UPSC Prelims 2023 Q54: Science & Technology – Defence Technology

UPSC Prelims 2023, General Studies Paper I · Science & Technology

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?

(a) Only one
(b) Only two
(c) All three
(d) None

Answer: (c) All three

Explanation

Accelerometer — Applications

An accelerometer measures acceleration forces — both dynamic (movement) and static (gravity). It detects changes in velocity, tilt, vibration, and orientation.

Action	Accelerometer Required?	How
1. Car crash → airbag deployment	YES	The sudden deceleration (large negative acceleration) is detected by the accelerometer, triggering airbag inflation in milliseconds.
2. Laptop free fall → hard drive parks	YES	The accelerometer detects near-zero gravity (free fall condition = acceleration ≈ 0) and immediately parks the hard drive read/write head to prevent damage on impact.
3. Smartphone tilt → screen rotation	YES	The accelerometer detects the angle of gravitational force relative to the device axes, determining portrait vs landscape orientation and rotating the display accordingly.

All three actions require an accelerometer.

Answer: (c) All three.

Why each option is right or wrong

(a) Incorrect. 'Only one' — all three described actions are standard real-world accelerometer applications.
(b) Incorrect. 'Only two' — laptop hard drive parking during free fall is a well-documented accelerometer application (IBM/Lenovo Active Protection System).
(c) CORRECT. All three actions — airbag deployment, laptop hard drive parking, and smartphone screen rotation — require accelerometers to detect acceleration, deceleration, or tilt.
(d) Incorrect. 'None' — accelerometers are fundamental to all three described safety and usability functions.

Key point

Accelerometer detects: crash deceleration (airbag) + free fall (laptop HDD park) + tilt/gravity (screen rotation). All three = accelerometer applications. It measures acceleration forces in all directions.

Remember

An accelerometer is required in all three actions: detecting car crashes for airbag deployment, detecting laptop free fall to park the hard drive, and detecting smartphone tilt to rotate the screen display. All three require measuring acceleration forces.

Common mistakes

Confusing accelerometer with gyroscope — gyroscopes measure rotation/angular velocity; accelerometers measure linear acceleration and tilt relative to gravity.
Not knowing laptop free-fall protection uses an accelerometer — IBM pioneered this with Active Protection System in ThinkPad laptops.
Assuming screen rotation uses only a gyroscope — while gyroscopes assist, the primary orientation sensing uses accelerometer data.

Exam tip

Accelerometer = detects linear acceleration + gravity direction. All three use cases: crash (sudden decel) + free fall (no gravity) + tilt (gravity angle). Gyroscope = rotation. Both are in modern smartphones. MEMS accelerometers are in virtually every electronic device.

Sources

NCERT Physics — Motion and Forces
MEMS Technology — Accelerometer Applications in Consumer Electronics

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