Doing Melachah
14. In a place where the minhag is to do melachah on Tishah B’Av, one may do melachah; in a place where the minhag is not to, one may not (שו"ע תקנ"ד סכ"ב). The reason for the minhag not to do melachah is to ensure that we do not lose focus of the aveilus. Today, the universal minhag is not to do melachah, at least until chatzos (ביאה"ל בשם מטה יהודה).
15. Conducting business for profit is included in the issur melachah.
16. One may do a melachah which does not take up time since it does not distract from the aveilus (מ"ב שם סקמ"ג ). Accordingly, one may seemingly send a single email if it is urgent or do something very minor and quick on a computer. Still, a yerei Shomayim should be machmir to avoid everything (ח"א כלל קל"ה ט"ו ) so that he is not distracted from the aveilus.
17. Grocery store. One may open his store to sell staples such as bread, milk, and the like for children and others who are not fasting, as well as for after the fast (כף החיים סקק"ו ).
18. Tishah B’Av day camps. One may organize a Tishah B’Av day camp for local children, even for pay. This is not a problem of business on Tishah B’Av since it is a necessity, as it makes it much easier for parents to fast and mourn properly.
19. Other than construction or other loud work, one may have a non-Jew do melachah for him even in his house (מ"ב מ"ו ).
Greeting People
20. One may not ask someone else how he is doing on Tishah B’Av (שו"ע תקנ"ה ס"כ ). Similarly, one may not say “Good morning” (מ"ב מ"א ). One may wish “Mazel tov” on a simchah since that is just a brachah. One may also wish someone “Refuah sheleimah” (גשר החיים פכ"א ס"ז אות ז').
21. One may answer “Hello” on the phone since that is not a greeting as much as a way of answering the phone (ע' שו"ת באר משה ח"ז סי' ל"ג וח"ד סי' ק"ו ), but one should make sure not to say “Shalom” on the phone.
22. For the same reason we do not greet people, one may also not send someone a gift. One may, however, send food for a friend or neighbor to have after the fast (שו"ת התעוררת תשובה ח"ג סי' שנ"ה ).
Sitting on the Floor
23. We sit on the floor in shul on Tishah B’Av night and day until Minchah [or chatzos (רמ"א )] (שו"ע תקנ"ט ס"ג ). One who finds it difficult to sit on the floor may place a sack or small cushion underneath him or sit on a low bench (מ"ב סקי"א ).
24. A person who is ill, elderly, pregnant, or cannot sit on a low seat for some other reason may sit at a regular height (ערוך השלחן יו"ד סי' שפ"ז ס"ג ).
25. The person who does hagbah on the sefer Torah (דרישה יו"ד שפ"ד אות ב') and the sandek at a bris may sit on a regular chair.
26. Some poskim hold sitting on the steps in front of the aron or bimah is considered sitting on the floor (מקור חיים לחו"י סי' מ"ג סס"א ). However, others point out that the Maharil specifically sat on the floor, not on a step in front of the aron (באר היטב תקנ"ט סק"ג ).
27. On a bus. When traveling on a bus or train, one does not need to stand throughout the ride since his intent in sitting is for safety reasons, not for pleasure or comfort (טעמא דקרא בשם החזו"א ).
