# Newton's First Law

1. Nov 22, 2006

### Eddard

Im wondering what situations involving objects in motion , you could take advantage of Newton's first law of motion?

I have one situtaion but im not sure of another one that could be considered taking advantage of Newton's law...

2. Nov 22, 2006

### PhanthomJay

What does Newton's 1st Law say about objects in motion? What situation did you come up with?

3. Nov 22, 2006

### Eddard

Well off the top of my head Newton's first law of motion is
" An Object in a constant state of motion, will remain in a constant state of motion unless acted upon by an external net force"

I can easily think of example just not one that would be considered taking advantage of it...my example was cutting a log with an axe. You first hit the log lightly so it is stuck on the blade of the axe then you swing it down and when you hit a hard surface (A stump) the wood stops but the axe keeps moving through the log cutting it in half....

4. Nov 22, 2006

### PhanthomJay

5. Nov 23, 2006

### physics.guru

Newton's First law implicitly defines what a force is by describing what happens in the absence of forces.

In the absence of forces and when viewed from an inertial reference frame an object at rest will remain at rest and an object in motion will maintain its motion at a constant velocity (constant speed along a straight line).

Also, the first law implies the concept of inertial reference frames:

If an object does not interact with any other objects, it is possible to identify a reference frame in which the object has zero acceleration (thus a constant velocity which may or may not be zero).

Newton's second law tells us what happens when the net force is zero:

When viewed from an inertial reference frame, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

Examining the first and second laws closely, we see there is a slight difference. Although it is correct to say that in the absence of forces an object has a net force of zero, the converse is not true. It is highly possible for an object to have several forces acting on it and the net force be zero. Case in point: an object at rest on the earth's surface. Gravity and the normal force are acting on the object, but the net force is zero.