惰性(だせい)

惰性(だせい) describes continuing without active effort, either physical momentum or habitual behavior.

Writing

• 惰(だ) (lazy, idle)
• 性(せい) (nature, tendency)

Sense 1 (PHYSICAL)

• Physics term for inertia/momentum
• Objects continuing in motion
• 惰性(だせい)で走(はし)る (coast, roll on momentum)

Sense 2 (HABITUAL)

• More common usage
• Doing things without thought or enthusiasm
• Often negative connotation (implies lack of motivation)

Common expressions

• 惰性(だせい)で (out of habit, on momentum)
• 惰性(だせい)に流(なが)される (to be carried along by inertia)
• 惰性(だせい)で続(つづ)ける (to continue out of habit)

Common collocations

• 惰性(だせい)で仕事(しごと)をする (work out of habit)
• 惰性(だせい)で付(つ)き合(あ)う (date out of habit)
• 惰性(だせい)に負(ま)ける (give in to inertia)
• 惰性(だせい)を断(た)ち切(き)る (break out of routine)

Usage

• Usually implies lack of passion or purpose
• Suggests need for change or reflection
• Common in self-help and motivation contexts

Related words

• 慣性(かんせい) (inertia - physics term)
• 習慣(しゅうかん) (habit - more neutral)
• マンネリ (being in a rut)

Register: Neutral. Common in both casual and formal contexts.