Define, in your own words, what energy is and provide two examples of systems; one with kinetic energy and another with gravitational potential energy. Match the terms to these two groups (letter-number):

a) Combustion of diesel ; b) Friction between a match and sandpaper ; c) A bee flying ; d) A plane that took off a minute ago ; e) A pole when it is completely bent.

1) Kinetic energy ; 2) Elastic potential energy ; 3) Mechanical energy ; 4) Chemical energy ; 5) Internal energy