Why does a flat clover-like shape fall slower when it is rotating? The plastic flat clover-like shape pictured below falls noticeably slower when it is rotating fast.  I wonder why.  Its three edges are flat, so I don't think that the rotation makes it act like a propeller.  An ideal explanation would include an analogy that a young child can understand (e.g. rain bouncing on a car's wind-shield).
Here is a photo of the object. 
 A: Air has momentum.  Put another way, it takes air some time to get out of the way.
When the blades are rotating fast enough, they approximate a disk for the purpose of air resistance.
You can prove this is not a propeller effect by pitching the blades as in a propeller.  When dropped, the propeller will start rotating so as to "screw" itself thru the air downwards.  However, the object will drop noticably slower once it is spinning.  If it were only a propeller issue, it should drop faster once the propeller is rotating in the direction to make the object go down.  The reason it doesn't is because the propeller blades together approximating a disk adds much more air resistance than the bare blades by themselves.
There have been aircraft built on this principle.  Look up something called a auto-copter or auto-gyro.  These use freely-rotating blades to form a disk-shaped wing.  They look a lot like helicopters, but in a helicopter the rotor is powered and the propeller effect used to create lift (at least when hovering or vertical flight).  In a auto-copter, somethine else, usually a traditional pushing or pulling propeller, is powered, but the vertical-axis rotor is free spinning.
This effect is also exploited to land a helicopter when the engine dies.  When the engine is powering the rotor, the blades are pitched so that the air is pushed down.  You can think of the blades trying to "screw" upwards thru the air.  When the rotor becomes free-turning, they have to be pitched the other way to "screw" dowwards thru the air so that the downward motion of the craft causes the rotor to keep spinning.
There is a optimum pitch angle for the blades.  Too little, and there won't be enough torque to keep the rotor spinning.  Too much, and the "gearing" is too low such that there isn't enough spin per unit drop.  Close to the ground, the blades are pitched upwards again.  The momentum of the spinning blade is harvested to actually provide a propeller push upwards, or at least a nearly flat pitch.  The momentum is spent quickly, so it takes a lot of skill to do this at just the right time.
A: There is an amount of lift that each blade gets, and it depends on the angle at which the air hits the blade.
When you just drop the toy, the air hits each blade directly at 90 degrees.
In that case, all you get is drag.
In airplane terms, the blade acts like a stalled wing.
It's more like a parachute than a wing, and it's not really big enough to make a very good parachute.
However, when it's turning, the air is coming up, and the wing is moving forward fast enough so that the air hits the wing at a shallow angle.
When this happens, the blade actually has lift.
In airplane terms, it's like gliding, at sufficient speed that the angle of the air against the wing has the wing acting like a wing, not like a parachute.
In that case, it will fall more slowly.
It's exactly the same in an airplane.
If the speed of your glide is above stall speed, you come down slowly.
If the speed is below stall speed, you come down quickly and out of control.
Every airplane has a stall warning horn, and every pilot is trained what to do.
When that goes off, you shove the nose down to reduce that angle, and pick up speed.
Even if you don't want to, because you're close to the ground, it's your only hope.
Fortunately, most airplanes, if they're properly loaded, are very resistant to stalling, because if they get too slow, they automatically drop the nose.
