The main physical property used in a flashlight is electricity. Here's how it works:

* Electrical energy is stored in the batteries.

* When you turn the flashlight on, you complete a circuit, allowing the electrical energy to flow.

* This flow of electricity passes through a bulb (usually LED).

* The electrical energy is converted into light energy in the bulb, making the flashlight shine.

So while the flashlight itself is a physical object, the primary property that makes it work is the flow of electricity.