Hands-on Activity: Lending a Hand: Teaching Forces through Assistive Device Design

Contributed by: Inquiry-Based Bioengineering Research and Design Experiences for Middle-School Teachers RET Program, Department of Biomedical Engineering, Worcester Polytechnic Institute

Quick Look

Grade Level: 8 (6-8)

Time Required: 4 hours 30 minutes

(six 45-minute class periods)

Expendable Cost/Group: US $2.00

Group Size: 3

Activity Dependency: None

Subject Areas: Biology, Physics, Science and Technology

A photograph shows two hands manipulating a student-created prototype made of clear plastic tubing, tape and craft sticks. The prototype is gripping a plastic cup.
Copyright © 2015 Kelly Cox, science teacher, Holy Name Central Catholic Jr. Sr. High School, Worcester MA


Students learn about how biomedical engineers create assistive devices for persons with fine motor skill disabilities. They learn about types of forces, balanced and unbalanced forces, and the relationship between form and function, as well as the structure of the hand. They do this by designing, building and testing their own hand "gripper" prototypes that are able to grasp and lift a 200 ml cup of sand.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Biomedical engineers use their knowledge of biology, physics, math and technology to create biomechanical devices. Biomedical engineers create assistive hand devices by researching the anatomy, form and function of the hand and the necessary responses and movement required for performing basic and advanced functions (such as rotating the hand vs. the gripping of an object). In considering the qualities of the materials that can be used for the specified functions, students subsequently practice the skill of designing and testing prototypes within constraints—all essential aspects of engineering.

Learning Objectives

After this activity, students should be able to:

  • Explain how the engineering design process steps are conducted during each class.
  • Generate questions for client/user to focus on a problem statement.
  • Describe the interaction of forces acting on the prototype during testing periods.
  • Apply the EDP in creating prototype devices to aid children in holding a cup of sand, and test them for strength.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS Performance Expectation

MS-PS2-2. Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object. (Grades 6 - 8)

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This activity focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Plan an investigation individually and collaboratively, and in the design: identify independent and dependent variables and controls, what tools are needed to do the gathering, how measurements will be recorded, and how many data are needed to support a claim.

Alignment agreement:

Science knowledge is based upon logical and conceptual connections between evidence and explanations.

Alignment agreement:

The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change. The greater the mass of the object, the greater the force needed to achieve the same change in motion. For any given object, a larger force causes a larger change in motion.

Alignment agreement:

All positions of objects and the directions of forces and motions must be described in an arbitrarily chosen reference frame and arbitrarily chosen units of size. In order to share information with other people, these choices must also be shared.

Alignment agreement:

Explanations of stability and change in natural or designed systems can be constructed by examining the changes over time and forces at different scales.

Alignment agreement:

  • Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation. (Grade 6) More Details

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  • New products and systems can be developed to solve problems or to help do things that could not be done without the help of technology. (Grades 6 - 8) More Details

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  • Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation. (Grade 6) More Details

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  • Explain and give examples of how the motion of an object can be described by its position, direction of motion, and speed. (Grades 6 - 8) More Details

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Materials List

For the teacher's introductory presentation:

Each group needs:

For the entire class to share:

  • ~100 feet clear vinyl tubing (preferably ½" outer diameter, 3/8" inner diameter)
  • 1 box regular-sized craft sticks
  • 1 box jumbo-sized craft sticks
  • 1 roll duct tape
  • 1 roll masking tape
  • 10-lb. bag play sand
  • ~1,000 feet polyester string
  • 4-10 electronic scales or triple beam balances
  • 4-10 force meters or spring scales
  • 4-10 100-ml graduated cylinders
  • 4-5 6-8 oz. clear plastic cups
  • (optional) 4-5 tube cutters
  • (optional) dynamometer
  • computer and projector, to show the class the PowerPoint® presentation

Worksheets and Attachments

Visit [www.teachengineering.org/activities/view/wpi_lending_hand_activity1] to print or download.

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Pre-Req Knowledge

A basic understanding of types of forces, Newton's second law, and knowledge of drawing free body diagrams and the engineering design process (EDP). See the Fairly Fundamental Facts about Forces and Structures lesson.


If a person has trouble seeing, what is used to help them see? (Glasses) If a person has trouble hearing, what is used to help them hear? (Hearing aid) If a person has trouble walking, what is used to help them walk? (Cane or crutch) A pair of glasses, a hearing aid, a cane or a crutch—what do these objects have in common? They are all assistive devices, a product that helps someone perform a function that could not be done without that piece of technology.

