Suppose you plan to take a hot water bath on a cold morning. Explain this observation : when you initially enter the bathtub the water feels very warm, but after sometime it seems as it the water is not as warm as it was earlier although temperature of the water is same?
When you enter the tub initially, the temperature of your body is considerably cooler then that of water. Hence the water seems to be very hot. But after sometime heat transfer takes place and there tends to be a thermal equilibrium between the water and your body, hence the water feels normal after sometime.
This question give a little bit more insight to a very trivial everyday phenomenon using the concepts of Newtonian Mechanics and Non Inertial frames. When you are standing in a bus and driver suddenly applies brakes, you tend to fall forward. How would you explain this situation, using First Law (Law of Inertia) or since the bus has a deceleration you will use a Non Inertial frame?
This situation can be explained both by using Law of inertia and also by using a Non Inertial frame, BUT the frame of reference considered in both the cases would be different. For using Law of inertia, you have to take earth as the reference frame and then you can say that when the brakes were applied, the man in the bus was already having some motion and according to Law of inertia man's body would tend to oppose any change in its motion. For using Non inertial frame, we take our frame of reference to be inside the bus. In this frame, to apply Newton's laws, we have to show a pseudo force(in the forward direction). And hence in this frame, we can say that the man fell forward due to the pseudo force that comes in this frame.
What does this code fragment do? (given ch is declared as int): if ( (ch = getchar() ) >= '0' && ch <= '9') printf ("%d\n", ( ch - '0' ) * ( ch - '0' ) ); ?
This answer assumes that you know about the if statements and functions in C programming. So, first of all we need to know about the getchar() function. This function takes a single character from the standard input, In the code above, since ch is declared as an int, the ASCII value of the character entered will be stored in ch. Now, if that value is between the ASCII values of 0 and 9, then the printf statement will be executed. Since the ASCII value of 0 is 48, ch - '0' will be the number entered itself. So this code snippet simply prints the square of the number entered.