Physics, the study of matter, energy, and the fundamental forces of nature, is one of the oldest and most profound sciences. It explains everything from the motion of planets to the behavior of tiny particles. Yet, despite its fundamental role in understanding the universe, physics is often misunderstood, even by educated people. This is not surprising -- physics challenges our intuitions, defies common sense at times, and demands careful reasoning.
Many of these misconceptions arise because our everyday experiences do not always align with physical laws as they are expressed formally. Others persist because of outdated models, oversimplified teaching methods, or miscommunication. Understanding and correcting these misconceptions is essential, not only for students of physics but for anyone trying to make sense of the world.
In this article, we explore some of the most common misconceptions about physics, why they persist, and what the correct understanding should be. The aim is to shed light on areas where intuition misleads us and to help foster a more accurate grasp of this fascinating subject.
1. "An object in motion needs a force to keep it moving."
Perhaps the most widespread misconception stems from everyday experience: you push a ball, and it eventually stops; you have to keep pedaling to keep a bicycle moving. This seems to suggest that things naturally come to rest unless you keep applying force.
However, according to Newton's First Law of Motion, an object in motion stays in motion at constant velocity unless acted on by a net external force. The ball or bicycle slows down not because motion "requires" force, but because of friction and air resistance acting as opposing forces. In the absence of such forces -- say, in space -- an object would keep moving indefinitely.
2. "Heavier objects fall faster than lighter ones."
This belief dates back to Aristotle, who posited that heavier objects fall faster. Galileo disproved this through experiments, showing that in the absence of air resistance, all objects fall at the same rate under gravity.
The misconception persists because, again, our experience is dominated by air resistance. A feather seems to fall slower than a stone, but that's due to drag, not to their weight per se. On the Moon, where there's no atmosphere, a hammer and a feather fall at the same rate.
3. "Weight and mass are the same thing."
These two quantities are often confused. Mass is the amount of matter in an object -- a measure of its inertia -- and is constant regardless of location. Weight is the force exerted on that mass by gravity. An astronaut's mass stays the same whether on Earth or the Moon, but their weight on the Moon is only about 1/6 of what it is on Earth.
4. "Zero gravity means no gravity."
We often hear that astronauts in orbit experience "zero gravity," implying there is no gravitational force. In reality, gravity is still very much present in orbit -- it's what keeps the spacecraft circling Earth. Astronauts appear weightless because they are in free fall, continuously falling around Earth at the same rate as their spacecraft. The proper term is microgravity, not zero gravity.
5. "Centrifugal force pushes objects outward."
People often believe that when a car turns, for example, there's a force pushing them outward. This so-called centrifugal force is not a real force in an inertial frame of reference; it's a fictitious force we perceive due to our inertia. What's actually happening is that your body tends to keep moving in a straight line (Newton's First Law), while the car turns under you.
6. "Electricity flows at the speed of light."
This idea confuses the drift speed of electrons with the speed of the electric field's influence. Electrons in a wire move very slowly -- on the order of millimeters per second -- but the electromagnetic signal propagates at nearly the speed of light.
7. "The seasons are caused by Earth being closer to the Sun in summer."
Many people believe that Earth is hotter in summer because it is closer to the Sun. In reality, the seasons are due to the tilt of Earth's axis relative to its orbit. When the Northern Hemisphere is tilted toward the Sun, it experiences more direct sunlight and longer days -- summer -- while the Southern Hemisphere experiences winter, and vice versa.
8. "Black holes suck everything like a vacuum cleaner."
Black holes are often imagined as cosmic vacuum cleaners indiscriminately sucking up everything around them. In truth, black holes obey the same laws of gravity as any other mass. If the Sun were replaced by a black hole of the same mass, Earth would continue orbiting as before. Only objects that come within the event horizon can no longer escape.
9. "Humans only use 10% of their brain."
While not strictly a physics misconception, this idea is sometimes linked to the brain's "energy potential" or to ideas about energy in general. It's simply false -- neuroimaging shows that we use virtually all parts of our brain at different times. No part of the brain is completely inactive.
10. "Sound can travel through space."
In science fiction movies, we hear the roar of spaceships and explosions in the vacuum of space. In reality, sound requires a medium -- air, water, or solid matter -- to propagate. Space is essentially a vacuum, so sound cannot travel through it.
11. "Heat is the same thing as temperature."
Heat and temperature are related but distinct concepts. Temperature measures the average kinetic energy of particles in a substance, while heat refers to the transfer of energy due to a temperature difference.
12. "Light always travels at the speed of light."
This statement is true only in a vacuum. When light passes through a medium like water, glass, or air, it slows down. This slowing is responsible for effects like refraction.
13. "Air has no weight."
Because we don't feel it directly, many assume that air is weightless. In reality, air has mass and exerts pressure due to gravity. That's why atmospheric pressure at sea level is about 101,325 Pascals.
14. "A plane flies because of equal and opposite upward force from air."
Textbook explanations often simplify lift by saying the shape of a wing creates faster airflow over the top, lowering pressure and creating lift. While this is partially true, it's incomplete and misleading. Wings generate lift through a combination of pressure differences and the deflection of air downward (Newton's Third Law).
15. "Relativity only matters at near-light speeds."
While the effects of Einstein's theory of relativity become dramatic at high velocities, it actually has measurable effects at much lower speeds as well. GPS satellites, for instance, must account for both special and general relativity to maintain accurate positioning.
Why Do Misconceptions Persist?
Misconceptions endure for several reasons:
- Everyday experience: Our intuitions are shaped by friction, air resistance, and limited ranges of velocity and mass.
- Simplified teaching: Teachers often simplify concepts to make them accessible but without clarifying that such models are approximations.
- Language: Common language blurs distinctions between scientific terms (e.g., weight vs. mass, force vs. energy).
- Media: Movies and TV often depict physics inaccurately for dramatic effect.
- Outdated ideas: Historical misconceptions, like Aristotle's, take a long time to die.
How to Overcome Misconceptions
To address these misunderstandings, it helps to:
- Perform experiments: Simple experiments can reveal the reality behind the laws of physics.
- Ask why: Question assumptions and look deeper into the reasoning behind explanations.
- Use precise language: Learn the correct terminology and use it carefully.
- Study counterintuitive examples: Space travel, atomic physics, and relativity challenge our intuitions and expand our understanding.
- Learn the history of physics: Understanding how ideas evolved helps appreciate why certain misconceptions arose and how they were disproven.
The Beauty of Physics
Part of the beauty of physics is that it allows us to see the world in a way that transcends intuition. Correcting misconceptions not only makes us better students of science but also deepens our appreciation of the universe.
Physics may be counterintuitive, but it is also exquisitely logical and endlessly fascinating -- once we shed the myths and embrace the truth.
You can learn these concepts and more at Dr Hock's maths and physics tuition.