Physics is the oldest branch of science. There were a lot of misconceptions about physics since its inception. Even accepted theories became wrong after centuries. But did you know some things you learned in childhood are misconceptions in physics? So why did they teach those? Let’s take a look at 10 common misconceptions about physics.

## Heavier objects fall faster than lighter ones

If I drop a rock and a feather at the same altitude, the rock will hit the ground first, right? So, why is it wrong?

This misconception has a long history. Aristotle believed this was true because he believed heavier objects witness a larger force than lighter objects. He did not stop there he claimed twice heavier objects fall twice faster. His writing has remained unquestioned for thousand of years.

Galileo Galilei was about 26 years old and a math teacher at the University of Pisa when he took an interest in rates of fall. He experimented on the Leaning Tower of Pisa. He dropped balls with different masses from the top of the tower. Surprisingly, they hit the ground at close times. Galileo said in his report air resistance causes a little difference.

The Apollo 15 Hammer-Feather Drop is a great example. David Scott was the seventh human being to set foot on the Moon. He did something interesting. He drops a feather and a geological hammer from the same altitude at the same time on the moon. If we did it on earth, the feather will take some time to hit the ground than the hammer take. But on the moon does not have a dense atmosphere. So, they both landed at the same time.

It was the experimental debunk of this myth. David said “Galileo was correct” after the live demonstration.

## An object becomes hard to push when it is heavy

This is another common mistake amount students and common people. You may have experienced that heavy objects are hard to move. Sure, the mass of an object has a significant effect on this. But it is not the only affecting factor and weight is not the force against your push.

First, we need to know why a force is required to move an object. Friction is a type of force. It acts against moving of an object. Rough surfaces between two objects are the reason for friction. It is given by the below equation,

F =µN

Here, F is the friction force, µ is the coefficient of friction and N is the normal force. If additional forces are not applied, N is equal to the weight of the object. The coefficient of friction depends on the physical nature (usually roughness) of the materials and temperature.

If you try to push two objects of the same weight, one has a smooth surface and the other has a rough surface, the rough one will be harder than the smooth one. The wheel is an application of friction.

## The acceleration is 0 at the top of a projection

If you thought this was true, you are mistaken. When you throw an object on earth, earth’s gravity pulls that object to the ground. Remember Newton’s second law of motion. An object is not changing its state of motion until an external unbalanced force act on it. Also, the acceleration of the object will be in the direction of the unbalanced force and the force is proportional to mass and the acceleration of the object.

Weight is acting on every object on earth. When it is in the air, weight is an unbalanced force acting on it. So, according to Newton’s second law of motion acceleration of an object can not be 0 until the projected object lands.

So what makes this common misconception about physics. We know the velocity of the object becomes 0 at the top of the projection. Many people confused themselves with velocity and acceleration. If air friction wasn’t a thing, the acceleration of an object is always equal to gravitational acceleration (Close to 9.8ms^{-1} in most areas).

## Velocity simply adds together

If a trolley is moving with 2ms^{-1} velocity and a man on that trolley runs with 2ms^{-1} velocity in the direction of the trolley’s movement what is the velocity of the man relative to the earth frame? Is it 4ms^{-1}?

In high school physics, we added two velocities together simply like that. But have you known it is wrong? What we did was what we do for any vector. It is correct according to Newtonian physics. But completely wrong in general relativity.

The correct answer is very close to four but not for. We use V = V_{1} + V_{2} equation for our calculation. But the correct equation we should have used is below,

Change is very small because the velocity of light (c) is large. Unfortunately, it is enough for adding to our 10 common misconceptions about physics list.

## A continuous force is needed for continuous motion

A car, roller or any other objects on earth need a force for continuous motion. Everyone has experienced it. What will happen if you stop paddling a bicycle. It will deaccelerate and eventually stop and fall with you. So, how this is one of 10 common misconceptions about physics.

According to Newton’s 2^{nd} law of motion, an object does not change its state of motion until an external unbalanced force is act on it. So, if it is true when we add a force to an object and accelerate it then stop the force, the object should move in constant velocity. But why it does not happen practically.

