In this hands-on STEM investigation, students will explore net force, balanced forces, and unbalanced forces by analyzing force interactions in the horizontal direction. Using force diagrams and simple calculations, students learn how multiple forces act on an object and how to determine whether those forces cancel out or cause motion.

Students model forces using free-body diagrams, calculate net force with direction, and decide whether forces are balanced (net force = 0 N) or unbalanced (net force ≠ 0 N). Through repeated trials, data collection, and a structured Claim–Evidence–Reasoning (CER) response, students connect force calculations to real-world motion in a clear, visual way.

This investigation can be run as a hands-on lab using spring scales and a cart, or as a no-equipment paper-based investigation using included force-diagram task cards—making it flexible for any classroom.

Learning Targets

• Plan and carry out a controlled investigation with repeated trials
• Represent forces using force arrows and free-body diagrams
• Calculate net force in the horizontal direction
• Determine whether forces are balanced or unbalanced
• Use evidence to explain how net force affects motion

What’s Included

Teacher Guide

Background explanations of net force, balanced vs unbalanced forces, setup guidance, classroom management tips, and common student misconceptions with fixes. Includes implementation notes for both hands-on and paper-based versions.

Student Packet

Hypothesis prompt, variables chart, step-by-step investigation instructions, force-diagram practice, 5-trial data table, analysis questions, and a guided CER response.

Analysis & Answer Key

Sample calculations, expected patterns, completed data examples, detailed reasoning explanations, CER model responses, and common error notes.

Rubric

Assesses experimental design, force diagrams, net force calculations, balanced vs unbalanced reasoning, CER quality, collaboration, and safety.

What Students Will Learn

• How multiple forces act on an object at the same time
• How to calculate net force using magnitude and direction
• The difference between balanced and unbalanced forces
• How force diagrams represent real-world interactions
• How net force determines changes in motion
• How to support explanations using evidence and reasoning
  

Why Teachers Love It

• Flexible setup — works with or without equipment
• Clear visuals make abstract force concepts easier to understand
• Builds core physics skills: diagrams, calculations, and reasoning
• Includes structured CER writing for deeper understanding
• Low prep and easy to manage
• Perfect for forces units, review lessons, stations, or sub plans

➡️ You can get this STEM as well as all my other ones in this series inside my STEM Investigations Growing Bundle. As more labs are added, the price will increase. CLICK HERE to have a look

Best For

Physical Science (forces & motion), physics foundations, lab skills, force diagrams, CER writing, STEM investigations, or sub-friendly lessons.

Materials Needed

Option A (Hands-On):
Small cart or toy car (or smooth box), 2 spring scales (Newton meters), string, masking tape

Option B (No Equipment):
Printed force-diagram task cards (included), calculator

Estimated Timing

1 class period for setup → investigation → data collection → CER writing
Optional extension for discussion or additional task cards

➡️ You can get this activity inside my STEM Investigations Growing Bundle.

I also have the following STEM Labs in My Store:

• Blow Cup Challenge STEM Lab
• Paper Table STEM Lab
• Pendulum STEM Lab
• Parachute STEM Lab
• Catapult STEM Lab
• Paper Airplane - Angle of Attack STEM Lab
• Bottle Flip STEM Lab
• Paper Helicopter STEM Lab
• Yeast Balloon STEM Lab
• Balloon Lift Design STEM Lab
• Candy Combustion Calorimetry STEM Lab
• Marble Ramp: Height vs Average Speed STEM Lab
• Clean Water Filtration STEM Lab
• Beetle Genetics STEM Lab
• Adaptations by Design - Extreme Environments STEM Lab
• Newton's 1st Law of Motion STEM Lab - Penny and Index Card - Inertia Test
• Newton's 2nd Law of Motion STEM Lab - Balloon Rocket
• Newton's 3rd Law of Motion STEM Investigation - Thrust vs Nozzle Size
• Electromagnet - Coil Turns vs Magnetic Strength
• Oobleck: Force vs Flow — Non-Newtonian Fluids
• Homemade Lava Lamp - Density & Gas Production - STEM Investigation
• Net Force - Balanced vs Unbalanced Forces - STEM Investigation

NGSS alignment

MS-PS2-1, MS-PS2-2 (Forces & Motion)

Practices: Planning & Carrying Out Investigations; Using Mathematics & Computation; Analyzing Data; Constructing Explanations; Argument from Evidence

Assessment

Use the included rubric to score experimental design, procedure consistency, observation quality, scientific reasoning, CER strength, collaboration, and safety.