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Exploring Forces - What Is a Force?

Grade 8CBSE

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

🔑Concepts

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A force is defined as a push or a pull upon an object resulting from the object's interaction with another object.

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Forces only come into play when at least two objects interact with each other.

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A force has both magnitude (strength) and direction. A change in either magnitude or direction (or both) changes the force.

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The SI unit of force is the Newton, denoted by the symbol NN.

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Forces can change the state of motion of an object: they can move a stationary object, change the speed of a moving object, or change the direction of motion.

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Force can also cause a change in the shape or size of an object (deformation).

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If two forces act on an object in the same direction, the net force is the sum of the two forces: Fnet=F1+F2F_{net} = F_1 + F_2.

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If two forces act in opposite directions on an object, the net force is the difference between the two forces: Fnet=F1−F2F_{net} = F_1 - F_2, acting in the direction of the larger force.

📐Formulae

Fnet=F1+F2 (Forces in the same direction)F_{net} = F_1 + F_2 \text{ (Forces in the same direction)}

Fnet=∣F1−F2∣ (Forces in opposite directions)F_{net} = |F_1 - F_2| \text{ (Forces in opposite directions)}

1 Newton (N)=1 kg⋅m/s21\text{ Newton (N)} = 1\text{ kg} \cdot \text{m/s}^2

💡Examples

Problem 1:

Two brothers are pushing a heavy cabinet in the same direction. Brother A applies a force of 40 N40\text{ N} and Brother B applies a force of 55 N55\text{ N}. Calculate the net force acting on the cabinet.

Solution:

Fnet=40 N+55 N=95 NF_{net} = 40\text{ N} + 55\text{ N} = 95\text{ N} 40+5595\begin{array}{r} 40 \\ + 55 \\ \hline 95 \end{array}

Explanation:

When two forces act in the same direction, their magnitudes are added together to find the resultant or net force.

Problem 2:

In a game of tug-of-war, Team X pulls the rope with a force of 1200 N1200\text{ N} to the left, while Team Y pulls with a force of 1050 N1050\text{ N} to the right. What is the net force and in which direction will the rope move?

Solution:

Fnet=1200 N−1050 N=150 NF_{net} = 1200\text{ N} - 1050\text{ N} = 150\text{ N} 1200−1050150\begin{array}{r} 1200 \\ - 1050 \\ \hline 150 \end{array}

Explanation:

Since the forces are acting in opposite directions, the net force is the difference between them. The rope will move in the direction of the larger force, which is towards the left (Team X).

Problem 3:

If two equal forces of 25 N25\text{ N} act on a block from exactly opposite directions, what is the net force?

Solution:

Fnet=25 N−25 N=0 NF_{net} = 25\text{ N} - 25\text{ N} = 0\text{ N}

Explanation:

When two equal forces act in opposite directions, they cancel each other out, resulting in a net force of zero. The object remains in its current state of motion.