Trampolines is perfect to show true physics. When you jump you can calculate vi, vf, d, a, and t. While standing flat on the surface you can draw a free diagram. There would be an arrow pointing down to represent mg and an arrow up because you are perpendicular to the surface. What makes you slow down when you jump? When you bounce down to the trampoline, it absorbs some of your momentum. This reduces your momentum and that'll lead to a decrease in your velocity. If you jump with greater speed and force, you will have a larger jump.