Showing posts with label Fundamentals. Show all posts
Showing posts with label Fundamentals. Show all posts

10 Examples of Physics From Everyday Life

law of inertia of motion

Not every student will grow up and study physics on a deeper level, but physics extends well into our daily life, describing the motion, forces and energy of ordinary experience. Therefore, it should be possible to illustrate to anyone the physics of everyday life, with examples of course.

Image formation

Have you noticed that when standing inside a room at night, you can often see your reflection in a pane of glass? In similar way, because there is much less light coming from the bottom of a lake, the surface of the lake will act like a mirror.

reflection of light

But an image can also be formed by refraction. A fish seen in the water will usually appear to be at a different depth than it actually is, due to the refraction of light rays as they travel from the water into the air.

refraction of light virtual image

Lastly, there exist phenomena which appear due to combination of reflection and refraction. For example, a rainbow is seen when light passes through water droplets hanging in the atmosphere. The light bends, or refracts, as it enters the droplet, and then reflects off the inside of the raindrop.

how rainbow forms after rain

Washing machine

The dryer of washing machine is a rapidly rotating container that applies centrifugal force to its contents. The centrifugal force acts in a direction away from the centre and hence can be used to throw the water molecules on the clothes radially outwards during the spin cycle of the washing machine.

Static electricity

When two objects that are not good electrical conductors are rubbed together, electrons from one of the objects rub off onto the other.

static electricity funny images animated

The more rubbing between two objects, the more static electricity build up and the larger the electrical charge.

Road safety

When brakes are applied to a moving car, the car and lower portions of the passengers attached to the car come to immediate stop, but their upper portions fall forwards, because of inertia. This is why seat belts as well as air bags are installed in the car.

inertia safety belts in car

Roller coaster

The first hill of the ride is always the highest one so that the car collects enough energy to go through all the elevations. As the car goes down, its potential energy decreases but kinetic energy increases. If added together at any part of the ride, the kinetic and potential energies of the car will equal the potential energy that the car had on the first hill.


When the figure skater draws her arms and a leg inward, she reduces her moment of inertia thus rotating at a faster angular speed. This is due to conservation of angular momentum.

angular momentum figure skating

Handle of the door

If you apply force close to the hinge of the door, the door will not open as it will not be able to rotate about the hinge. But, when you apply the same force farther away from the hinge, the torque will be larger. Hence, the door opens easily with less effort.

Falling down

Suppose you are climbing a tree, and suddenly you slip and fall down from the tree. Then, you may break a bone or two. But if same thing happens to a little ant, that is, if it falls down from height, it does not get hurt. Why is it so?

From ant’s point of view, the atmosphere is thick and viscous and its experience of falling from a height is similar to ours when we fall through water to the bottom of the pool. The air underneath the falling ant becomes like a large cushion of safety.


Nobel prize winning physicist Richard Feynman explains why little drops of water are round in the following video.

Sound game

When a water bottle fills up, the air column or amount of air inside the bottle decreases. As a result, the pitch (or shrillness) of the sound will increase, as it is inversely proportional to the length of vibrating air column. Therefore, you can tell exactly when the bottle is full without even looking.

Summing up

It is hard to imagine of life without physics. Even though one may not be equipped with the kind of mathematics required to fully understand these physical phenomena, one can surely appreciate the fact that they are there. Lots of other examples are available and you just need the eye to recognize them.

Characteristics of Physical Law

Despite numerous limitations, we human beings are able enough to study as well as appreciate the grandeur of the universe. Our great journey of determining scientific laws began as we understood the regular repetitions of the day and night, the annual cycle of seasons, the eclipses, the tides, the volcanoes, the rainbow and so on.

What is scientific law?

A scientific law is verbal or mathematical explanation that describes some phenomenon of the natural world. For example, Newton's law of gravity, which states that every particle attracts every other particle in the universe with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. But the law itself does not explain why the phenomenon exists or what causes it: that is really the job of theory, in this case, Einstein's theory of general relativity.

The scientific law is factual and should not be confused with logical truth. For example, "boiling point of water is 100 degrees celsius" is a law whereas "every number has a double" is logical truth and not really a law.

Constant over space and time

The same laws which apply here on earth also apply to the rest of the universe. For example, Galileo's law of falling bodies was tested on the moon by astronaut David Scott in 1971.

This is simple and yet beautiful truth, that the laws of nature are universally valid. There are no laws of nature that hold just for the planet earth or the Andromeda Galaxy, for that matter.

In addition, the laws of nature do not change as time progresses. There is a joke which goes something like this, "Before Newton discovered gravity, all things could fly." That is so not the case; there are no laws of nature that hold just for the eighteenth century or just for the Mesozoic Era.

Same for animate and inanimate

The laws are same for living beings and for inanimate objects. There is no evidence yet that what goes on in living creatures is necessarily different, so far as the physical laws are concerned, from what goes on in non-living things.

For example, conservation of angular momentum is a fundamental law of nature. A rotating ballerina spins faster when drawing her arms in.

how are physical laws symmetrical?

Similarly, the earth and other planets revolving around the sun obey the law of conservation of angular momentum, which is why, when a planet is nearer to the Sun, the orbital speed increases and when it is farther away, it slows down.

