High School Inertial vs non inertial frames

[rudransh verma]

I previously thought Earth is inertial frame and relative to Earth non accelerating frames are inertial too. But after watching this video, I came to know that it’s not the frame with respect to which we decide whether a frame is inertial or not. It’s the particle.
When a particle is not accelerating the frame is inertial. When it’s accelerating frame is non inertial.
But how the author is saying there is acceleration even when the net force is zero? I don’t get that part.
Also for example we take Earth and lift example. If our lift is accelerating then what does that make the earth, a non inertial frame or inertial ?

 

[weirdoguy]

I previously thought Earth is inertial frame

It can't be since it is rotating. Rotating reference frames are not inertial. But sometimes we can neglect those effect, and treat frame connected with Earth as inertial, but that is an approximation.

 

[vanhees71]

Another very illuminating movie, one of my favorites, is

 

[Steve4Physics]

Also for example we take Earth and lift example. If our lift is accelerating then what does that make the earth, a non inertial frame or inertial ?

Part of the skill of physics/engineering is to know how to think about a problem.

Suppose you are doing experiments in a lab’ with colliding objects on an air-track. The fact that the Earth is rotating (so is non-inertial) is irrelevant – the effects on the experimental results are too small to have any detectable effects. You are therefore justified in treating the Earth as an inertial frame.

But if you are a meteorologist analysing large-scale patterns of air flow in the atmosphere., you cannot ignore the earth’s rotation. You must treat the Earth as a non-inertial frame. (Read about Coriolis force if you are not already familiar with it.)