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Forces and Motion - Balanced and Unbalanced Forces

Grade 6IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A force is a push or a pull acting upon an object as a result of its interaction with another object, measured in Newtons (NN).

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Forces are vector quantities, meaning they have both magnitude (size) and direction.

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The Net Force (FnetF_{net}) is the vector sum of all the individual forces acting on an object.

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Balanced Forces occur when the net force acting on an object is zero (Fnet=0NF_{net} = 0 N). If forces are balanced, an object at rest stays at rest, and an object in motion stays in motion at a constant velocity.

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Unbalanced Forces occur when the net force is not zero (Fnet≠0NF_{net} \neq 0 N). This causes a change in the object's state of motion, leading to acceleration (aa).

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Newton’s First Law (Law of Inertia) states that an object will maintain its state of rest or uniform motion unless acted upon by an unbalanced force.

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Newton’s Second Law relates force, mass, and acceleration, showing that FF is directly proportional to aa for a constant mass (mm).

📐Formulae

Fnet=F1+F2+...+FnF_{net} = F_1 + F_2 + ... + F_n

F=m×aF = m \times a

a=Fnetma = \frac{F_{net}}{m}

💡Examples

Problem 1:

Two students are playing tug-of-war. Student A pulls to the left with a force of 150N150 N. Student B pulls to the right with a force of 200N200 N. Calculate the net force and determine if the forces are balanced or unbalanced.

Solution:

Fnet=200N−150N=50NF_{net} = 200 N - 150 N = 50 N to the right.

Explanation:

Since the forces are acting in opposite directions, we subtract the smaller force from the larger one. Because Fnet>0NF_{net} > 0 N, the forces are unbalanced, and the rope will accelerate to the right.

Problem 2:

A book with a mass of 2kg2 kg sits stationary on a table. The force of gravity pulling it down is 19.6N19.6 N. What is the magnitude of the Normal Force (FNF_N) acting upwards, and are the forces balanced?

Solution:

FN=19.6NF_N = 19.6 N upwards.

Explanation:

Because the book is stationary (not moving), the net force must be zero (Fnet=0NF_{net} = 0 N). Therefore, the upward Normal Force must exactly equal the downward gravitational force to create a state of balanced forces.

Problem 3:

A toy car is pushed with a net force of 10N10 N. If the car has a mass of 0.5kg0.5 kg, calculate its acceleration.

Solution:

a=10N0.5kg=20m/s2a = \frac{10 N}{0.5 kg} = 20 m/s^2

Explanation:

Using Newton's Second Law (F=m×aF = m \times a), we rearrange the formula to solve for acceleration. The unbalanced force causes the car to speed up at a rate of 20m/s220 m/s^2.

Balanced and Unbalanced Forces - Revision Notes & Key Formulas | IB Grade 6 Science