Pictograph with debated etymology: either a flexed arm muscle in profile, or an ancient plow / farming tool. Either way, "physical force / strength". The abstraction "power / energy / capability" grew from this physical anchor. Identical across 繁體 / 新字体 / 简体.

力 is one of the foundational radicals — it appears in many strength-and-effort characters: 男 (man, "field-power" — already in earlier batch), 加 (add), 助 (help), 努 (strive), 勝 (victory), 動 (move), 勉 (encourage / strive), 勇 (brave). When you see 力 inside a character, expect physical or moral force.

Mandarin: lì, falling 4th tone. 力 anchors a wide vocabulary of effort and capability: 力气 (lìqi, physical strength — neutral final tone), 努力 (nǔlì, to make effort — extremely high-frequency word), 能力 (nénglì, ability / capability), 实力 (shílì, real strength / capacity), 压力 (yālì, pressure / stress — modern term for psychological pressure), 暴力 (bàolì, violence), 重力 (zhònglì, gravity — physics).

Japanese: TWO on-readings. リョク (ryoku) is dominant — 努力 (doryoku, effort), 実力 (jitsuryoku, real ability), 能力 (nōryoku, capability), 体力 (tairyoku, physical strength), 協力 (kyōryoku, cooperation), 重力 (jūryoku, gravity), 電力 (denryoku, electrical power). リキ (riki) appears in 力士 (rikishi, sumo wrestler — literally "strength-warrior") and 馬力 (bariki, horsepower — note the playful kun-on hybrid). Kun-reading ちから (chikara) is the everyday word — 力 (chikara, strength), 力持ち (chikaramochi, strong person), 力を入れる (chikara o ireru, "put strength into" / focus effort).

力士 (rikishi, sumo wrestler) preserves the ancient warrior-strength sense — Japan's national sport names its athletes with this character.

Memory aid: a flexed muscle / plowshare — physical force becomes the abstract noun.