Concept explainers
Sticky Liquids BIO
The drag force on an object moving in a liquid is quite different from that in air. Drag forces in air are largely the result of the object having to push the air out of its way as it moves. For an object moving slowly through a liquid, however, the drag force is mostly due to the viscosity of the liquid, a measure of how much resistance to flow the fluid has. Honey, which drizzles slowly out of its container, has a much higher viscosity than water, which flow's fairly freely.
The viscous drag force in a liquid depends on the shape of the object, but there is a simple result called Stokes’s law for the drag on a sphere. The drag force on a sphere of radius r moving at speed v through a fluid with viscosity η is
At small scales, viscous drag becomes very important To a paramecium (figure 1.2), a single-celled animal that can propel itself through water with fine hairs on its body, swimming through water feels like swimming through honey would to you. We can model a paramecium as a sphere of diameter
Figure 1.2
If the paramecium doubles its swimming speed, how does this change the drag force?
A. The drag force decreases by a factor of 2.
B. The drag force is unaffected.
C. The drag force increases by a factor of 2.
D. The drag force increases by a factor of 4.
Want to see the full answer?
Check out a sample textbook solutionChapter P Solutions
College Physics: A Strategic Approach (4th Edition)
Additional Science Textbook Solutions
Sears And Zemansky's University Physics With Modern Physics
Physics: Principles with Applications
The Cosmic Perspective (8th Edition)
University Physics (14th Edition)
College Physics (10th Edition)
Physics (5th Edition)
- (a) When rebuilding her car's engine, a physics major must exert 300 N of force to insert a dry steel piston into a steel cylinder. What is the magnitude of the normal force between the piston and cylinder? (b) What is the magnitude of the force would she have to exert if the steel parts were oiled?arrow_forwardYou are part of a team in an engineering class that is working on a scale model of a new design for a life vest. You have been asked to find the mass of a piece of foam that will be used for flotation. Because the piece is too bulky to fit on your balance, you break it into two parts. You measure the mass of the first part as 128.3 0.3 g and the second part as 77.0 0.3 g. a. What are the maximum and minimum values for the total mass you might reasonably report? b. What is the best estimate for the total mass of the foam? Hint: Propagation of uncertainty is described in Appendix A.arrow_forwardIn many textbook problems, we ignore certain complications such as friction and drag. The problems contain key words that indicate such a simplification is being used. For example, if a surface is described as slippery, it means that we can ignore friction. Look at the previous chapters problem sets. Find five uses of these key words and explain how to interpret each case.arrow_forward
- On October 21, 2001, Ian Ashpole of the United Kingdom achieved a record altitude of 3.35 km (11 000 ft) powered by 600 toy balloons filled with helium. Each filled balloon had a radius of about 0.50 m and an estimated mass of 0.30 kg. (a) Estimate the total buoyant force on the 600 balloons. (b) Estimate the net upward force on all 600 balloons, (c) Ashpole parachuted to Earth after the balloons began to burst at the high altitude and the system lost buoyancy. Why did the balloons burst?arrow_forwardCasting molten metal is important in many industrial processes. Centrifugal casting is used for manufacturing pipes, bearings, and many other structures. A variety of sophisticated techniques have been invented, but the basic idea is as illustrated in Figure P4.35. A cylindrical enclosure is rotated rapidly and steadily about a horizontal axis. Molten metal is poured into the rotating cylinder and then cooled, forming the finished product. Turning the cylinder at a high rotation rate forces the solidifying metal strongly to the outside. Any bubbles are displaced toward the axis, so unwanted voids will not be present in the casting. Sometimes it is desirable to form a composite casting, such as for a bearing. Here a strong steel outer surface is poured and then inside it a lining of special low-friction metal. In some applications, a very strong metal is given a coating of corrosion-resistant metal. Centrifugal casting results in strong bonding between the layers. Suppose a copper sleeve of inner radius 2.10 cm and outer radius 2.20 cm is to be cast. To eliminate bubbles and give high structural integrity, the centripetal acceleration of each bit of metal should be at least 100g. What rate of rotation is required? State the answer in revolutions per minute.arrow_forwardElisha Graves Otis invented the elevator brake in the mid-1800s, making it possible to build tall skyscrapers with fast elevators. Todays skyscrapers are a large fraction of a mile tall; for example. Taipei 101 in Taiwan has 101 stories and is 515 m (0.32 miles) tall. The top speed of the elevator in the Taipei 101 tower is roughly three times greater than the ascent rate of a commercial jet airplane. The position and time data in the table are based on such an elevator. a. Working in SI units, make a position-versus-time graph for the elevator. (You may wish to use a spreadsheet program.) b. Describe the motion of the elevator in words. c. Find the highest speed of the elevator. When is the elevator going at this speed? d. What sort of considerations would the engineers need to make to ensure the comfort of the passengers?arrow_forward
- Review. A rifle bullet with a mass of 12.0 g traveling toward the right at 260 m/s strikes a large hag of sand and penetrates it to a depth of 23.0 cm. Determine the magnitude and direction of the friction force (assumed constant) that acts on the bullet.arrow_forwardA skydiver will reach a terminal velocity when the air drag equals their weight. For a skydiver with high speed and a large body, turbulence is a factor. The drag force then is approximately proportional to the square of the velocity. Taking the drag force to be FD=12Av2 and setting this equal to the person's weight, find the terminal speed for a person falling "spread eagle." Find both a formula and a number for vt, with assumptions as to size.arrow_forwardAn athlete grips a light rope that passes over a low-friction pulley attached to tire ceiling of a gym. A sack of sand precisely equal in weight to the athlete is tied to the other end of the rope. Both the sand and the athlete are initially at rest. The athlete climbs the rope, sometimes speeding up and slowing down as he does so. What happens to the sack of sand? Explain.arrow_forward
- Consider a child holding a helium balloon in a closed car at rest. What would the child observe the balloon to do when the car (a) accelerates from rest and (b) brakes to a stop? (The balloon does not touch the roof of the car.)arrow_forwardQUESTION 6 Consider a system where a bunch of balloons are attached to a block by a string that rests on a frictionless surface. The balloons that have a mass of m2=50 grams exerts a buoyancy force of Fh = 10N on the block of mass m1 = 5 kg. The string and pulley are massless. a) draw the freebody diagrams for the two masses in the system. b) Sum the forces for block 1. c) Sum the forces for the balloon. m2 d) What is the acceleration of the block? m1arrow_forwardQ2/What is the purpose of having the negative sign in? Hooke's Lawarrow_forward
- Physics for Scientists and Engineers: Foundations...PhysicsISBN:9781133939146Author:Katz, Debora M.Publisher:Cengage LearningPhysics for Scientists and Engineers, Technology ...PhysicsISBN:9781305116399Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781938168000Author:Paul Peter Urone, Roger HinrichsPublisher:OpenStax College
- College PhysicsPhysicsISBN:9781305952300Author:Raymond A. Serway, Chris VuillePublisher:Cengage LearningGlencoe Physics: Principles and Problems, Student...PhysicsISBN:9780078807213Author:Paul W. ZitzewitzPublisher:Glencoe/McGraw-HillAn Introduction to Physical SciencePhysicsISBN:9781305079137Author:James Shipman, Jerry D. Wilson, Charles A. Higgins, Omar TorresPublisher:Cengage Learning