Newton’s First Law of Motion Explained

Newton’s first law

If an object is at rest , it will remain in that state unless applied by an unbalanced force. Similarly if an object is moving , it will remain in uniform motion unless applied by an unbalanced force.

Galileo introduced this theory in late 1500s. He said that objects have a natural tendency to return to their original positions if they are not being applied by a force. If a cycle is to be moved continuously, the person need to apply a force to the paddle. Descartes also said the same thing.

Newton however, disagreed with them. According to Newton;

“An object at rest remains at rest unless applied by an unbalanced force. An object in motion continues to move with the same speed and in the same direction unless acted upon by an unbalanced force”.

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Hence, according to Newton an object maintains its state of motion until an unbalanced force is applied to it. It turned out that Newton was right. For instance a cycle keeps on moving unless its brakes are not applied. The brakes apply a force of friction to the tyre that cause it to stop.

Similarly gravitational force and the air resistance also acting on the tyre cause it to stop if one does not keep paddling. If these forces are made zero. then the cycle will keep on moving. there will be no need to paddle it then. In the same manner a book only rests on a table because the net force acting on it is zero.

Law of Inertia

Newton’s first law is also known as “the law of inertia”.

Inertia is the property of a body to resist change in its motion. 

Lets say you are traveling in a car. Although with respect to the car you are at rest, but you are considered to be moving with respect to the environment. When the brakes are applied, the car may stop but you will tend to be pushed forward due to inertia since your moving body would resist the change in its motion.

Learn how Atmospheric Pressure helps you in Drinking juice


Pressure is a scalar, physical quantity which is the ratio of force to the area over which that force is applied.The formula of pressure is as follows:

P = F/A   

Atmospheric Pressure:

Earth is covered by air containing different gases which makes the atmospheric pressure of earth. The pressure of molecules acts on all bodies from all direction. Take a balloon for instance. If you were to blow air in a round balloon, it would swell in a perfect round shape as the air would put pressure on its insides from all directions. Hence, the balloon would take a perfect round shape.

Real Life Application of Atmospheric Pressure:

Atmospheric Pressure plays an important role in our daily lives as well. We drink juice from a box with the help of Atmospheric Pressure. The act of sucking through a straw creates a vacuum in the box as the air is sucked from it.

When you suck the air out of the straw, the drink in the box is pushed up by the air that is still on top of the drink. You use your mouth to reduce the pressure over the fluid inside the straw. The pressure over the rest of the liquid in the box continues to be exerted and, because it is higher than the pressure over the liquid inside the straw, the net effect is for the liquid to be forced from the area of higher pressure to the area of lower pressure.Hence, the drink goes in your mouth from the straw.

If you keep sucking even when the juice is finished, the box will get pressed inside. This happens because the action of sucking the air creates an area of lower atmospheric pressure in the box. Hence, the air outside which has a higher pressure applies the force on the box, thereby pressing it. Previously, the air inside the box had been exerting an equal pressure on it than the air outside the box. So the box had maintained its shape.

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O Level Physics Videos Available

O Level Physics ADWe have a good news for all the O Level students anxiously waiting for our videos. The wait is over now. The videos covering the complete Cambridge O Level Physics syllabus have been uploaded on our website

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We have followed the exact sequence of Cambridge O Level Physics book. The videos are named and arranged exactly like the index page of Cambridge O Level Physics book. The sequence of all 25 chapters from O Level Physics  has been followed in our videos as following:

Chapter 1: Measurement of Physical Quantities

Chapter 2: Speed, Velocity and Acceleration

Chapter 3: Forces

Chapter 4: Mass, Weight and Density

Chapter 5: Turning Effect of Forces

Chapter 6: Work, Energy and Power

Chapter 7: Pressure

Chapter 8: Measurement of Temperature

Chapter 9: Simple Kinetic Theory of Matter

Chapter 10: Heat Capacity

Chapter 11: Melting and Boiling

Chapter 12: Transfer of Thermal Energy

Chapter 13: General Wave Properties

Chapter 14: Reflection and Refraction of Light

Chapter 15: Converging Lens

Chapter 16: Sound

Chapter 17: Static Electricity

Chapter 18: Current Electricity

Chapter 19: D.C. Circuits

Chapter 20: Practical Electric Circuits

Chapter 21: Simple Phenomena of Magnetism

Chapter 22: Force on Conductor in a Magnetic Force

Chapter 23: Electromagnetic Effects

Chapter 24: Introductory Electronics

Chapter 25: Radioactivity and the Nuclear Atom

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