Q.Explain the meaning of heat and work with suitable examples.

Step 1. Heat is defined as the energy that flows from a body at higher temperature to a body at lower temperature, purely because of that temperature difference; once the flow stops, the term "heat" no longer applies -- a hot object should never be described as "having more heat," only as "having more internal energy" or simply "being hot." Example: a hot cup of coffee left on a table transfers heat to the surrounding air until both reach the same temperature; the coffee cannot be said to "contain" heat afterward.

Step 2. Work, by contrast, is a way of transferring energy between a system and its surroundings through a macroscopic, organised action -- pushing a piston, stirring a paddle wheel, or rubbing two surfaces together -- and crucially, it does NOT require the interacting bodies to be at different temperatures. Example: rubbing your hands together raises their temperature purely by mechanical work (friction), even though both hands start at exactly the same temperature.

Step 3. Both heat and work are process (not stored) quantities, measured in joules, and both are ways the first law's $\Delta U=Q-W$ can change a system's internal energy -- heat flowing in or work done on the system both raise $U$; heat flowing out or work done by the system both lower it.

Contrast the two using one example each: heat via a cooling object, work via rubbing hands or a piston.

• Describing an object as 'containing' heat -- neither heat nor work can be stored; only internal energy can.
• Assuming work always requires a temperature difference like heat does -- it explicitly does not.