Simple in nature

Eminent kiwi physicist Ernest Rutherford used to say, "it should be possible to explain the laws of physics to a barmaid." But even though the laws themselves are so simple, their implications are far and wide.

For example, Newton's third law of motion is simply, "for every action there is equal and opposite reaction", and yet it is noticeable in many instances of life such as in walking, swimming, recoiling of gun, and most importantly, rocket propulsion.

how are physical laws symmetrical?

Similarly, Newton's second law of motion is just, F=ma, but it made possible the industrial revolution. Steam engines, locomotives, factories, machines, all of it due to the mechanics set into motion by the second law of motion.

Same in uniform motion

If we have an experiment working in a certain way and then take the same apparatus, put it in a car, and move the whole car, plus all the relevant surroundings, at a uniform velocity in a straight line, then so far as the phenomena inside the car are concerned, there is no difference.

Unification of laws

Scottish physicist James Clerk Maxwell took a set of known experimental laws such as Faraday's Law, Ampere's Law and unified them into a symmetric coherent set of equations known as Maxwell's equations.

how are physical laws symmetrical?

Maxwell's equations are also laws just like the law of gravity. They govern the behavior of electric and magnetic fields. Also, light itself is an electromagnetic wave. Therefore, Maxwell's equations have in a way unified three separate phenomena, electricity, magnetism and optics, into one.

A similar type of unification occurred in the early part of the 20th century. The laws of conservation of energy and conservation of total mass were proven to be equivalent by German physicist Albert Einstein in a simple equation, E=mc^2.

These unifications are possible because the laws of physics are symmetrical in nature. Two or more distinctly appearing natural phenomena appear to be governed by just one simple law. Thus, one day, we may be able to find an ultimate law of physics that may explain everything.

Renowned American physicist Richard Feynman had famously said, "God is always invented to explain those things that you do not understand."

Throughout history, man has credited god for this or that phenomena. For example, early Greeks believed that lightning was a weapon of Zeus. Now, when you finally discover how something works, you get some laws which you're taking away from god; you don't need god anymore.

Thus, "what one man calls god, another calls the laws of physics," or in other words, to have an understanding of the physical laws is in a way a liberation from all superstition.

Is gravity a theory or a law?

Is gravity a theory or a law?

Why is it called Newton's law of gravity and not Newton's theory? Is Einstein's theory of general relativity scientifically inferior to Newton's law? Since in our day-to-day usage, the law carries more weight than the word theory?

Questions like these are doing the rounds on the internet. So we see it fit to explain, once and for all, what scientific terminology is. Before studying science, you must know the meanings of such terms like: axiom, hypothesis, experiment, model, law and theory.

Luckily, this terminology is well incorporated in the method of science. So, let us first understand the scientific method with an example and then we will answer whether gravity is a theory or a law. You will be surprised.

It is observed that bees are attracted to flowers. This statement is taken to be true to serve as a premise or starting point for further reasoning and arguments. This is called an axiom.


Then, a natural question arises. Why are bees attracted to flowers? This is the first step of the scientific method. An observation is followed up by a question. Like, on one summer day, Isaac Newton had questioned the fall of an apple.

One may guess that bees are attracted by the color of flowers. Another person may say that bees are attracted by the nectar inside flowers.

All guesses are called hypotheses.

A scientific hypothesis can be tested in laboratory with the help of an experiment. First, bees are let inside a glass chamber containing artificial flowers. Second, bees are let inside another glass chamber containing real flowers. Further observations are noted down.

example of scientific method

It is observed that bees are attracted to artificial flowers, they sit on them briefly, then fly away. Thus, the first hypothesis stands true as bees are indeed attracted by the color. In the second set-up, bees sit on real flowers and remain there for long. So, the second hypothesis is also true.

After hypotheses have been tested, it is time to formulate laws, theories or conclusions on basis of the result. In our case, we come to the simple conclusion: "bees are attracted to flowers due to both color and nectar."

A law, on the other hand, is a formula. Like, Newton's law of universal gravitation is used to calculate the "magnitude" of the gravitational force between two objects of mass separated by a given distance.

Is gravity a theory or a law?
Newton's law

Newton's law is also used in a model so as to mimic remote physical phenomena locally, say on one's computer, such as sky-diving or revolution of Moon around Earth. Thus, a model is generally a simulation. But Newton's law does not attempt to explain how or why gravity works.

In science, theory holds a special place. It is a well-substantiated explanation of the natural world that can incorporate all facts, laws, inferences, and tested hypotheses. So, Einstein's theory of general relativity explains "why" things fall.

While laws rarely change, theories get modified whenever new evidence is discovered. Einstein published his version of the theory in 1915 and since then the theory has adapted as new technologies and new evidence have expanded our view of the universe.

Is gravity a theory or a law?
Is gravity a theory or a law?

So, is gravity a theory or a law? Well, first of all, it is an always acting force that one can feel. Second, it is both a theory and a law. The law of gravity calculates the amount of attraction while the theory describes why objects attract each other in the first place.

You have now an understanding of terms such as axiom, hypothesis, experiment, law, model and theory, by our use of the scientific method. Whenever you encounter a phrase like "it is just a theory" from the other party, you will know where they lack in their understanding.
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