Wow, we had quite a turn out this Saturday to learn about elbows and muscles. Thanks everyone for coming!
I repeated the Elbows and Muscles lesson I did at Kid's Day since I had leftover material (and it's a fun one!). The detailed instructions on how to make the elbows are here: younger kids elbow lesson, while the more advanced lesson can be found here: middle+high school elbow lesson.
Since the science days are attended by neighbor hood preschool aged kids, I decided to add a new trick to help with conceptualizing how muscles really work.
I tied a string to a rock.
I then asked the kids to move the rock with the string (9 times out of 10 they intuitively pulled the string towards them). I then asked them to push the rock to me using the string. It never worked! Strings don't push, they only pull.
Then if I still had their interest, we continued on to making elbow models (lessons described in the above links). Some kids, depending on their interest level, got anatomy lessons about the bones and muscle names (major muscles: biceps (flexion/bending), triceps (extension/straightening); arm bones: humerus (upper arm), radius and ulna (lower arm)). We also brought up tendons, which attach muscles to bones (our string muscle was attached to our ruler bone with a paperclip "tendon").
One participant had an awesome question about making a punching motion. Punching motions use more than one joint! I discussed the way the shoulder moves (many, many degrees of freedom) that helps you raise your arm forward and pull it back, combined with the bending/straightening of the elbow (+rotational degree of freedom of the radio-ulnar joint) helps you punch. To model this, you would need two more joints on top of the basic flexion/extension elbow we just made. Your body has many muscles, bones, and joints that work together as a team to move you in the way you'd like to move.
P.S. To the parents: I don't endorse nor did I come up with the idea of the karate chopping elbows. Sorry if your kids have figured out they can sock their sibling with the elbow model.
Link to bulk purchase of rulers: Charles Leonard Inc. Ruler, 12 Inch, Wood, 36 rulers