Science · 5th Grade · Engineering Design and Innovation · Weeks 19-27

Forces and Motion

Students will investigate how forces cause changes in an object's motion and direction.

• Common Core State Standards
• 3-PS2-1
• 3-PS2-2

About This Topic

Forces and motion is a cornerstone of NGSS-aligned science for 5th grade students. Students shift from informal ideas about pushing and pulling to a more precise understanding of how forces cause changes in an object's speed, direction, or shape. The key distinction between balanced and unbalanced forces helps students explain why some objects remain still while others accelerate, connecting directly to NGSS performance expectations 3-PS2-1 and 3-PS2-2.

A critical conceptual milestone is learning to predict motion by analyzing the net force on an object. When forces are equal and opposite, the object remains at rest or continues at constant speed; when they are unequal, the object changes its motion. Students practice this through investigations involving friction, a force that often surprises them because it acts opposite to motion without being as visually obvious as a direct push or pull.

Active learning is especially productive here because students can physically experience the concepts. Running friction experiments, building ramps, and using force diagrams in collaborative groups turns an abstract idea into something students can observe, measure, and argue about with evidence.

Key Questions

1. Differentiate between balanced and unbalanced forces.
2. Predict the motion of an object given the forces acting upon it.
3. Design an experiment to demonstrate the effect of friction on an object's movement.

Learning Objectives

• Compare and contrast the effects of balanced and unbalanced forces on an object's motion.
• Predict the change in an object's speed or direction when subjected to a net force.
• Design and conduct an experiment to measure the impact of friction on an object's acceleration.
• Explain how friction opposes motion and affects the distance an object travels.

Before You Start

Introduction to Pushes and Pulls

Why: Students need a basic understanding of pushes and pulls as types of forces before they can analyze more complex force interactions.

Describing Motion

Why: Understanding concepts like speed and direction is necessary to describe how forces change an object's motion.

Key Vocabulary

Force	A push or a pull that can cause an object to move, stop, or change direction.
Balanced Forces	When two or more forces acting on an object are equal in strength and opposite in direction, resulting in no change in motion.
Unbalanced Forces	When forces acting on an object are not equal in strength or not opposite in direction, causing a change in the object's motion (acceleration).
Friction	A force that opposes motion between two surfaces that are in contact, often generating heat.
Acceleration	The rate at which an object's velocity changes over time, meaning it speeds up, slows down, or changes direction.

Watch Out for These Misconceptions

Common Misconception

An object needs a continuous force to keep moving.

What to Teach Instead

Students intuitively believe that motion requires constant force, which is pre-Newtonian thinking. Investigating objects sliding on different surfaces helps them see that friction, not the absence of force, is what stops motion. Peer debates after lab data collection sharpen this correction because students must defend their claims with measured evidence.

Common Misconception

Balanced forces mean nothing is happening.

What to Teach Instead

Students often assume that balanced forces equal zero activity, but a book sitting on a table has two balanced forces acting on it continuously. Collaborative force diagram analysis helps students see that balanced forces describe a stable condition, not an absence of forces.

Common Misconception

Heavier objects always have more force.

What to Teach Instead

Students conflate mass with force. Using spring scales in paired investigations allows students to measure actual forces and see that the force applied depends on the push or pull, not just the object's weight.

Active Learning Ideas

Hands-On Lab: Friction Ramp Investigation

Groups set up a ramp and slide an object over surfaces of varying roughness (sandpaper, smooth plastic, felt). They measure distance traveled across each surface and record data in a shared table, then write a claim-evidence-reasoning statement about friction's effect on motion.

45 min·Small Groups

Think-Pair-Share: Balanced or Unbalanced?

Project images of objects in different motion states (a parked car, a skateboarder speeding up, a tug-of-war rope at rest). Students identify whether forces are balanced or unbalanced, compare reasoning with a partner, then justify their answers to the class.

20 min·Pairs

Role Play: Human Tug-of-War Force Model

Two groups pull on a rope with different numbers of students on each side. The class observes the resulting motion and connects it to net force: more force on one side creates unbalanced forces and motion in that direction. Teacher guides a discussion about what would need to change to make the forces balanced.

15 min·Whole Class

Gallery Walk: Force Diagram Review

Student groups each draw a force diagram for a different scenario (book on a table, rolling ball, bicycle braking) and post them around the room. Classmates tour with sticky notes to mark agreements or corrections, and the class resolves disagreements in a final debrief.

35 min·Small Groups

Real-World Connections

• Engineers designing roller coasters must calculate the forces of gravity, friction, and air resistance to ensure the ride is safe and thrilling for passengers.
• Professional race car drivers use their understanding of friction and unbalanced forces to control their vehicles, making precise turns and accelerating effectively.
• Shipbuilders consider friction when designing hulls, aiming to reduce water resistance to make ships more fuel-efficient as they travel across oceans.

Assessment Ideas

Quick Check

Present students with scenarios: 'A book resting on a table' or 'A soccer ball kicked across grass.' Ask them to identify if the forces are balanced or unbalanced and explain their reasoning in one sentence.

Exit Ticket

Provide students with a diagram showing a box being pushed with two different forces. Ask them to draw an arrow representing the net force and write one sentence predicting how the box will move.

Discussion Prompt

Pose the question: 'Imagine you are pushing a heavy box across a carpet and then across a smooth tile floor. How does friction affect your effort and the box's movement on each surface? What would happen if there were no friction?'

Frequently Asked Questions

How do you teach Newton's laws without using that term in 5th grade?

At this level, NGSS focuses on observable patterns rather than formal laws. Frame everything as cause and effect: what happens to an object when forces are unbalanced? Students develop the same conceptual understanding through investigations and claim-evidence-reasoning, building a foundation for naming the laws formally in middle school.

What real-world examples work best for demonstrating friction?

Sports examples connect strongly with students: sliding on a gym floor vs. grass, a bicycle braking, or a shoe on ice. Local examples tied to school experiences, like hallways or playgrounds, make friction immediately relevant. Friction also opens a natural engineering connection: why do tires have tread?

How do you help students understand balanced vs. unbalanced forces?

Tug-of-war activities and force diagrams are highly effective. Using simple arrows to represent forces, students can see when forces cancel out and when they do not. Having students draw and critique each other's diagrams in a gallery walk makes the abstract visual and social.

What active learning strategies work best for teaching forces and motion?

Inquiry-based investigations where students predict outcomes before measuring create productive cognitive conflict when results surprise them. Explaining data to another group through a structured share-out cements the concept far better than direct instruction alone, because students must translate their observations into precise language.