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Exploring Forces - Are Forces an Interaction Between Two Objects?

Grade 8CBSE

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

🔑Concepts

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

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Interaction of one object with another object results in a force between the two objects. At least two objects must be involved for a force to exist.

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Forces applied on an object in the same direction add to one another. The total or net force is the sum of the individual forces.

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If two forces act in opposite directions on an object, the net force is the difference between the two forces. The net force acts in the direction of the larger force.

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The strength of a force is expressed by its magnitude. Force also has a specific direction in which it acts.

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If the magnitude or the direction of a force changes, its effect on the object changes. Forces can change the state of motion (speed/direction) or the shape of an object.

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If two equal forces act on an object in opposite directions, the net force is zero (00).

📐Formulae

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

Fnet=F1−F2 (Forces acting in opposite directions, where F1>F2)F_{net} = F_1 - F_2 \text{ (Forces acting in opposite directions, where } F_1 > F_2 \text{)}

Fnet=0 (When F1=F2 and directions are opposite)F_{net} = 0 \text{ (When } F_1 = F_2 \text{ and directions are opposite)}

💡Examples

Problem 1:

Two students, Amit and Rahul, are pushing a heavy desk in the same direction to move it across the classroom. Amit applies a force of 25 N25\text{ N} and Rahul applies a force of 35 N35\text{ N}. Calculate the net force acting on the desk.

Solution:

Fnet=25 N+35 N=60 NF_{net} = 25\text{ N} + 35\text{ N} = 60\text{ N}

Explanation:

Since both forces are applied in the same direction, the net force is the sum of the individual forces. 25+3560\begin{array}{r} 25 \\ + 35 \\ \hline 60 \end{array}

Problem 2:

In a game of tug-of-war, Team Alpha pulls with a force of 2500 N2500\text{ N} to the left, and Team Beta pulls with a force of 2250 N2250\text{ N} to the right. What is the resultant force and in which direction will the rope move?

Solution:

Fnet=2500 N−2250 N=250 NF_{net} = 2500\text{ N} - 2250\text{ N} = 250\text{ N} towards the left.

Explanation:

When forces act in opposite directions, the net force is the difference between the two. The rope moves in the direction of the greater force. 2500−2250250\begin{array}{r} 2500 \\ - 2250 \\ \hline 250 \end{array}

Problem 3:

A box is being pulled from two opposite sides by two strings. If both strings are pulled with a force of 50 N50\text{ N} each, what is the net force acting on the box?

Solution:

Fnet=50 N−50 N=0 NF_{net} = 50\text{ N} - 50\text{ N} = 0\text{ N}

Explanation:

The two forces are equal in magnitude and opposite in direction. Therefore, they cancel each other out, resulting in a net force of zero. The box remains stationary.