Fingers of the Hand
10 Straws, fairly large diameter
String, small, like kite string
1 Paint paddle
10 Popsicle sticks
Saw or side cutters to cut paint paddle
Tape, white or black
A few bamboo skewers to help push the string through the straws
Cut three pieces of Popsicle stick about 1/3 of the length of a full stick. Cut three pieces of straw slightly shorter than the sticks.
Glue the pieces of straw to the Popsicle pieces. Put the glue on the Popsicle piece not the straw or the straw may melt. Do this to all three pieces.
Glue all three stick segments onto a full straw. The sticks should be sandwiched between the straws now. Leave a small space in between each segment, so that bending is possible at each joint.
Cut the full straw’s excess but leave enough to glue it onto a full length Popsicle stick. Glue one more straw segment onto the top of the full length Popsicle stick in line with the other three segments.
Tie a bead onto the end of piece of string. Use the bamboo skewer to thread the other end of the string through all four short straw segments.
Tie a bead onto the other end of the string. This is one complete finger. Wrap each segment with tape to reinforce the glue. Masking tape works but black tape looks nice. Alternatively, you can just use tape and no glue to avoid burns, but it is harder to hold the small sections in the correct position as you tape them together. Pre-bend the finger at each joint.
You should be able to hold the long stick and pull the string to make the finger bend.
The Whole Hand
Cut a paint paddle in half, then one half into two pieces, one about an inch shorter than the other. Glue the larger piece to the top of the full half of the paint paddle to form a T. Glue the smaller piece right underneath it.
Make three more fingers and a thumb. The thumb has one less segment than the other fingers. Glue the fingers to the paint paddle frame.
Glue on the thumb more towards the side of the hand. Each finger should move when pulling on its string.
A Bit More Info:
In science, models help us understand the real thing. A model is similar to the real thing, but every model has its limitations. As work with a model, you must always think about what is similar and what is different from the real thing.
We move our bodies by muscles pulling on bones. Bones attach to bones with ligaments. Bones attach to muscles with tendons. Most of the muscles that pull on each segment of each of our fingers are actually in our forearm. If you put your hand palm-up on the table and move one finger at a time, you can see narrow lengths of muscles move in the forearm. Each of these muscles is connected to one bone in the hand through long tendons. The tendons move from the arm to the hand through the carpel tunnel.
There are several major differences between this model and a real hand. In your hands there are actually three muscles going one each to the three bones of a finger. We usually use them all together, so many people are not able to move a single bone, say in the tip of a finger. Also, when we stop pulling a finger tight, it doesn’t snap back like the model finger does. We have another set of muscles and tendons going down the back of each finger that re-extends them on demand.
If a tendon breaks, sometimes you can repair it. Ligaments are much more difficult to heal. The ligaments in this model are the long straws connecting the bones in the back of the finger. Muscles, bones, tendons and ligaments always work together, and if there is too much force put on the system, any of them may break.
The Popsicle stick represents the bones in this project. They give the structure to the hand.
The strings represent the tendons in this project. They connect the bones to the muscles.
Your pull represents the muscles in this project. There are few muscles in the hand – the muscles in the arm pull on the tendons that make the hand move.
What are some differences between this hand and your hand?
Our hands have two sets of tendons, one in front of the bones and one in back. What are the ones in back for?
What happens if your tendons break?
Ligaments hook bones to other bones. What are the ligaments in this project?