The First Law of Thermodynamics

Question 1

Mechanical Work

Answer 1

Mechanical Work is energy that is transferred to an object which causes it to move. You know work has been done if it changes position, or changes shape.

Question 2

Conservation of energy

Answer 2

Energy is always conserved - energy can be added or removed from a system but never lost. Energy is added or removed, or transferred to or from the system by mechanical work.

Question 3

The first law of thermodynamics I

Answer 3

Delta U = Q + W

Q = +ve if heat is added
Q = -ve is net heat is removed

W = +ve if net work is done on the system
W = -ve is negative if net work is done by system

Question 4

The first law of thermodynamics II

Answer 4

Internal energy of an object increases if heat (Q) is added. Internal energy of an object increases if work (W) is done on the system

Question 5

Heat Loss in Mechanical Systems

Answer 5

In physics, we often talk about perfect system but in real life these don’t exist. In the real world, some heat will be lost to the surrounding environment. This means that the actual usable energy is less than the amount we calculate.