Consider the following actions: 1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously 2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive 3. Detection of the tilt of the smart-phone which results in the rotation of display between portrait and landscape mode In how many of the above actions is the function of accelerometer required?

Let's examine each action to determine if an accelerometer is required:

1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously. This statement is correct. Accelerometers are essential sensors in car safety systems. They detect sudden and significant deceleration (change in velocity over time), indicating an impact or crash, which then triggers the deployment of airbags.

2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive. This statement is correct. Many laptops are equipped with accelerometers (often part of a 'free fall sensor'). When a free fall is detected (a rapid acceleration towards the Earth's gravitational pull), the accelerometer signals the system to 'park' the hard drive heads, preventing damage to the platters upon impact.

3. Detection of the tilt of the smart-phone which results in the rotation of display between portrait and landscape mode. This statement is correct. Accelerometers measure acceleration, including the acceleration due to gravity. By sensing changes in the orientation relative to gravity, the accelerometer determines the tilt of the smartphone, allowing the operating system to rotate the display accordingly.

All three actions fundamentally rely on the ability of an accelerometer to detect changes in motion, acceleration, or orientation.