Turn an led with a jerk or impact using accelerometer

how can i make a flashlight which turns by the action of chopping (twice) as in most of the moto devices ?

Easy. Use something like an accellerometer or impact sensor, and when you read two "chops" on your sensor you switch on the light. That's pretty much all there is to it. Well, almost: you may want to think of a way to switch it off again.

I am unfamiliar with this 'chopping' flashlight. Can someone ELI5?

If you're going to make a proper flashlight, you better include a wrist strap if you're expecting people to daftly wave it around to turn it on.

INTP: I am unfamiliar with this 'chopping' flashlight. Can someone ELI5?

Swing your phone up and down twice, like you would when chopping something with a knife or an axe, and the flashlight turns on (do it again and it turns off). Wiggling it left/right turns on the camera. I suppose the phone is doing it with the built-in motion detectors.