How can you use your centre of gravity to help you jump higher?

Question

i was reading this article on basketball http://www.wikihow.com/Dunk

and apprently if you lower your centre of gravity whislt u enter in for your plant,therefore having a lower centre of gravity when u go to jump,and it says u can gain up to 7 extra inches of vert from doing so!!

so can any1 out there help me by telling me if this is true,how it works and is there a particualr method tht works the best

Answer 1

Lowering your CG will give you an extra bit of spring time (dt) to increase your impulse I = Fdt = dp = m(v1 - v0) = mv1.  F is the force you push off with; we assume it's some fixed value based on your strength and personal conditioning.  dp is the change in momentum, which is also called impulse.  m is your body mass, v0 = 0 the initial velocity while in the crouch, and v1 is your velocity as your feet leave the floor.

Spring time is the interval of time (dt) between startiing your jump from a crouch to the time your feet leave the floor.  This in turn will give you more v1 for the same force F.  v1 is the velocity you leave the floor with after being v0 = 0 in your crouch that lowers the CG.

From  KE = 1/2 mv1^2, which is the kinetic energy equation, you can see that a greater v1 will give you more  KE upon leaving the floor.  That KE is converted into potential energy PE = mgh; where h is your max height.  From the conservation of energy law, we can write KE = 1/2 mv1^2 = mgh = PE, which means all your kinetic energy is converted to potential energy at the top of your jump where your vertical velocity is momentarily once again zero.

Solve for h = v1^2/(2g) and now you can see why crouching lower will give you more height.  That is, the lower crouch will give more spring time (dt), which in turn yields more v1 velocity.  g = 9.81 m/sec^2 on Earth's surface (or 42" off the hardwood).  

Look at the equation carefully.  It says that the height attained off the floor is proportional to the square of the jump velocity.  Thus, a little bit of increase in v1 can have a greater increase in height of jump h.  If you use the equations here, you can actually calculate how much more dt you'd need to jump that extra 7 inches.

But, and this is a big BUT...a longer dt to get that extra 7 inches means you are at longer risk of having that ball blocked.  That results because your crouch puts you within easy reach of the defenders.  So, there you are, do you want to risk the blocked shot for a longer period of time to gain that extra 7 inches of jump height?

There is another option to gain that 7 inches.  Remember dp = Fdt = mv1; if you keep dt the same, i.e., don't lower your CG, but increase F, the force of your push off, you can also increase v1 and do so without increasing that period dt where the ball might be blocked.  But increasing F means exercise, good diet, and all that practice needed to improve your strength and conditioning.  In other words, good hard work; something all the great roundball players have learned and practice.

Answer 2

I surmise you are referring to this tip:

"For people who have trouble jumping off one foot, try this: as you approach the basket, lower your body and arms so that your center of gravity is low. Then, explode toward the basket and swing your arms up. This could improve your one-footed jumping ability by several inches."

By doing as suggested, you build more momentum so that more energy is applied to your jump. Think of it like throwing a baseball. If you stand flat-footed and throw, only the mass of your arm provides the energy. Now wind up, lean back and throw. More of of your body's mass provides the energy.

I hope that made sense.