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Exploring Forces - What Can a Force Do to the Objects on Which It Acts?

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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Force can change the state of motion of an object: It can move a stationary object or change the speed of an object already in motion.

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If the applied force is in the direction of motion, the speed of the object increases. If the force is applied in the direction opposite to the motion, the speed decreases.

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Force can change the direction of motion of a moving object (e.g., a cricketer hitting a ball with a bat).

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Force can change the shape or size of an object (e.g., stretching a rubber band or squeezing a plastic bottle).

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Forces are due to an interaction: At least two objects must interact for a force to come into play.

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Magnitude and Direction: Force is expressed by its magnitude and the direction in which it acts. If the direction or magnitude changes, the effect of the force changes.

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Net Force: When multiple forces act on an object, the total effect is determined by the net force. If two forces act in the same direction, they add up. If they act in opposite directions, the net force is the difference between them.

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

📐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)F_{net} = |F_1 - F_2| \text{ (Forces acting in opposite directions)}

P=FA (Pressure is Force per unit Area)P = \frac{F}{A} \text{ (Pressure is Force per unit Area)}

💡Examples

Problem 1:

Two boys are pushing a heavy box. Boy A applies a force of 25N25 N and Boy B applies a force of 15N15 N in the same direction. What is the net force acting on the box?

Solution:

Fnet=25N+15N=40NF_{net} = 25 N + 15 N = 40 N

Explanation:

When two forces act in the same direction on an object, the net force is the sum of the two forces. Here, 25+15=4025 + 15 = 40. The box will move in the direction of the applied forces.

Problem 2:

In a tug-of-war, Team X pulls with a force of 1200N1200 N to the left, and Team Y pulls with a force of 1050N1050 N to the right. Calculate the net force and determine the direction of movement.

Solution:

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

Explanation:

Since the forces are acting in opposite directions, the net force is the difference between the two. Team X exerts a greater force, so the net force is 150N150 N towards the left (Team X's side).

Problem 3:

What happens to the shape of a lump of dough when you apply force with your hands?

Solution:

The shape of the dough changes.

Explanation:

This is an example of force changing the shape of an object. The force applied by the hands overcomes the internal resistance of the dough, causing a permanent or temporary deformation.

What Can a Force Do to the Objects on Which It Acts? Class 8 Notes & Examples