It means that if you had a cubic meter of water it would weigh 1000 kilograms
A free electron is one which has become detached from a covalent bond between two atoms and is able to move around from atom to atom and possibly take part in electric current flow.
Gravity is a non contact force , jump from a little high place (don't do that :P) , you wont just get stuck in the air you will fall down , this is gravity you dont need any contact
The energy bar eaten by Sheila has chemical energy locked up inside it. This chemical energy is converted to mechanical energy in form of potential and kinetic energy and this in turn is converted to heat energy as the run progresses. Thus, the energy changes are: chemical energy to mechanical energy [kinetic and potential] and finally to heat energy.
