Hammocks are super comfortable and fun but i didnt know that there is physics in a swinging hammock. In this picture Amanda and i are swinging unusually high because some of our teammates were pushing us (later on we actually flipped the hammock because we were going super high then someone tried to jump on. good times). This is an example of resonance. The people pushing us are the driving force, and are pushing at the driving frequency. When the driving frequency matches the natural frequency of an object its called resonance. Natural frequency is the frequency at which an object wants to vibrate. Resonance requires good timing rather than a lot of force.
ohyeah & squeezing 6 people in a hammock & trying to swing as high as you can is NOT a good idea. The hammock gets stretched & people fall out. Just dont be the person on the edge/sides or top.