**Here are some examples of using the word «hardness»:**
1. The hardness of the rock made it difficult to drill through it.
2. She tried to hide her disappointment, but her eyes betrayed the hardness in her heart.
3. The hardness of his criticism hurt her feelings.
4. The hardness of the water in this area causes scaling on pipes and appliances.
5. The hardness of the competition forced him to work harder to achieve his goals.
6. The hardness of the ice made it impossible to skate on it without slipping.
7. The hardness of the situation required a strong and decisive approach.
8. The hardness of her gaze made him feel uncomfortable.
9. The hardness of the mattress made it difficult for him to sleep.
10. The hardness of life in the slums forced him to grow up quickly.