State the first law of thermodynamics.

Explanation

### Step-by-Step Solution:

1. **Definition of the First Law of Thermodynamics**:
The first law of thermodynamics states that energy cannot be created or destroyed; it can only be transformed from one form to another. This means that the total energy of an isolated system remains constant over time.

2. **Energy Transformation**:
The law emphasizes that energy can change forms, such as from chemical energy in fuel to mechanical energy in a vehicle. For example, when fuel (like petrol or diesel) is burned in an engine, its chemical energy is converted into mechanical energy that powers the vehicle.

...