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Design and Make a Model Arm

Design and Make a Model Arm

Introduction: (Initial Observation)


We use it every day and probably do not even think about how it works. The human arm is a complex structure made up of bones, joints, ligaments, and muscle. But how does it all work? What makes us pick up that cup of coffee or throw that football to an exact area fifty yards away? This project will go deep into the human arm and how it works.

In this project, you will be designing your own model arm. You will also learn the parts of the arm and their functions.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about the human arm and how it works. Read books, magazines or ask professionals who might know in order to learn about the function of bones and muscles in the human arm and hand. Keep track of where you got your information from.

The following are samples of information that you may find.

One way to understand how an animal learns to control its motor system is by hypothesizing a model and comparing its behavior to that of the animal. Such a model will consist of three components: a detailed model of the animal’s musculoskeletal system, a dynamical simulator to model the physics of motion, and control architecture. Recent work in biomechanics has provided a precise musculoskeletal model of the human upper limb. It is composed of an integrated skeletal and muscle model derived from CT tomography data of a human male cadaver; the model consists of seven bones with 13 degrees of freedom and 42 muscle bundles representing 26 muscle groups.

What Are Joints?

Joints are the places where two bones meet. There are many different types of joints, some are movable and some are not. For example, the bones of the skull are held together by joints which cannot move. Most joints are freely movable, and are called synovial joints. Covering the ends of the two bones making up the joint is a layer called the synovial membrane. This membrane secretes a lubricating substance called synovial fluid, which helps the joints move and rotate more easily. There are six types of synovial joints:

    • Pivot – A ring of bone rotating around another bone. For example, the neck.
    • Ball-and-Socket – Allows movement in all directions. For example, the shoulder joint.
    • Hinge – Allows the joint to bend and straighten, but does not rotate. For example, the elbow joint.
    • Ellipsoid – A less flexible version of the ball-and-socket joint. For example, the wrist joint.
    • Saddle – Fit together to allow all movements except rotation. For example, the thumb joint.
    • Gliding – Two generally flat surfaces gliding over each other. For example, the joints between the tarsals of the foot.


Question/ Purpose:

The objective and purpose of this project is to understand the structure of the human arm and how it works.

Some sample questions are:

Contraction of which muscle will rise the forearm?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
This is a display project so you will not have to define variables. However, variables that can be studied using a model arm are as follows:

Independent variable is arm muscle. Values are Biceps and Triceps.

Dependent variable is arm movement.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
Contraction of Biceps will rise our forearm.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment: Create a model of the human arm

Introduction: Using household material or items that you can easily find, create a model of the human arm. Also, create a poster of a detailed diagram of the arm, which includes the major muscles, joints, and ligaments.


    • 3 cardboard squares (2 squares equal in length to lower arm, 1 square equal to length of upper arm)
    • tape
    • large paper clip
    • two long balloons
    • string
    • Adult to help you poke holes for the paper clips


1.Cut 2 cardboard squares equal to the length of your lower arm. Cut 1 cardboard square equal in length to your upper arm.
2.Roll the cardboard squares tightly, and bind the ends with tape.
3.Label your rolled squares. Label the one square that was equal to your upper arm -humerus. Label the other two squares-radius and ulna.

4.Make a hole through all three “bones” with something sharp. (An adult will need to help with this step.)
5.Unbend a paperclip. Thread it through the holes. Loop the ends.

6.Using your tape, attach the radius and ulna together by wrapping tape around the free end of both.
7.Slightly inflate two long balloons. Tie knots in both ends.
8.Tie on the balloon muscles. The first muscle will be the biceps. It is attached from the humerus to the radius.
9.Now tie on the balloon for the triceps. The triceps is attached from the one end of the humerus to the other.
10.Name the parts of your arm model. Compare the model to your arm.
11.Following images show the steps of constructing a model arm with some differences from what is discussed above. You can make additional changes as you may feel appropriate.

Some Sample Images:


For bones I rolled up heavy paper and used tape to keep them rolled like a tube. I then used paper puncher to make holes where bones join each other.

To give additional strength to the tubes, I inserted some Styrofoam in the tube specially where muscles are being connected later.

