Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 7: Problem 2

What is drag? What causes it? Why do we usually try to minimize it?

Short Answer

Expert verified
Answer: Drag is a force experienced by an object when it moves through a fluid, such as air or water, and acts opposite to the object's direction of motion. It is caused by friction and pressure. Drag is usually minimized to improve efficiency, increase performance, and reduce noise in various systems, such as vehicles, airplanes, and ships. By minimizing drag, energy consumption can be reduced, higher top speeds can be achieved, and noise levels can be lowered.

Step by step solution

01

Introduction to Drag

Drag is a force experienced by an object when it moves through a fluid, such as air or water. It acts opposite to the object's direction of motion, and can be thought of as the fluid resisting the movement of the object.
02

Causes of Drag

Drag is mainly caused due to two reasons: friction and pressure. 1. Friction: Friction occurs at the interface between the object's surface and the fluid due to the viscosity of the fluid, leading to a force called skin friction drag or viscous drag. This force acts parallel to the fluid flow and opposite to the object's motion. 2. Pressure: As an object moves through the fluid, it causes changes in the fluid's velocity and pressure. The pressure drag, sometimes called form drag, occurs when the fluid pressure around the object's leading and trailing edges is different and creates a net force opposing the object's motion.
03

Effects of Drag

The presence of drag affects the efficiency and performance of various systems, such as vehicles, airplanes, and ships. For example, it directly impacts the fuel consumption and top speed of a vehicle. Drag also has an effect on stability and control. As an object moves through a fluid, it loses energy to overcome drag, which reduces its overall performance.
04

Minimizing Drag

We usually try to minimize drag for various reasons: 1. Improve the efficiency: Reducing drag can lead to a significant reduction in energy consumption, especially in vehicles like cars, trains, and planes. The less energy needed to overcome resistance, the more fuel-efficient the vehicle becomes. 2. Increase performance: By minimizing drag, higher top speeds can be achieved since the energy required to overcome drag is smaller. Increases in performance can also lead to improved stability and control. 3. Noise reduction: Drag causes turbulence which in turn creates noise. Reducing drag can help lower the noise level, which is particularly important in applications such as airplanes and cars. In conclusion, drag is a force acting on objects moving through fluids, it is caused by friction and pressure, and we usually try to minimize it to improve efficiency, performance, and noise reduction.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Hot engine oil at \(150^{\circ} \mathrm{C}\) is flowing in parallel over a flat plate at a velocity of \(2 \mathrm{~m} / \mathrm{s}\). Surface temperature of the \(0.5-\mathrm{m}-\) long flat plate is constant at \(50^{\circ} \mathrm{C}\). Determine \((a)\) the local convection heat transfer coefficient at \(0.2 \mathrm{~m}\) from the leading edge and the average convection heat transfer coefficient, and (b) repeat part ( \(a\) ) using the Churchill and Ozoe (1973) relation.

During a plant visit, it was noticed that a 12-m-long section of a \(10-\mathrm{cm}\)-diameter steam pipe is completely exposed to the ambient air. The temperature measurements indicate that the average temperature of the outer surface of the steam pipe is \(75^{\circ} \mathrm{C}\) when the ambient temperature is \(5^{\circ} \mathrm{C}\). There are also light winds in the area at \(10 \mathrm{~km} / \mathrm{h}\). The emissivity of the outer surface of the pipe is \(0.8\), and the average temperature of the surfaces surrounding the pipe, including the sky, is estimated to be \(0^{\circ} \mathrm{C}\). Determine the amount of heat lost from the steam during a 10 -h-long work day. Steam is supplied by a gas-fired steam generator that has an efficiency of 80 percent, and the plant pays \(\$ 1.05 /\) therm of natural gas. If the pipe is insulated and 90 percent of the heat loss is saved, determine the amount of money this facility will save a year as a result of insulating the steam pipes. Assume the plant operates every day of the year for \(10 \mathrm{~h}\). State your assumptions.

Air at \(20^{\circ} \mathrm{C}\) flows over a 4-m-long and 3-m-wide surface of a plate whose temperature is \(80^{\circ} \mathrm{C}\) with a velocity of \(5 \mathrm{~m} / \mathrm{s}\). The rate of heat transfer from the surface is (a) \(7383 \mathrm{~W}\) (b) \(8985 \mathrm{~W}\) (c) \(11,231 \mathrm{~W}\) (d) 14,672 W (e) \(20,402 \mathrm{~W}\) (For air, use \(k=0.02735 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}, \operatorname{Pr}=0.7228, \nu=1.798 \times\) \(\left.10^{-5} \mathrm{~m}^{2} / \mathrm{s}\right)\)

Air \((k=0.028 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}, \operatorname{Pr}=0.7)\) at \(50^{\circ} \mathrm{C}\) flows along a 1 -m-long flat plate whose temperature is maintained at \(20^{\circ} \mathrm{C}\) with a velocity such that the Reynolds number at the end of the plate is 10,000 . The heat transfer per unit width between the plate and air is (a) \(20 \mathrm{~W} / \mathrm{m}\) (b) \(30 \mathrm{~W} / \mathrm{m}\) (c) \(40 \mathrm{~W} / \mathrm{m}\) (d) \(50 \mathrm{~W} / \mathrm{m}\) (e) \(60 \mathrm{~W} / \mathrm{m}\)

Air (1 atm, \(\left.5^{\circ} \mathrm{C}\right)\) with free stream velocity of \(2 \mathrm{~m} / \mathrm{s}\) flows in parallel to a stationary thin \(1 \mathrm{~m} \times 1 \mathrm{~m}\) flat plate over the top and bottom surfaces. The flat plate has a uniform surface temperature of \(35^{\circ} \mathrm{C}\). Determine \((a)\) the average friction coefficient, \((b)\) the average convection heat transfer coefficient, and \((c)\) the average convection heat transfer coefficient using the modified Reynolds analogy and compare with the result obtained in \((b)\).
See all solutions

Recommended explanations on Physics Textbooks

Modern Physics

Read Explanation

Solid State Physics

Read Explanation

Radiation

Read Explanation

Circular Motion and Gravitation

Read Explanation

Famous Physicists

Read Explanation

Thermodynamics

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free