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Newton’s Three laws of motion (Part 1)

Hi guys,

I’m terribly sorry for being inactive for such a long time. I have been extremely busy lately therefore not having time to update the blog. So to make up for it i’m going to explain Newton’s three laws of motion. I will be posting these in 3 separate posts, explaining 1 law per post and this is part 1. I feel that this fundamental concept is extremely important in understanding other concepts as it is extremely simple, easy to understand and at the same time very significant.

Okay so on to the three laws of motion.

So what are the three laws of motion? They are Laws of physics which can predict the motion of an object pretty accurately (Although not as accurately as Quantum Physics which was developed by Einstein around 300 years after Newton formulated these laws.)

The three laws of motion are as follows:

  1. When viewed in an inertial reference frame, an object either is at rest or moves at a constant velocity, unless acted upon by an external force.
  2. The acceleration of a body is directly proportional to, and in the same direction as, the net force acting on the body, and inversely proportional to its mass. Thus, F = ma, where F is the net force acting on the object, m is the mass of the object and a is the acceleration of the object.
  3. When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body.

Okay that might have been a little too complicated. but on to the explanations.


Let’s analyze Newton’s first Law of Motion

“When viewed in an inertial reference frame, an object either is at rest or moves at a constant velocity, unless acted upon by an external force.”

So what does this mean?

Newton’s first law of motion is also known as the law of inertia and inertia is the tendency of an object to remain in its state of motion be it not moving at all or moving at 10000000 km/h. Heavier bodies possess more inertia while lighter objects possess less inertia so heavier objects are more difficult (requires more force) to speed up but more difficult to stop and lighter objects though easier to speed up, are easier to stop.

Imagine a bus and a feather in front of you. Which is easier to move? The feather. Imagine the bus is now moving at 40 km/h and the feather is also moving at 40 km/h. Which one is easier to stop now? The feather.

So what does any of that have to do with anything?

Well simply put Newton’s first law of motion states that an object will stay stationary or continue moving in a constant velocity in a straight line if no forces (resultant) are acting upon it. This idea is expressed in terms of mass with inertia.

So why do things eventually stop?

Well that is because there are other forces acting upon the object.

Friction, Gravity, Normal Forces and practically any type of force can oppose other forces, cancelling them out and thus causing the object to stop.

Try pushing both you hands against each other and use as much force as possible to push your hands against each other. Despite applying so much force, your hand remains fairly stable and in roughly the same place. Why does this happen? The forces cancel each other out, therefore your hand remains stationary.

As you may have noticed, I have been using the word “resultant” very often. Why is this so?

Resultant force is the final value of the force acting upon an object after taking into account all other forces. Lets say we have a book that is falling. In this case there are 2 forces acting on the object: Gravity and Air resistance. Assuming the gravity acting upon this book is 10N and the air resistance acting on the book is 5N the resultant force will be 5N downward with gravity.

This resultant force value can be calculated with a simple formula which I will explain in my second post.

And with that I end this post. Thanks for your continuous support of my blog and I wish you a good day!


Best Wishes,

Clyde Lhui 🙂


P.s: Once again im very sorry for being so inactive. I had to spend quite some time catching up with school work but I promise that I will work on this whenever I can!