DIY arm model
Make your own functional hand model!
Warning! Only under adult supervision.
- 2 plastic bottles;
- 2 rulers;
- 2 balloons;
- paper straws.
Trace your hand and cut the drawing out. Use hot glue to attach some threads (tendons) to the fingertips and some pieces of straws (bones) to the hand. Pull the “tendons” – the hand contracts! Make a muscle: bore a hole in a bottle cap, insert a silicone tube, and tape a balloon to the short end of the tube. Make several long vertical cuts in the plastic bottle. Insert the balloon into the bottle and screw the cap on – the muscle is ready! Make a second one the same way.
Hold two rulers together and drill a hole in them. Pull a thread through the tendon’s ligament and glue the “hand” to one of the rulers. Make another hole in the ruler and pull the thread through it. Fasten the rulers with a bolt and nut, and fix the muscles to the rulers using zip ties. Connect the tubes on the muscles with a splitter and pass the thread from the hand through the bottom of the first bottle and tie a knot. Attach the bicep to the second ruler the same way. Blow into the tube, inflating the balloons – the arm bends!
As they inflate, the balloons force the bottles to widen, which causes them to shorten. The “tendon” attached to the bottom of the bottle pulls the “forearm” along! Let the balloons deflate – the arm will unbend. Human biceps work similarly: the muscle shortens as it contracts, and the tendon thus pulls the forearm upward, bending the arm.
More exciting experiments are waiting for you in the MEL Kids subscription!