gravity: pebbles and ropes?

I currently teach piano at a small music school.  My students are ages 5-8 and mostly complete beginners.  While they are adorable and [for the most part] obedient students, it's hard to explain abstract concepts in concrete ways they will understand!  Take, for example, gravity.

gravity
In the context of piano, besides the fact that when you sit down you stay down and don't float back up, this applies to how you have your arms.  You should allow the natural weight of your arms to help them to rest gently on the keyboard.  When playing, you use the weight from your shoulder down through your fingertips.  You shouldn't force your fingers down from the first joint.

using examples
The only way to explain this to a young child is through visuals and analogies.  The first time I tried to do this with a six year old, I asked her if she had ever thrown a pebble into a pond.  She responded by shaking her head.  City kids!  So the idea of watching a pebble sink into a pond didn't ring a bell.

Next, I tried using the method book's illustration. (I use Faber and Faber's Piano Adventures with most of my students.)  Their visual is to imagine your arms as heavy, wet ropes.  That's all good and well if you've been near or have touched heavy, wet ropes, but again what city/suburbs kid has??  Unless you're awesome or crazy enough to bring in a bucket and ropes to the lesson (I know someone who has, props), that's not a very helpful picture.

eureka?
Finally, during a conversation with another musician, I hit upon the idea of demonstrating gravity with my own (or the student's own) body.  I asked my student to stand up and jump and tell me what happened to her body.
"It comes down," she said after jumping several times.
"Exactly!  So that's what should happen to your arms, too.  If your arm is totally relaxed and I'm holding it up for you, when I let go, your arm should drop right down," I replied, hoping that something was clicking.
And it did - we did a couple of dead arm drops and she was doing pretty well.
Then we went back to the piano.  As soon as she put her hands on the piano and set up her curved hand shape, her arms became rigid and her shoulders tightened up.  I reminded her to keep her arms heavy and she pushed them down.

With another student, we had trouble with the concept of a smooth drop.  She would do a wrist lift and come down to keyboard level, stop, push her wrist down and then try to play.  Which of course, didn't work too well.  I asked her to get up and jump again and asked her if she came straight down or if she stopped halfway.  She answered correctly, but the concept just wasn't translating to the keyboard.

Sigh.  I guess I will just have to wait patiently and persistently, or else find more new ways to explain the concept of weighty arms.

Thanks for reading!

cheers,
Serfy