To connect the pieces I used fasteners. These are brass pieces with a head and two strips or blades that enter a hole. You fasten them by pushing the strips in opposite directions. I then cut and shortened the strips.

I also cut a hand from a piece of cardboard. As you see forearm has two bones (Ulna and Radius). From one side these two bones are connected to the bone in the upper arm (Humerus), and from the other side they are attached to the wrist.

Now is time to place the muscles.

I used twisty balloons for muscles. These balloons are very long and we can easily wrap their uninflected parts around the bones.

I used red and larger balloon as Biceps and the smaller (less inflated) orange balloon as triceps.

To connect balloons to the top of Humerus bone, I made two cuts on the top of the paper roll that can hold the balloons from their knot.
I then applied some additional tape to keep the role secure.

The same model can be constructed with wood dowels. In that case you will need someone to help you with drilling the holes on the wood. Everything else would be the same.

This is another smaller model arm made of wood dowels. Muscles are just rubber bands.

Instead of fasteners, paper clips are used to connect these pieces together. This also required drilling some holes.

Observation/ Discussion

    • Bend your arm up and down. Observe the muscles. What happens to the biceps as you move your arm.
    • This model arm has only two muscles. Does a human arm only have two muscles? (No, a human arm has many muscles. The biceps and the triceps work as a team. They work to make opposite actions happen.)
    • What kind of joint connects the humerus to the radius and ulna? (hinge joint)

More Challenges (optional)

    • Dissect a long bone. Visit the butcher at the grocery store and ask them to give you a bone that has been cut in half lengthwise.
    • Look at your bone and see if you can find the following: bits of muscles or tendons, marrow, blood vessels, and tiny holes in the bone for blood vessels.
    • There are four basic types of bones. Find out what the types are and where they are located.There are three basic types of muscles. Find out what the types are and where they are located.There are four kinds of joints. Make a model of each type.

Label Muscles and Bones:

Muscle in the back of your upper arm is called Triceps

Muscle in the front of your upper arm is called Biceps

The bone in the upper arm is called Humerus.

Forearm Muscles

Forearm bones are called Ulna and Radius

Additional project ideas

Mechanical arm

Mechanical arm is a devices that let you reach to a distant place and grab or relocate something. It can be used to pick up garbage from the ground without having to bend over. It can also help you to reach up high to pull or pick something.

Students may make a simple model of mechanical arm using a long wooden stick known as wood molding. The length, the dimensions and how you connect them are optional and may be performed in many different ways. The above diagram shows a long wooden stick in brown color with a handle attached to that using wood glue.

The jaw (painted red) may be cut from Plexiglas or wood. The green rubber band keeps the jaw closed unless you pull the wire or string. The other end of the string is formed like a ring to simplify pulling the jaw using your finger. The jaw is mounted on the end of the stick using a nail. The hole in the jaw is bigger than the nail so it can swing. The jaw can also be made by bending and forming a steel wire.

This is a craft and engineering project and you may have to utilize the tools and the materials you find around. Your project advisor cannot provide you with any additional information or support about a mechanical arm.

Materials and Equipment:

Use household materials. Basically, anything that you can think of to use to create your model arm. Be creative. Wood, cardboard, string, nail, etc. Following is just a sample list of what you need:

    • 3 cardboard squares (2 squares equal in length to lower arm, 1 square equal to length of upper arm)
    • tape
    • large paper clip
    • two long balloons
    • string
    • Adult to help you poke holes for the paper clips

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


If you do any calculations, write your calculations in this part of your project guide.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
There are four kinds of bones in your body. The bones of the arms and legs are called long bones. The bones of your body are connected with different types of joints. The joints allow your body to move in several different ways. The joint at your elbow is called a hinge joint. Connected to your bones are muscles. Muscles contract, or get shorter, to help you move. Muscles work in teams. Every set of muscles has an opposite set of muscles. This helps you to “reverse” or go in the opposite direction.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

    • How many different kinds of joints can you find on your body?Where are the different types located?
    • Draw the bones of the arm in the proper location on your body outline diagram. Label the bones. Draw the muscles attached to the arm. Label the muscles.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.