Answer key

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Last edited 26 days ago by Learn LoopHQ.

Chapter: 04. Force

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Contact forces occur when two objects are in direct physical contact and exert force on each other. Examples include muscular force, used when pushing or pulling an object, and the force of friction, which arises when two surfaces rub together. In contrast, non-contact forces act on objects without direct physical touch. Prominent examples are gravitational force, which pulls objects towards each other (like an apple falling from a tree), magnetic force, where magnets attract or repel without touching, and electrostatic force, which acts between charged particles.

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While beneficial, friction also has notable disadvantages. It constantly opposes motion, meaning that more effort or energy is required to move objects or keep them moving. This opposition leads to wear and tear on surfaces, such as shoe soles and vehicle tires wearing out over time. In machines, friction causes wear and tear on moving parts, reducing their lifespan and requiring frequent replacement. Furthermore, friction generates heat, which can reduce the efficiency of machines and lead to energy waste.

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The force of friction is a resistive force that acts between two surfaces in contact, always opposing the relative motion or tendency of motion of one surface over the other. Its strength primarily depends on the nature (roughness or smoothness) of the interacting surfaces; rougher surfaces produce more friction, while smoother surfaces result in less. Additionally, the amount of friction increases with the mass of the object. Its main effect is to try and stop the movement between surfaces.

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Force can initiate motion in an object that is at rest; for instance, pedaling a bicycle exerts force on its pedals, causing it to move. Conversely, force can bring a moving object to a halt; for example, a cricket player applies force with their hands to stop a moving ball. This demonstrates that force is capable of producing motion in stationary objects and stopping objects that are already in motion.

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Friction is crucial for many everyday activities. Firstly, it allows us to walk by providing grip between our feet and the ground, preventing slipping. Secondly, friction enables writing, as it creates resistance between a pencil and paper, allowing ink or graphite to be transferred. Thirdly, vehicles rely on friction between their tires and the road to move and for their brakes to function effectively, bringing them to a stop. Without friction, these fundamental actions would be impossible.

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