idea of a perpetual motion machine.
fundamental principle — a basic, essential truth or belief on which a theory, system, or idea is based.
Usage note: This collocation is frequently used in scientific, philosophical, or ethical contexts to refer to core rules or truths, such as the fundamental principles of thermodynamics.
break new ground — to make a new discovery or do something that has not been done before, often leading to significant advancements.
Usage note: This idiom is used to describe innovation and pioneering work in any field, from science and technology to art and medicine. A perpetual motion machine, if it worked, would certainly break new ground.
5

Complete the sentences with words from the box. One word is extra.

Word bank
01Many early inventors tried to create machines that seemed to by producing work indefinitely without fuel.
02The ability to from renewable sources like solar and wind is crucial for our future.
03For centuries, creating a machine that runs forever has remained for many inventors.
04The conservation of energy is a that states energy cannot be created or destroyed.
05Scientists hope to in fusion power, potentially providing limitless clean electricity.
6

Understanding energy concepts

Match each item on the left with the correct item on the right.

A
B
7

Words to take with you

Vocabulary
These expressions are not in the video but will help you discuss this topic more fluently.
Examples
self-sustaining system — a system that can maintain its operation or existence without external energy or resources.
This phrase is used to describe something that keeps itself going. For example, "A truly self-sustaining system for energy production is still a scientific aspiration."
energy conservation — the scientific principle stating that energy cannot be created or destroyed, only transformed from one form to another.
This is a core concept in physics. You can say, "The law of energy conservation is a major reason why perpetual motion machines are considered impossible."
technological breakthrough — a significant and sudden advance in technology or knowledge that solves a problem or opens new possibilities.
Use this phrase to talk about major innovations. "Developing a working perpetual motion machine would be an incredible technological breakthrough."
theoretical concept — an idea or principle that exists only in theory and has not been proven or realized in practice.
This is useful for discussing ideas that are not yet practical or are purely abstract. "Many early perpetual motion designs were interesting as theoretical concepts, but failed in reality."
practical application — the real-world use or purpose of an idea, theory, or invention.
Use this to discuss how an invention or idea can be used in daily life or industry. "Inventors often struggle to find a practical application for their most complex ideas."
8

Use the word in brackets to form a new word that fits each gap.

01
The idea of perpetual motion is often met with because it appears to contradict fundamental scientific principles.
02
The of solar power has revolutionized how many homes generate electricity.
03
For centuries, the dream of perpetual motion has remained for inventors, despite countless attempts.
04
Understanding the principles of thermodynamics is essential to grasp why perpetual motion is considered impossible.
05
A true in energy technology would involve creating a system that requires no external input.
06
Many have dedicated their careers to disproving the feasibility of perpetual motion machines.
9

Useful phrases: Discussing scientific innovation and challenging ideas

Vocabulary
When we talk about new technologies, scientific breakthroughs, or ideas that push the boundaries of what we know, it's useful to have phrases that help us express curiosity, skepticism, and optimism. These phrases will help you engage in discussions about complex scientific topics and the pursuit of ambitious goals.
Examples
It really makes you wonder if we could ever truly defy the laws of physics. — Introduces a speculative or challenging thought related to scientific limits.
Register: Neutral. Use when pondering the feasibility of something that seems to go against established scientific understanding.
While the idea of [X] is fascinating, it often feels like an elusive dream, doesn't it? — Expresses polite skepticism or acknowledges the difficulty of achieving a grand goal. (e.g., 'While the idea of limitless energy is fascinating...')
Register: Neutral. Use when discussing ambitious but potentially unrealistic projects, inviting agreement or further discussion.
From a fundamental principle standpoint, it's hard to see how that could work. — Grounds an argument or doubt in basic, accepted scientific or logical rules.
Register: Neutral/Slightly formal. Use when explaining why something might be impossible or highly improbable based on known facts.
Imagine if we could finally break new ground and harness energy in a completely novel way. — Expresses hope or excitement about future innovation and overcoming current limitations.
Register: Neutral/Enthusiastic. Use when discussing the potential for revolutionary discoveries or technologies.
The biggest hurdle is always figuring out how to overcome the inherent challenges without defying established principles. — Highlights the difficulty in innovation while respecting existing scientific understanding.
Register: Neutral. Use when discussing the practical difficulties of developing new technologies or theories.
Ultimately, the pursuit of such ambitious goals, even if they seem like an elusive dream, often leads to unexpected breakthroughs. — Offers a reflective conclusion on the value of pursuing difficult scientific or technological challenges.
Register: Neutral. Use when summarizing a discussion about challenging scientific endeavors, emphasizing the journey's value.
10

