D. an outside or unbalanced force acts upon the object.
For example, an internal combustion engine converts<span> the </span>potential<span> chemical </span>energy <span>in gasoline and oxygen into </span>thermal energy<span> which, by causing pressure and performing work on the pistons, is </span>transformed<span> into the mechanical </span>energy<span> that accelerates the vehicle (increasing its kinetic </span>energy<span>).</span><span />
