Why do Newton's laws only apply in inertial reference frames?

[member 392791]

Hello, I am having difficulty understanding the concept of Newton's first law only applying in an inertial reference frame, or a frame that is at constant velocity, however, apparently the 1st law no longer applies if the reference frame is accelerating. Can anyone give me some sort of concrete example so I can see it in my mind, right now it's not making any sense to me. Actually, I just need an explanation of the whole concept of inertial vs noninertial reference frame.

 

[jedishrfu]

If you're floating out in space that's an inertial frame. If you toss a ball it will go straight at a constant velocity.

In contrast a non-inertial frame is where you're standing on the Earth and you toss a ball the ball travels in a curve.

A pool table simulates an inertial frame in the xy plane ie z is height above the ground. Setting a ball in motion it will move straight and only slow due to friction.