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A centrifuge is a device in which a small container of material is rotated at a high speed on a circular path. Such a device is used in medical laboratories, for instance, to cause the more dense red blood cells to settle through the less dense blood serum and collect at the bottom of the container. Suppose the centripetal acceleration of the sample is \(6.25 \times 10^{3}\) times as large as the acceleration due to gravity. How many revolutions per minute is the sample making, if it is located at a radius of \(5.00 \mathrm{cm}\) from the axis of rotation?

Short Answer

Expert verified
The sample makes approximately 10580 revolutions per minute.

Step by step solution

01

Understanding the Given Values

We are given the centripetal acceleration (\(a_c\)) as \(6.25 \times 10^{3}\) times the acceleration due to gravity (\(g\)). The radius \(r\) is also given as \(5.00\, \text{cm}\), which is equal to \(0.05\, \text{m}\). We need to find the number of revolutions per minute (RPM).
02

Calculating Centripetal Acceleration

Centripetal acceleration \(a_c\) can be expressed as \(a_c = 6.25 \times 10^{3} \times g\). Given \(g = 9.81\, \text{m/s}^2\), the centripetal acceleration is calculated as:\[a_c = 6.25 \times 10^{3} \times 9.81 = 61312.5\, \text{m/s}^2\]
03

Centripetal Acceleration Formula

The formula for centripetal acceleration is \(a_c = \omega^2 r\), where \(\omega\) is the angular velocity in radians per second. We need to solve for \(\omega\):\[\omega^2 = \frac{a_c}{r} = \frac{61312.5}{0.05}\]
04

Calculating Angular Velocity (Omega)

Substitute the values into the equation from Step 3:\[\omega^2 = \frac{61312.5}{0.05} = 1226250\]\[\omega = \sqrt{1226250} \approx 1107.35\, \text{rad/s}\]
05

Converting Angular Velocity to Revolutions per Minute (RPM)

The relationship between angular velocity in rad/sec and RPM is \(1 \text{ rad/sec} = \frac{60}{2\pi} \text{ RPM}\). So:\[\text{RPM} = 1107.35 \times \frac{60}{2\pi} \approx 10579.73\]Therefore, the sample makes approximately 10580 revolutions per minute.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Centripetal Acceleration
Centripetal acceleration is a crucial concept when it comes to understanding circular motion. It refers to the acceleration experienced by an object moving in a circular path, directed toward the center of the circle. This force is necessary to keep the object moving along the curved path instead of flying off tangentially due to inertia. You can think of it as the "center-seeking" force.

The formula to calculate centripetal acceleration is \(a_c = \omega^2 r\), where \(\omega\) is the angular velocity in radians per second and \(r\) is the radius of the circular path. In our example, this formula helps us determine how fast the centrifuge spins to achieve an acceleration that is 6250 times the acceleration due to gravity \(g\).

Understanding centripetal acceleration is pivotal in applications ranging from roller coasters to washing machines, and especially in medical lab centrifuges where separating materials based on density is key.
Angular Velocity
Angular velocity is a measure of how fast an object rotates or spins around a central point. It's typically expressed in radians per second (rad/s), offering a standardized way to talk about rotational speed.

In our centrifuge problem, we found the angular velocity by calculating \(\omega = \sqrt{\frac{a_c}{r}}\), where \(a_c\) is the given centripetal acceleration and \(r\) is the radius. An angular velocity of approximately 1107.35 rad/s tells us how quickly the test sample spins inside the centrifuge.

In everyday terms, if you've ever watched a spinning wheel, the angular velocity is like how fast that wheel turns around its center. High angular velocities mean faster rotations, which is exactly what’s necessary in lab centrifuges to separate components effectively.
Revolutions per Minute (RPM)
Revolutions per minute (RPM) is a more intuitive unit for measuring rotational speed, particularly when thinking about devices that spin, like car engines or fans. It describes how many complete turns an object makes in one minute.

In scientific calculations, we often convert angular velocity from radians per second to RPM because it’s easier for people to visualize and understand in practical terms. The conversion is done using the relationship: \(\text{RPM} = \omega \times \frac{60}{2\pi}\). In our case, converting 1107.35 rad/s gives us approximately 10,580 RPM.

This final number signifies just how rapidly the centrifuge spins, effectively illustrating the powerful forces at work in separating materials within the device. RPM offers an accessible way to grasp the speed in context of real-world applications.

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Most popular questions from this chapter

The following table lists data for the speed and radius of three examples of uniform circular motion. Find the magnitude of the centripetal acceleration for each example. $$ \begin{array}{lcc} & \text { Radius } & \text { Speed } \\ \hline \text { Example 1 } & 0.50 \mathrm{m} & 12 \mathrm{m} / \mathrm{s} \\ \hline \text { Example 2 } & \text { Infinitely large } & 35 \mathrm{m} / \mathrm{s} \\ \hline \text { Example 3 } & 1.8 \mathrm{m} & 2.3 \mathrm{m} / \mathrm{s} \\ \hline \end{array} $$

A child is twirling a \(0.0120-\mathrm{kg}\) plastic ball on a string in a horizontal circle whose radius is \(0.100 \mathrm{m}\). The ball travels once around the circle in 0.500 s. (a) Determine the centripetal force acting on the ball. (b) If the speed is doubled, does the centripetal force double? If not, by what factor does the centripetal force increase?

\(\mathrm{A}\) satellite has a mass of \(5850 \mathrm{kg}\) and is in a circular orbit \(4.1 \times\) \(10^{5} \mathrm{m}\) above the surface of a planet. The period of the orbit is \(2.00 \mathrm{hours}\). The radius of the planet is \(4.15 \times 10^{6} \mathrm{m} .\) What would be the true weight of the satellite if it were at rest on the planet's surface?

A satellite is in a circular orbit about the earth \(\left(M_{\mathrm{E}}=5.98 \times \mathrm{x}\right.\) \(10^{24} \mathrm{kg}\) ). The period of the satellite is \(1.20 \times 10^{4} \mathrm{s} .\) What is the speed at which the satellite travels?

The National Aeronautics and Space Administration (NASA) studies the physiological effects of large accelerations on astronauts. Some of these studies use a machine known as a centrifuge. This machine consists of a long arm, to one end of which is altached a chamber in which the astronaut sits. The other end of the arm is connected to an axis about which the arm and chamber can be rotated. The astronaut moves on a circular path, much like a model airplane flying in a circle on a guideline. The chamber is located \(15 \mathrm{m}\) from the center of the circle. At what speed must the chamber move so that an astronaut is subjected to 7.5 times the acceleration due to gravity?

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