Measurement: Forces

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SWBAT quantify matter by measuring forces on objects using metric units and a spring scale.

Big Idea

Forces happen every time objects interact. Students explore how to measure these invisible pushes and pulls.


20 minutes

Middle school students are pushed and pulled in lots of directions - and they don't like to be forced into anything! Since forces are always acting on objects, students are curious to explore how it is that these invisible things start, stop and change motion. This lesson is not a comprehensive exploration of forces, but rather an introduction to the concept and practice measuring forces using a spring scale.

Understanding forces and how to measure them is fundamental be accessing several NGSS Disciplinary Core Ideas (DCI), especially those related to MS-PS2 Motion and Stability: Forces and Interactions and MS-PS1 Matter and its Interactions. Additionally, as students learn about measurement of forces, they access the Crosscutting Concept related to measurement (standard units are used to measure and describe physical quantities). Also, practice collecting data accurately to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions (SP3) is a scientific practice necessary for planning and carrying out investigations.

This lesson can be used to introduce forces as a stand-alone lesson or in concert with associated lessons. These lessons can be used separately, but the sequence of these related lessons occurs as is follows:

1) Measurement: Mass

2) Measurement: Forces (This lesson)

3) Mass versus Weight: Travel to Other Planets

4) Weighed Down Investigation

5) Other related lessons: Newton's 2nd and 3rd Laws of Motion: Bumper Boats Investigation, Newton's Laws Graffiti  and Newton's Laws of Motion Simulation Investigation.

In order to ENGAGE students in this lesson, give students an index card and ask them to interview at least three other students using this prompt:

What is a force?

Students record the responses from their interviews. Together, generate a class list of ideas on the board. Ask students to evaluate these ideas and vote on/develop one class theory. Watch this video to compare their ideas with ideas about force found on the street. Stop at minute 1:19 and ask:

What are some of the ideas that people on the street suggested that match our theories?

After viewing the video, students suggest revisions to the original theory and continue on to EXPLORE measuring forces.


60 minutes

The EXPLORE stage of the lesson is to get students involved in the topic so that they start to build their own understanding. To help students explore the concept of measuring forces, students use a variety of resources in small groups to complete various activities on the Measurement Force Student Handout. Helpful resources for exploration are here:

1) Science Textbook

2) Virtual Spring Scale

3) Measuring Weight Video

4) Online Scale Measurement Game

As students advance through the EXPLORE stage of the lesson, it is helpful to provide a short direct instruction lesson about how to use a spring scale safely and accurately. This mini-lesson can be conducted table by table or with the whole class. Students need to see and hear the process being modeled or they oftentimes make assumptions about how to use the tool (which results in misuse and inaccurate use).

Once students are shown how to use the spring scale, they practice using the "Mystery Weight Bags". Bags filled with various items are provided and students estimate and measure them to the nearest tenth of a Newton. This is an opportune time to give students additional feedback and instruction about how to use the spring scale

Teacher Note: When creating the Mystery Weight Bags, be sure to secure them in such a way that students can't open them to release the contents but can easily hang them from the spring scale. I use Ziploc bags with red duct tape over the opening with a loop of duct tape. If you want students to find only the weight of the Mystery Bag contents, have them weigh an empty bag with tape to subtract from each of their measurements.


10 minutes

The EXPLAIN stage provides students with an opportunity to communicate what they have learned so far and figure out what it means. During this stage of the lesson, we review the Measurement: Force Student Handout together. I model for students how to neatly complete the activity and we briefly discuss each topic as we review. This stage of the lesson presents a great place for a quick formative assessment because students are able to explain their answers and ask questions about parts of the activity they don't yet understand. When we finish reviewing student work: Measurement Force Student Work, I offer students a clean copy of the notes: Measurement: Force Student Handout Notes.

For an alternate EXPLAIN strategy, this visual activity helps students further explore and explain their conceptual understanding of forces with relation to related concepts of mass, volume and density:


For more on the topic of using mini-lessons as a strategy, read this section's reflection: Borrowing from Language Arts Best Practice: Mini-Lessons within a Workshop Model.


The EXTEND stage allows students to apply new knowledge to a novel situation. For students who move through the activities quickly, I check their work and give them the choice to:

1) Review the concepts by making flashcards, quizzing or reading additional sections from the textbook.

2) Help another student who needs additional support (see Mastery Learning in Science: Students as Teachers).

3) Explore the PhET Force and Motion Simulation or conduct and investigation using this simulation: Newton's Laws of Motion Simulation Investigation.

4) Calculate your weight in Newtons by researching how to calculate weight (force) and finding your mass in pounds on the scale. 


20 minutes

The EVALUATION stage is for both students and teachers to determine how much learning and understanding has taken place. One way to evaluate student learning is by giving students an assessment that focuses on the "remember" and "understand" levels of understanding (Bloom's Revised Taxonomy): Forces and Motion Quiz.

After students show that they have a basic conceptual understanding and can correctly read spring scales, providing students with an opportunity to practice and prove competence in an investigation is an important evaluation method. This additional evaluation gives insight into whether students can "apply" their level of understanding. This is an investigation that works in conjunction with measuring forces: Weighed Down Investigation.