A magnitude does not need a line. For example,,temperature can increase and decrease in magnitude but has no defined direction ,, it is a chacteristic at a given point.
When you are traveling in a circle at a constant speed, there is no "line" involved as your direction is constantly changing...
Here are a couple of simple problems that when people overthink them they are easily stumped.
1. If you have a room that is 100% thermally insulated at a comfortable temperature of say about 70 deg F, then you introduce a refrigerator into the room and it is running with the door open...
At standard atmospheric pressure, usually accepted as 14.7 psi, at 100 deg C. water boils and steam condenses simultaneously, 100 C is the max temperature water can reach at this pressure and it is the minimum temperature that steam can exist at this pressure. Therefore it is possible for steam...