強い and 弱い: strength, resistance, and ability
Use context to interpret 強い and 弱い across physical force, resistance to weather or stimuli, ability in a field, and the intensity of a smell or effect.
Strong or weak force and structure
強い describes powerful people or objects and forces with high intensity. 海から強い風が吹いてきました。 refers to the force of the wind, while このロープは強くて切れにくいです。 refers to the durability of a rope.
弱い can describe insufficient power or durability. この傘は風に弱いので、嵐の日には使えません。 says that the umbrella cannot withstand wind well. The relevant standard for weakness depends on the object and condition in the sentence.
Strong in a field or weak against a stimulus
A field of knowledge or practical ability can be marked with に in expressions such as 数学に強い and 機械に強い. These describe competence in the field rather than physical muscle strength.
辛い食べ物に弱い and 寒さに弱い describe low tolerance for spicy food or cold. 弟は辛い食べ物に弱く、少し食べただけでも汗をかきます。 makes the reaction and the relevant stimulus clear.
Intensity of a smell or effect
この香水は香りが強いです。 and 薬の効果が弱いです。 apply the pair to the intensity of a sensation or effect. Naming 香り or 効果 makes clear what is strong or weak.
Not every contrast translated as strong and weak uses 強い and 弱い. 濃い and 薄い are often more natural for concentration or color. Identify the property being compared instead of relying on one translated word.
Quick check: Does この傘は風に弱いです mean that the umbrella produces only a weak wind?
Show the answer and why
No. It means that the umbrella has low resistance to wind and cannot withstand strong wind well. に marks 風 as the condition against which it is weak.