Technologies like these are developed by biomedical engineers who integrate their STEM (science, technology, engineering and mathematics) knowledge, including the field of medicine, to create products and processes that improve the health and quality of human lives.

In this project, you play the role of biomedical engineers to design and test an assistive hand device that helps someone with cerebral palsy grip a cup that varies in weight.



Students should have read the Fairly Fundamental Facts About Forces and Structures lesson, which provides all necessary background information for this activity.

Before the Activity

With the Students

Day 1 – Introduce the EDP and Assistive Hand Device Challenge

  1. (slides 2-12) Instruct students to record notes from the presentation. These slides includes key vocabulary terms, the steps of the design process, and the criteria and constraints for the design challenge.
  2. Give students the Problem Statement Worksheet and, from the client statement, have students individually compose brief problem statements of essential information. Lead a class discussion to make sure all significant information has been identified.
  3. Hand out the List the Client's Criteria Worksheet, and have students identify the prototype requirements. Lead a class discussion to make sure all significant information has been identified.

Day 2 – Conducting Research

  1. (slides 13-19) Instruct students to record notes, including key vocabulary terms, the purpose of reverse engineering, and the expected structure of T-chart. (On the classroom board, demonstrate to students the intended structure and purpose of a T-chart. This information is not provided in the presentation.)
  2. Provide students with the Materials Cost Table & Budget Sheet so they are aware of the materials they are permitted to use in constructing the prototypes.
  3. Assign each student five vocabulary terms for which to record definitions and other relevant information. They submit this information to the teacher, who compiles it for sharing in a class discussion.
  4. Have students research the structure of the human hand as well as assistive hand device technologies. Direct students to make T-charts of the pros and cons of these technologies in consideration of the specified criteria and constraints. Require students' charts to include information about the structures and functions of existing designs. Students submit their information to the teacher for later use during a class discussion.

Day 3 – Budgeting, Brainstorming and Building

  1. (slides 20-22) Instruct students to record notes, including the key vocabulary term "budget" (slide 20) and the definition and guidelines for brainstorming (slides 21-22). Explain the requirements for purchasing materials—that students must fill out the materials for purchase on their budget sheets, so the teacher can sign off on the budget calculations before handing out materials.
  2. Assign students to groups of 3-4 students each. Direct the groups to brainstorm among themselves hand device designs (refer to Figures 1-3 for examples created by other student groups).
  3. Once teams have an idea of viable designs, they create at least three sketches, labeling the parts and materials to be used for each structure in the design.
  4. Groups who complete the minimum three sketches must reach agreement between all members to begin with one of the three sketches. These groups fill out their budget sheet and begin building.
    A photograph shows three different hand-device prototypes. All are made of duct tape and regular- and jumbo-sized craft sticks. Two of them also use clear plastic tubing and string.
    Figure 1. Three examples of student-created hand device prototypes.
    Copyright © 2015 Kelly Cox, science teacher, Holy Name Central Catholic Jr. Sr. High School, Worcester MA

Day 4 – Prototype Construction

  1. If groups did not start building by now, then it is time to select one sketch to start building the prototype today.
  2. Have groups fill out their materials budget sheet, obtain materials and construct prototypes.
    A photograph shows an assistive hand device prototype composed of four jumbo-sized craft sticks, cut in half and secured by duct tape. This piece is laid flat against a surface, representing the palm of a hand. Short, finger-like appendages, made by clear tubing pieces, are attached to the "palm' and are lifted by strings threaded through the tubular fingers.
    Figure 2. The fingers (clear plastic tubing) of a student's prototype are pulled by threaded strings.
    Copyright © 2015 Kelly Cox, science teacher, Holy Name Central Catholic Jr. Sr. High School, Worcester MA

Day 5 – Prototype Building, Testing, Communication and Redesign

  1. Have students record notes from (slides 23-28) the presentation, which includes key vocabulary and the EDP steps 4-8.
  2. Give each group 1 cup filled with 200 ml sand, and a second, empty cup. Each group tests its prototype by gripping the empty cup. Once they have succeeded in lifting the empty cup, they slowly pour the sand from the filled cup into the empty cup. Explain to students that this test is not exactly the same between groups, since the rate of sand being poured per second will differ between groups.
  3. Instruct students to communicate within their groups as to how the prototype performed, using key vocabulary terms (physics-based). Then students create new sketches that incorporate improvements to their design prototypes.
  4. Groups continue to build second prototypes, completing their budget sheets and obtaining materials as needed.
    A photograph shows an assistive hand device prototype composed of a long piece of tubing attached by duct tape to five shorter pieces of tubing. The represented forearm, wrist and middle finger each have string threaded through the tubing, which loops back through the thumb, to serve as a belt to hold the cup.
    Figure 3. A student's hand device prototype, designed to pull a string to tighten the grip around a cup.
    Copyright © 2015 Kelly Cox, science teacher, Holy Name Central Catholic Jr. Sr. High School, Worcester MA

