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  Investigate How can you make a model arm?
  Muscles help you move. Your biceps and triceps are a pair of muscles that help you bend your arm at the elbow. When you contract your biceps, your arm bends. To straighten your arm, you contract your triceps.
  Materials What to Do  
  Follow the diagram on the Model
Arm Pattern to make a model arm.
Make 6 holes in the cardboard.
Use a fastener to hold the 2 pieces
of cardboard together.
  Thread yarn through the other
holes. Tie 2 knots.
   
  Model Arm Pattern
  cardboard
  hole punch (optional)
  fastener
  biceps  
  Make your model arm
bend at the elbow.
    Tie a knot.
 
triceps
  yarn
  When you use
cardboard and
yarn to show how
an arm moves, you
make a model
of an arm.
  Tie a knot.
  Move the model arm by pulling one piece
of yarn. Then put the arm in its original bent
position. Make it move again by pulling on
the other piece of yarn.
Observe how the model
arm moves when you pull each string.
   Compare your model
   to your arm.
  Record what you observe.
  String Pulled How the Model Arm Moved  
  Biceps
string pulled		    
  Triceps
string pulled		    
    Explain Your Results
 
1.
 What happens in your model when you
pull each piece of yarn?
 
2.
 How are your model and a real arm
alike and different?
  How can you make a model
that shows how the muscular
and skeletal systems work
together in the leg? Make a
plan to find out.