Objective 5:

1.  They use the thermal energy by making the gas getting bigger inside of this cylender shaped thing.  This makes this thing called the pistol to go downward causing there to be a spark which then lights the spark plug.
http://www.ehow.com/how-does_4926292_car-engine-piston-work.html
http://wiki.answers.com/Q/In_a_heat_engine_what_happens_to_thermal_energy_that_is_converted_from_chemical_energy
2. They are alike and different becuase of what it this says "In an internal combustion engine, a working fluid is heated and expanded to produce power, captured in a cylinder and piston or in a turbine or similar system, and this heating and expansion is produced by burning fuel inside the expansion chamber. In an external combustion engine, the working fluid is heated by burning fuel, then introduced into the expansion chamber to produce power." from http://wiki.answers.com/Q/Difference_between_internal_combustion_engines_and_external_combustion_engines.   This basically means that the external one makes power by fluid being heated up while the internal one is made by a fluid that is heated and expands to make power.
http://wiki.answers.com/Q/Difference_between_Internal_combustion_and_external_combustion_engine
3.  I think that most likely (even though I now nothing about cars) that the external one could be a little bit dangerous becuase it is done by burning fuel which could be dangerous.
4.  What happens it all the hot air is sucked out causing it to be very cold inside of it.
5.  It would effect it because then all of the hot air would stay in there and cause everything to be getting hotter.