On earth, other forces can act on a moving object. Friction, air friction, and viscosity are some phenomena that create forces to stop a moving object. But if you do that in deep space, the object will travel until the gravity of another object affects its path.

Even though practically this claim has some credibility it is theoretically invalid.

## Planets move in circular orbits around the Sun

People first thought the sun, planets, and stars orbit around earth. It is called the geocentric model. Nicolaus Copernicus was the first to introduce the theory of the Universe which earth and other planets rotate around the sun. At first, this does not gain the approval of authorities.

Later Johannes Kepler introduced his three laws of planetary motion. The first law was “Each planet’s orbit about the Sun is an ellipse”. His laws could accurately describe the motion of planets and commits.

Why do planets move in elliptical orbits around the sun? No one could answer this question until Isaac Newton invented calculus. A circular orbit is ideal. But gravitational forces between planets are not consistent. These gravitational interactions force planets to move in elliptic orbits.

But if you consider the eccentricity of orbits, most planets are close to circles rather than an extreme ellipse. Mercury has the most elliptic orbit in the solar system with 0.206 an eccentricity. Venus has the most circular one (0.007 orbital eccentricity) in our solar system. Our earth’s orbital eccentricity is 0.017

Planets sometimes get closed to the sun and sometimes get away from the sun because of the elliptic motion. The acceleration is maximum when it is closest to the sun.

## If the acceleration of an object is negative it should be slowing down

This is a common myth among students. Acceleration is known as the rate of change in the velocity. More precisely, acceleration is the derivative of velocity with respect to time. It is a vector.

We study every motion respective to a frame of reference. All calculations are made with a coordination system. If an object moves in the positive direction of our coordinate system and its velocity is reduced 4ms^{-1} to 2ms^{-2} in 1 second, we say it is a -2ms^{-2} acceleration. In this case, the object slows down. But how about this acceleration last long for another minute.

The object will stop (0ms^{-1} velocity) and in intense it will start to move in the opposite direction. Still, the object has -2ms^{-2} acceleration but it is not slowing down. It is speeding up in opposite direction. So, just because the acceleration of an object is negative or positive, we can not say it is slowing down or speeding up.

## Electrons orbit the nucleus like planets orbit (move around) the Sun (in solar system)

The planetary model of atomic was first introduced by Joseph Larmor in 1897. It took a special place in Neil Bohr’s and Rutherford’s atomic models. In the planetary model, electrons orbit around the nucleus (Protons and neutrons) like in the solar system planets orbit around the sun.

The plum pudding model, planetary model, Bohr model, and the electron cloud model are four atomic models. Lastly mentioned electron cloud model is the most widely accepted model now. Protons and neutrons are in the nucleus like in the planetary model and Bohr model. But the motion of electrons is different.

Instead of orbits, electrons’ motion is not predefined here. The electron cloud model defines regions where there is a greater than 90% probability of finding the electron at any given moment. The geometry of these areas of probability varies with the energy level of the electrons.

So electron does not orbit around the nucleus. It is a misconception.

## Gravity is a force of attraction. It occur between two objects with a mass

This is what Newton told us. It was a widely accepted explanation until the greatest scientist of the 20^{th} century Albert Einstein introduced the general theory of relativity.

Are we living in a three-dimensional world? We can move in three dimensions. But we exist in a 4^{th} dimension realm called spacetime. The existence of spacetime is what causes gravity.

Imagine a trampoline. Now think we added two balls with different weights. The trampoline is curved by the objects. A lighter ball will collide with the heavy ball because of the curvature. Stars, planets, or any object is doing a similar thing with spacetime.

## There is no gravity in outer space

Many people have seen astronomers floating in space. So they believe this common misconception about physics. Gravitational force depends on two factors. Mass of the bodies and distance between them. Astronauts don’t feel gravity like earth because away from earth and there is no heavy object near them. But gravity exists between every object in the universe.

That is our 10 common misconceptions about physics. Feel free to let us know what you think about the blog. Check out other interesting physics topics.