# About Newts First Law of motion

• PiRsq
In summary, the first law states that an object has a netforce of zero when its at rest or moving at a constant velocity.

#### PiRsq

About Newts First Law of motion...

U kno the first law of motion..."Object has a netforce of zero when its at rest or moving at constant velocity..." I don't get how you could say an object has a total netforce of zero when its moving...If its moving in one direction then isn't a force acting on it to go in that direction?

Um ... not exactly.
This is something that find hard to understand at first, but eventually it is understandable.

First you have to understand that this is a law of nature, so we cannot really say 'why', we only put laws to understand nature.

What may seem illogical for you now is that you need a force in order to make an object moving in a constant velocity.
Well, you do not need the force to maintain its speed, as long as the net (or resultant) force is zero.

In our everyday life experience, there is always friction and air drag acting on moving objects, therefore we always need a force to make an object move at a constant velocity.
What this force that we provide actually does is that it works against the resistance forces (friction and air drag and maybe other forces) to make the net force zero, which will make the object move at a constant velocity.

Tell us if you still feel there is something you don't understand.

I hope i helped.

I think I understand a little better, its just hard to imagine a object in a vacuum I guess...

Consider that a tiny moving object has two properties because of its motion. It has a speed and a direction. Now Newton saw that neither one of these properties could just change without some cause acting. The kind of causes that act to change the speed or direction (or both) of a moving object are called Forces.

An ordinary object moving through the air will feel two kinds of forces: the air pressure which tends to decrease its speed in the direction of motion, and gravity which continually adds a certain speed change in the down direction.

Originally posted by PiRsq
U kno the first law of motion..."Object has a netforce of zero when its at rest or moving at constant velocity..." I don't get how you could say an object has a total netforce of zero when its moving...If its moving in one direction then isn't a force acting on it to go in that direction?

Dock, Please restrict your misinformation to the Theory Development fourm Integral

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Originally posted by PiRsq
If its moving in one direction then isn't a force acting on it to go in that direction?

Hi PiRsq,
well the fact that you ask this question means IMO that you really look at physics from its very birth-place. Yes, for thousands of years it was generally accepted that a force is needed to keep a body in motion. Everyday experience says so, and even the scholars (e.g. Aristotle) wrote this down in their doctrines. But astronomers, since long, have known that there is 'eternal' motion in the sky, as exhibited by the Sun, Moon, and planets circling about. IIRC, even Copernicus and Kepler (who laid the foundations of Physics) assumed that the planets are 'brushed' around the sun by quasi-mechanical devices impeding some tangential force on them (=pushing them). It was Newton who postulated that there is no such pushing force, just gravitational attraction. He postulated that the only force acting on a planet (if you neglect other planets) is directed towards the Sun but not in the direction of the planet's motion (well, for a circular orbit...). This means the planets go on forever without anything actually pushing them. That is maybe the sort of 'motion in vacuum' which you (among many people) find so hard to imagine. Hope this helps a bit

Example: say you're flying in a plane. You toss a ball up in the air. It acts normally -- goes up and comes straight down. If it needed a force to keep it moving, it ought to stop moving forward with the plane as soon as it left your hand, and get slammed backwards. Obviously this doesn't happen. :)

This is a post made by FZ+ which I erronously deleted in an effort ot clean out the post he is reffering to. Sorry FZ!
Integral

It is important to know that force is defined in physics as being the rate of change of momentum, which is m*v. So, if the force is zero, then all it means is that m*v is constant. Further, reality is based not on absolute motion, but on relative motion. So, it is irrelevant without a reference point whether you are at rest or moving at steady velocity. We usually imply relative to the Earth when we say this.

## 1. What is Newt's First Law of Motion?

Newt's First Law of Motion, also known as the Law of Inertia, states that an object at rest will remain at rest and an object in motion will remain in motion at a constant velocity unless acted upon by an external force.

## 2. Who is Newt and why is this law named after him?

Sir Isaac Newton, commonly known as Newt, was an English physicist and mathematician who developed the three laws of motion. This law is named after him because he was the first to formally describe it in his famous work "Principia Mathematica".

## 3. How is Newt's First Law of Motion different from the other two laws?

Newt's First Law of Motion deals with the concept of inertia, while the second and third laws deal with acceleration and action-reaction forces, respectively. The first law is also sometimes referred to as the "law of inertia" while the other two are known as the "law of acceleration" and "law of action-reaction".

## 4. Can Newt's First Law of Motion be applied to everyday life?

Yes, this law can be observed in many everyday situations. For example, when a car suddenly stops, passengers inside may feel like they are being pushed forward. This is due to the law of inertia - the passengers were moving at the same speed as the car and when it stopped, their bodies continued to move forward until an external force (such as the seatbelt) stopped them.

## 5. What is the practical significance of Newt's First Law of Motion?

The practical significance of this law is that it helps us understand and predict the behavior of objects in motion. It also serves as the basis for understanding the other two laws of motion and is essential in fields such as engineering, physics, and astronomy.