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The Great Tug-of-War Balanced Forces

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Lesson Plan

The Great Tug-of-War: Balanced Forces

Students will use a model to illustrate that balanced forces acting on an object result in no change in its motion (the object remains at rest or moves at a constant speed).

Understanding balanced forces helps us explain why objects stay put or move steadily, connecting directly to how things work in our everyday world.

Audience

7th Grade Students

Time

45 minutes

Approach

Through interactive simulation, discussion, and diagramming.

Materials

The Balancing Act Slide Deck, Virtual Tug-of-War Game, and Balanced Forces Diagramming Worksheet

Prep

Teacher Preparation

15 minutes

Step 1

Warm-Up: Reviewing Net Force (5 minutes)

5 minutes

  • Begin with a quick review of 'net force' from the previous lesson using the first slide of The Balancing Act Slide Deck.
    * Ask students to share what they remember about how forces combine.
    * Introduce the lesson's objective: understanding balanced forces.

Step 2

Activity: Tug-of-War Simulation (15 minutes)

15 minutes

  • Direct students to the Virtual Tug-of-War Game.
    * Instruct them to experiment with different force combinations to achieve a 'balanced' state (where the rope doesn't move or moves at a constant speed).
    * Encourage discussion in small groups about their observations: What happens when forces are equal and opposite? What does 'no change in motion' look like?

Step 3

Discussion & Explanation: Diagramming Balanced Forces (15 minutes)

15 minutes

  • Use The Balancing Act Slide Deck to explain the concept of balanced forces, net force of zero, and equilibrium.
    * Distribute the Balanced Forces Diagramming Worksheet.
    * Guide students through the first example on the worksheet, demonstrating how to draw force arrows and calculate net force.
    * Circulate and provide support as students complete the remaining problems.

Step 4

Cool-Down: Real-World Scenarios (10 minutes)

10 minutes

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Slide Deck

The Great Tug-of-War: Balanced Forces

What happens when forces are equal?

Let's find out!

Greet students and start with a fun, engaging question to grab their attention. Briefly explain that today's lesson will explore what happens when forces are 'balanced.'

Review: What is Net Force?

Remember our friend, Net Force?

  • Net Force: The overall force acting on an object.
  • It's the sum of all individual forces.
  • Can it be zero? What does that mean?

Review the concept of net force from the previous lesson. Ask students to define it and provide examples. Emphasize that net force is the total force acting on an object.

Balanced Forces: The Fair Fight!

When forces are balanced...

  • They are equal in magnitude.
  • They are opposite in direction.
  • The net force is ZERO!

Introduce balanced forces. Explain that when forces are balanced, the net force is zero. Use the tug-of-war analogy to make it relatable.

What Does a Net Force of Zero Mean for Motion?

If the net force is zero, an object will:

  1. Stay at rest (if it's already still).
  2. Continue moving at a constant speed in a straight line (if it's already moving).

This is called equilibrium!

Explain the two scenarios for balanced forces: objects at rest and objects moving at a constant speed (equilibrium). Provide clear, simple examples for each.

Time to Play! Virtual Tug-of-War!

Let's test our understanding!

  • Go to the Virtual Tug-of-War Game link.
  • Experiment with different forces.
  • Try to make the forces balanced! What do you observe?

Explain the upcoming activity. Ensure students understand they need to find ways to balance the forces in the simulation. Encourage them to observe closely what happens to the 'rope' in balanced situations.

Diagramming Balanced Forces

How do we show balanced forces?

  • We use force diagrams!
  • Draw arrows to show:
    • Direction (which way the force is pulling/pushing)
    • Magnitude (how strong the force is - longer arrow = stronger force)

Introduce the worksheet and explain how to draw force diagrams. Emphasize drawing arrows to represent magnitude and direction. Walk through an example together.

Balanced Forces in Our World

Where do we see balanced forces every day?

  • A book sitting on a table.
  • A car cruising down the highway at a steady speed.
  • A planet orbiting the sun (this one's tricky!).

Discuss: What makes these balanced?

Lead a discussion on the real-world examples. Ask students to explain why they think a particular scenario involves balanced forces.

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Game

Virtual Tug-of-War: Find the Balance!

Objective

Your mission is to make the forces on both sides of the rope perfectly balanced, so the rope doesn't move or moves at a constant speed!

How to Play

  1. Imagine your team: You have two teams, Team A and Team B, pulling on a rope.
  2. Assign Force Values: Each person on a team pulls with a certain amount of force (e.g., 10 Newtons).
  3. Scenario 1: Starting at Rest
    • Team A has 3 players pulling to the left.
    • Team B has 2 players pulling to the right.
    • Your Task: Add or remove players from Team B to make the net force zero. What happens to the rope?






  4. Scenario 2: Moving at a Constant Speed
    • Team A has 5 players pulling to the left.
    • Team B has 5 players pulling to the right.
    • Your Task: If the rope is already moving to the left at a constant speed, and the teams are pulling with equal force, what can you say about the forces? What happens if Team B suddenly adds a player?






  5. Scenario 3: Design Your Own!
    • Create your own scenario where forces are unbalanced, and then describe how you would balance them.
    • Explain what happens to the motion of the rope in both the unbalanced and balanced situations.











Reflect and Discuss

  • What did you notice when the forces were balanced? How did the rope move (or not move)?
  • What strategies did you use to achieve balanced forces?
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Worksheet

Balanced Forces Diagramming Worksheet

Instructions

For each scenario below, draw a force diagram using arrows to represent the forces acting on the object. Make sure the length of your arrows represents the magnitude (strength) of the force, and the direction of your arrows represents the direction of the force. Then, calculate the net force and describe the resulting motion of the object.

Problem 1

A book is resting on a table. Gravity pulls the book down with 10 N of force. The table pushes the book up with 10 N of force.

  • Draw your force diagram here:





  • Net Force:


  • Resulting Motion:


Problem 2

Two students are playing tug-of-war. John pulls the rope to the left with 75 N of force. Emily pulls the rope to the right with 75 N of force.

  • Draw your force diagram here:





  • Net Force:


  • Resulting Motion:


Problem 3

A car is cruising down a straight highway at a constant speed. The engine provides 500 N of forward thrust. Air resistance and friction combine to create 500 N of backward drag.

  • Draw your force diagram here:





  • Net Force:


  • Resulting Motion:


Problem 4

An elevator is stopped on the 5th floor. The elevator cable pulls up with 8000 N of force. The weight of the elevator (and its passengers) pulls down with 8000 N of force.

  • Draw your force diagram here:





  • Net Force:


  • Resulting Motion:


Problem 5 (Challenge!)

A pendulum is at the lowest point of its swing, momentarily moving at a constant speed (before it starts to slow down). Gravity pulls down, and the string pulls up and slightly inward. How could these forces be considered balanced at that instant for constant speed?

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