The elusive dream of perpetual motion

Read the passage about perpetual motion machines and fill in the blanks.

Fill in each blank with the correct word from the word bank.

Word bank
The concept of a perpetual motion machine, a device capable of running indefinitely without an external power source, has long fascinated inventors. Such a machine would seem to the laws of physics, particularly the first and second laws of thermodynamics, which state that energy cannot be created or destroyed, and that entropy always increases. Despite countless attempts, building a true perpetual motion machine remains elusive dream. Inventors continue to explore innovative ways to energy more efficiently from existing sources, rather than trying to create it from nothing. While the idea of infinite energy is appealing, understanding and respecting the principles of energy conservation is crucial. Perhaps future breakthroughs will new ground in energy storage or conversion, but the fundamental challenge of creating energy from nothing persists.
11

The enduring pursuit of perpetual motion

The idea of a machine that never stops running has fascinated people for centuries. Read about why this concept remains a challenge.

Read the passage below, then answer the comprehension questions.

The concept of a perpetual motion machine, a device capable of running indefinitely without an external energy source, has captivated inventors for centuries. Imagine a world where we could effortlessly harness energy, free from the constraints of finite resources or environmental impact. This vision, however appealing, consistently runs up against a formidable barrier: the fundamental principles of physics. Specifically, the laws of thermodynamics clearly state that energy cannot be created or destroyed, only transformed, and that some energy is always lost as heat during any conversion.

Despite countless attempts throughout history, no one has ever succeeded in building such a machine. Each design, no matter how ingenious, ultimately fails because it attempts to defy the laws of physics. For many, the perpetual motion machine remains an elusive dream, a tantalizing 'what if' that continues to inspire. Yet, the very pursuit of this impossible goal has sometimes led to unexpected advancements, pushing the boundaries of engineering and forcing scientists to break new ground in understanding energy systems, even if the ultimate prize remains out of reach.

01What is the main characteristic of a perpetual motion machine, according to the passage?
Sample answerIt is a device that can run forever without needing any external energy source.
02Which fundamental principles of physics are mentioned as the reason perpetual motion machines cannot exist?
Sample answerThe laws of thermodynamics, which state that energy cannot be created or destroyed, and that some energy is always lost as heat.
03Why is the idea of a perpetual motion machine referred to as an "elusive dream"?
Sample answerIt's called an elusive dream because it's a highly desired goal that has proven impossible to achieve, despite many attempts throughout history.
04What unexpected benefit has sometimes come from the historical attempts to create perpetual motion machines?
Sample answerThe pursuit of these machines has sometimes led to unexpected advancements in engineering and a deeper understanding of energy systems.
12

The perpetual motion paradox

Explore the scientific and historical pursuit of perpetual motion machines.

Fill in each blank with the correct word from the word bank.

Word bank
The concept of a perpetual motion machine, a device capable of running indefinitely without an external power source, has long captured human imagination. Such a machine would seem to the laws of physics, particularly the first and second laws of thermodynamics, which state that energy cannot be created or destroyed, and that entropy always increases. For centuries, inventors have pursued this idea, hoping to limitless energy. However, despite numerous attempts, a true perpetual motion machine remains an dream. The scientific consensus is that these devices are impossible because they contradict a principle of energy conservation. While the pursuit of such inventions may never new ground in practical terms, it has often spurred innovative thinking about how we might more efficiently utilize existing power sources.