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Balanced and Unbalanced Forces — Reading Comprehension

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MS-PS2-2

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This informational science passage explores the core concepts of balanced and unbalanced forces as aligned with NGSS standards MS-PS2-1 and MS-PS2-2. Students learn how to calculate net force, interpret force diagrams, and understand the cause-and-effect relationships that determine whether an object moves or stays still. Real-world examples, such as a book resting on a table, a tug of war match, and a falling object, help students visualize and apply these ideas. The passage integrates vocabulary, multiple-choice and writing activities, and includes both standard and simplified versions (with Spanish translations), making it accessible for all learners. Force diagrams are described to build scientific thinking and problem-solving skills. Audio integration supports diverse learning needs. This resource is ideal for grades 6-8 and covers key disciplinary core ideas in physical science.

CONTENT PREVIEW

unbalanced-forces-1 — Illustration comparing balanced and unbalanced forces

Forces are pushes or pulls that act on objects, causing them to move, stop, or change direction. The study of balanced and unbalanced forces helps scientists explain why objects behave the way they do in the physical world. Understanding these forces is essential for predicting motion in everything from sports to engineering. The main idea is that the way forces combine determines whether an object stays at rest or moves in a new way.

Net Force: The Sum of All Forces
Every object can have many forces acting on it at once. The net force is the sum of all these forces, including their directions. If two people pull on a rope in opposite directions with equal strength, the net force is zero. Forces are often shown in force diagrams, where arrows represent the size and direction of each force. For example, a book sitting on a table has the downward force of gravity balanced by the upward support force of the table. Since the two forces are equal and opposite, the net force is zero and the book does not move.

Balanced vs. Unbalanced Forces: What Changes?
Balanced forces occur when all the forces on an object cancel each other out, so the net force is zero. In this case, the object stays at rest or continues moving at a constant speed. In contrast, unbalanced forces happen when one force is stronger than the others, so the net force is not zero. This causes the object's motion to change—speeding up, slowing down, or changing direction. In tug of war, if both teams pull equally, the rope stays still (balanced forces). But if one team suddenly pulls harder, unbalanced forces make the rope move in their direction. When an object falls, gravity is an unbalanced force that pulls it toward the ground, causing it to accelerate.

Applications and Broader Implications
Understanding balanced and unbalanced forces is crucial in many areas of science and engineering. Engineers use these principles to design bridges, vehicles, and buildings that remain stable under different loads. Athletes rely on their knowledge of forces to improve their performance, adjusting their movements to create unbalanced forces that help them run faster or jump higher. In the environment, wind and water act as forces that shape landscapes over time. Recognizing how forces interact allows us to solve problems, design safer products, and understand natural events like landslides or storms. These concepts connect to larger scientific ideas about energy, motion, and stability in systems.

In summary, the motion of any object depends on the net force acting upon it. Balanced forces mean no change in motion, while unbalanced forces result in acceleration or deceleration. By analyzing force diagrams and calculating net force, scientists and engineers can predict and control how objects move in our world.

Interesting Fact:
Sir Isaac Newton's laws of motion are the foundation for understanding forces and continue to guide scientific discoveries today.

What is net force?

The sum of all forces acting on an object, including their directionsThe amount of gravity onlyThe force that always moves objects upwardThe difference between mass and weight

What happens when the forces on an object are balanced?

The object changes directionThe object stays at rest or keeps moving at the same speedThe object accelerates quicklyThe object always falls downward

In a tug of war, what causes the rope to move?

Balanced forcesUnbalanced forcesNo forcesGravity only

Which of these is the best definition of 'force diagram' as used in the passage?

A chart for measuring speedA drawing that uses arrows to show forces on an objectA tool for finding massA graph comparing weights

What does 'acceleration' mean in the context of forces?

A change in the speed or direction of motionBeing balancedRemaining stillA measure of weight

Engineers use the concept of balanced and unbalanced forces to:

Design stable bridges and buildingsRun faster in racesDraw picturesGrow plants

If a book is sitting still on a table, what are the two main forces acting on it?

Gravity and the table's upward supportWind and frictionGravity and accelerationMagnetism and electricity