Think about a rollercoaster. If it loaded at a height of about 500m and then dropped down to almost ground level and was followed by 7 circles where the circles height was about the same it would not work well. Explain in terms of kinetic energy, potential energy, etc. why not.
(Picture included if needed.)
If the circle's heights were the same, then eventually the friction would cause enough energy loss so that the decrease in energy would not give it enough kinetic energy to overcome the height (potential energy) of the the loops.
If the loops were smaller, then it might work... ...
The answer is explained in approximately 100 words and a reference is provided.