Question 1

Fluids have viscosity because

Accepted Answer

Viscosity in fluids arises due to the interactions between the atoms and molecules within the fluid, which produce internal frictional forces. These interactions can be due to various forces such as van der Waals forces, dipole-dipole interactions, or hydrogen bonding, depending on the nature of the fluid. This internal friction opposes the motion of the fluid layers relative to each other, leading to the characteristic resistance to flow that defines viscosity.

Question 2

When a fluid is in steady - state flow and its path bends, the pressure on the outside of the bend is always

Accepted Answer

When a fluid in steady-state flow encounters a bend, the pressure on the outside of the bend increases due to the centripetal force required to change the direction of the fluid particles. This results in a pressure gradient across the bend, with the pressure being higher on the outside than on the inside.

Question 3

Honey is about _______ times more viscous than air.

Accepted Answer

Honey is approximately 1,000,000 times more viscous than air, reflecting its thick, slow-flowing nature compared to the ease with which air moves.

Question 4

One of the many things that make an artery blockage dangerous is

Accepted Answer

The amount of fluid passing through a blockage in an artery (or any tube) is proportional to the fourth power of the diameter of the opening, according to the Hagen-Poiseuille equation. This means that even a small decrease in the diameter due to blockage can lead to a significant reduction in blood flow.

Question 5

The pressure in a water pipe may not necessarily be lower in regions where the water moves faster when

Accepted Answer

In a non-level pipe, gravitational potential energy differences can affect pressure, potentially overriding the effects of fluid velocity on pressure.

Question 6

You are out watering the lawn and your neighbor decides to strike up a conversation with you. She says that she bought an extra long hose because of all the factors that affect how much water travels through a hose, the length is clearly not one of them because the water is incompressible so what goes in equals what comes out. Please comment on the scientific accuracy of her statement.

Accepted Answer

The answer of You are out watering the lawn and...

Question 7

The four things that affect the amount of water flowing through a hose are

Accepted Answer

The amount of water flowing through a hose is affected by water viscosity (which impacts the flow rate due to internal friction), hose length (longer hoses have more resistance to flow), inlet and outlet pressures (differential pressure drives the flow), and hose diameter (larger diameters allow for more flow). These factors collectively influence the hydraulic conditions within the hose, determining the flow rate and efficiency.

Question 8

Tennis ball A is dry and fuzzy. Tennis ball B is wet, and the fuzz is matted down. What will happen when the two balls are hit horizontally so as to have the same initial horizontal velocity?

Accepted Answer

The fuzz on tennis ball A reduces drag, allowing it to travel farther than tennis ball B.

Question 9

You are at the park throwing a stick for your dog to fetch. When you throw a smooth straight stick by one end, it tends to tumble end over end as it flies through the air. However, when you throw a stick that still has some leaves attached to one end, it flies through the air without tumbling and travels in a smooth arc with the stick leading and the leaves trailing. This automatic alignment occurs because

Accepted Answer

The answer of You are at the park throwing a...

Question 10

On a windy day you notice that a tall light pole is bent away from its equilibrium position. If the wind speed were to increase the pole would

Accepted Answer

Aerodynamic drag forces increase with the speed of the air moving around an object, so if the wind speed increases, the force bending the pole will also increase, causing the pole to bend further from its equilibrium position.

Question 11

Why does fuzz on a tennis ball help it travel farther when hit?

Accepted Answer

The fuzz on a tennis ball "trips" the boundary layer of air around the ball into a turbulent state. This turbulence reduces the size of the wake behind the ball, which in turn reduces drag, allowing the ball to travel farther.

Question 12

Suppose that we are able to send astronauts to Mars and they engage in a game of golf on the red planet's surface. Given that the atmosphere on Mars is considerably less dense than our own, how will the path of the ball be affected?

Accepted Answer

The less dense atmosphere on Mars means there is less air resistance (drag) acting on the golf ball, allowing it to travel further. Additionally, Mars has lower gravity than Earth, which also contributes to the ball traveling further than it would on Earth.

Question 13

Dimples on a golf ball hit without spin

Accepted Answer

Dimples on a golf ball create a turbulent layer of air around the ball which reduces drag by allowing the air to flow more smoothly over the ball's surface, compared to a smooth ball which experiences more drag due to a larger wake.

Question 14

If a golf ball were smooth rather than dimpled, it would

Accepted Answer

The dimples on a golf ball create turbulence in the layer of air next to the ball, which reduces drag and allows the ball to fly farther than it would if it were smooth. A smooth ball experiences more air resistance and does not travel as far.

Question 15

A curve ball in baseball curves because of

Accepted Answer

Curve balls in baseball curve primarily due to lift forces, which are a result of the Magnus effect. This effect occurs when the spinning ball creates a differential in air pressure on either side of the ball, causing it to move in the direction of the lower pressure side.

Question 16

You have two golf balls that differ only in their surfaces. One has dimples, while the other is smooth. Which ball has a greater pressure difference between the leading and trailing edges?

Accepted Answer

The smooth golf ball experiences a greater pressure difference between the leading and trailing edges compared to the dimpled ball. The dimples on a golf ball create turbulence in the air around the ball, which reduces the separation of the flow of air from the ball's surface. This reduction in separation decreases the wake (the area of low pressure behind the ball) and thus reduces the pressure difference between the front and back of the ball. The smooth ball, without these dimples, has a larger wake and a greater pressure difference, leading to more drag.

Question 17

Suppose you have gotten a new job where you have to design balls that fly through the air with as little resistance as possible. You know that in front of the ball there is laminar flow, so in back of the ball there should be

Accepted Answer

Laminar flow is a type of fluid flow in which the fluid flows in parallel layers, with no disruption between the layers. In the case of a ball flying through the air, laminar flow is desired in front of the ball because it creates less drag. In back of the ball, laminar flow is also desired because it helps to create a vacuum that pulls the ball forward.

Question 18

A curve ball's path bends to the right as it flies toward home plate because it is experiencing an aerodynamic force to its right. One reason why the ball is experiencing this aerodynamic force is that the ball is spinning and that spin

Accepted Answer

The spin of the ball causes the air to flow more rapidly around the right side of the ball than around the left side, creating a pressure difference that results in an aerodynamic force to the right.

Question 19

Suppose you are practicing baseball and throw the ball with a spin so that it moves forward and curves to the right. Now when the actual game takes place you are pitching with the wind behind you. Please explain how you could alter your throw so as to make the ball take the same path.

Accepted Answer

The answer of Suppose you are practicing baseball and throw...

Question 20

Suppose you are practicing baseball and throw the ball with a spin so that it moves forward and curves to the right. Now when the actual game takes place you are pitching into the wind. Please explain how you could alter your throw so as to make the ball take the same path.

Accepted Answer