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Zorluk: ZorFriction and Resistance

Match each practical mechanical scenario or design observation to the fundamental principle of friction and resistance that best explains it.

  • Towing a vehicle sideways with locked wheels requires the same lateral force regardless of whether the vehicle is equipped with wide mud tires or narrow street tires, assuming identical total vehicle weight.Kinetic sliding resistance depends on the normal force and material properties, but is generally independent of the macroscopic surface area in contact.
  • Replacing solid bronze journal bearings in a high-speed rotary shaft with steel ball bearings dramatically reduces operating temperatures and mechanical energy loss.Transitioning a system from sliding contact to rotational contact eliminates continuous surface shearing, yielding a substantially lower coefficient of resistance.
  • A heavy crate resting on a steel ramp remains stationary as the incline is slowly raised, until it suddenly breaks loose and accelerates rapidly down the ramp without any additional pushing.Static friction matches applied parallel forces up to a maximum breaking point, after which a typically lower kinetic friction governs the object's motion.
  • A submersible vehicle requires significantly more engine power to increase its cruising speed from 3030 knots to 4040 knots than it does to accelerate from 1010 knots to 2020 knots.Fluid resistance (viscous drag) scales non-linearly with the object's velocity through a medium.

Cevap

The locked wheels scenario pairs with area independence; the bearing replacement pairs with the advantage of rolling resistance over sliding; the accelerating crate pairs with the static friction threshold being overcome by kinetic friction; and the submersible's power demand pairs with the non-linear scaling of fluid drag.
Each scenario perfectly illustrates a unique property of friction: area independence for kinetic sliding, the mechanical advantage of rolling over sliding, the maximum threshold of static resistance transitioning to kinetic, and the velocity-dependent nature of fluid drag.

Adım Adım Çözüm

1
Analyze the tire width scenario.
Identify that changing tire width alters contact area but not vehicle weight or normal force.
The kinetic friction formula (Fk=μkNF_k = \mu_k N) shows that resistance depends strictly on normal force and material coefficient, not surface area.
2
Analyze the bearing replacement scenario.
Recognize the mechanical shift from a journal (sliding) bearing to a ball (rolling) bearing.
Rolling friction coefficients are fundamentally much smaller than sliding kinetic friction coefficients, significantly reducing heat and energy loss.
3
Analyze the sliding crate scenario.
Identify the transition state from stationary to moving.
Static friction resists movement up to a maximum limit (Fs(max)=μsNF_{s(max)} = \mu_s N). Once this is broken, the typically lower kinetic friction takes over, resulting in a sudden net force that causes acceleration.
4
Analyze the submersible speed scenario.
Identify that motion occurs through a fluid medium (water).
Unlike dry kinetic friction which is relatively constant across speeds, fluid drag increases with the square of the velocity, requiring exponentially more power at higher speeds.

Anahtar Kavram

Principles of Static, Kinetic, Rolling, and Fluid Friction
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Konular

Friction and Resistance

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