Day 6 – Reflection

  1. Give each student the Reflecting on the Engineering Design Process Worksheet. Describe what is expected in filling out each part of this assignment.
  2. Give teams time to make final alterations to their prototypes. Walk around to each group and have them perform a final test. Have students to discuss within their groups how their prototype performed, discussing forces and using other key vocabulary terms.
  3. In groups, have students complete the rest of the EDP worksheet.


air resistance: Type of frictional force that slows down objects as they travel through air.

applied force: Force applied to (exerted on) an object by another object.

assistive device: A product that helps someone perform a function that could not be done without that piece of technology.

bending: An added force (not directly across from support forces) that causes compression on one side and tension on the other.

biomechanics: The study of the motions of a human body, especially of the forces exerted by bones and muscles.

biomedical engineer: An engineer who uses STEM and medical knowledge to create solutions that improve the health and quality of life for human beings.

client: Person who communicates to an engineer the criteria of a design challenge.

compression: Two pushing forces, directly opposing each other that squeeze an object to try to squash (or compress) it.

constraint: A limitation or restriction.

criteria: Standards against which something must be judged; minimum expectations assigned for a design.

engineering design process, or EDP: A series of steps used by engineering teams to guide them as they develop new solutions, products or systems. The process is cyclical and iterative.

friction: A slowing-down force; exerted by a surface as an object moves across it.

gravity: A force that pulls objects towards the center of the Earth; force that pulls objects towards some massively large object.

inertia: State of being at a constant speed in the same direction.

iterative: Being or becoming repetitive.

Newton's first law : An object at rest stays at rest, until acted upon by an unbalanced force. An object in motion stays in motion, until acted upon by an unbalanced force.

Newton's third law: For every action, there is an equal and opposite action.

normal: Support force; exerted perpendicular to the surface of a stable object.

reverse engineering: The process of conducting research on how some solution (object or process) works; to understand what works well and what doesn't work well.

shear: Two pushing (or pulling) forces opposing each other, but not directly across from each other.

tension: Two forces pulling in opposite directions; the force used to stretch an object by pulling it apart.

unbalanced force: Force acting on an object in one direction that is greater/smaller in magnitude than opposing forces.


Pre-Activity Assessment

Pre-Quiz: Have students complete the Assistive Hand Device Pre-Activity Quiz, which has students describe prior knowledge on the structure and function of the human hand, define and describe Newton's three laws of motion as observed in the motions of the human hand and identify the definition of nine forces. Use this as a formal or informal assessment.

Activity Embedded Assessment

Problem Statement: Individually, have students write brief problem statements, given the client's communicated need. Review written answers for information that is essential and ensure that unnecessary details have been excluded from their statements.

Post-Activity Assessment

Worksheet: In design groups, assign students to complete the Reflecting on the Engineering Design Process Worksheet. Review their answers for correct use of vocabulary in written explanations. Also review their answers for the corerct application of physics concepts, as students are asked to describe the forces acting on their prototypes during the final test.

Safety Issues

Instruct students on how to use safely use the tube cutters (or scissors). Observe students while cutting tubes.

Troubleshooting Tips

As students conduct the iterative process of building, testing and redesigning, advise them to consider reusing as many materials as possible. Remind students that they do not get a budget increase for each prototype; they must make do with the overall designated budget.

Activity Extensions

  • Have students apply their knowledge of forces to draw free body diagrams of their prototypes' performances in the final test.
  • Have students explore marketing by assigning criteria for visual appeal. Have students make 1-2 minute commercials. Follow this with a vote by instructors or students from another class.

Activity Scaling

  • For lower grades, do not permit them to use the tube cutter.
  • For higher grades, require design teams to communicate in writing the strengths and weaknesses of their design sketches, before giving out materials. Provide loans with interest, for extra money in the budget.


Kelly Cox, Kristen Billiar, Terri Camesano, Jeanne Hubelbank


© 2015 by Regents of the University of Colorado; original © 2015 Worcester Polytechnic Institute

Supporting Program

Inquiry-Based Bioengineering Research and Design Experiences for Middle-School Teachers RET Program, Department of Biomedical Engineering, Worcester Polytechnic Institute


This activity was developed under National Science Foundation grant no. EEC 1132628. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: March 17, 2019


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