\text {Circumference} = 39,350 \text {\ kilometers} Circumference = 39,350 kilometers. = {\displaystyle e} Compute the circumference of the Earth using the distance and angle measurements you have. The radius is more like 6,371 kilometers at the north and south poles. Historically, these models were based on regional topography, giving the best reference ellipsoid for the area under survey. Although the precise strength of Earth's gravity varies depending on location, the nominal "average" value at the Earth's surface, known as standard gravity is, by definition, 9.80665 m/s 2 (32.1737 ft/s 2 ). As such, they are topographical geocentric distances, Rt, which depends not only on latitude. The cookie is used to store the user consent for the cookies in the category "Performance". You have to use the distance from the center of the Earth, not the distance above Earth's surface, as the radius. , and because Have your partner do the same in her location. Its nice to determine that measurements taken by a lot of groups, sometimes in under ideal conditions, came so near to the right answer. What is the radius of the earth? r This requires an elliptic integral to find, given the polar and equatorial radii: The rectifying radius is equivalent to the meridional mean, which is defined as the average value of M:[14]. What is radius of Earth in gravitation Class 9? Circumference of Earth is the length or the distance around the Earth. Exponential or Scientific Notation: It is easier to write very large numbers such as 100,000,000 as 10 8 (1 followed by 8 0s). How did early mathematicians determine the radius of the earth? The Earth's meridional radius of curvature at the equator equals the meridian's semi-latus rectum: The Earth's prime-vertical radius of curvature at the equator equals the equatorial radius, N = a. (C = 2r) With this information, Eratosthenes inferred that the Earths radius was 6366 km. Where K is the Gaussian curvature, 2 This cookie is set by GDPR Cookie Consent plugin. The meridional mean is well approximated by the semicubic mean of the two axes,[citation needed]. Wind farms have different impacts on the environment compared to conventional power plants, but similar concerns exist over both the noise produced by the turbine blades and the . To determine the diameter of the earth in metres first multiply the original value by 2. Mass of planet M = 8 x mass of earth = 8 x 6 x 10 24 kg. Given you're looking for a simple formula, this is probably the simplest way to do it, assuming that the Earth is a sphere with a circumference of 40075 km. As an example, we will use Eratosthenes measurements. Thus the curvature found this way is smaller than the curvature of a circle of constant latitude, except at the equator. What is the earths radius in meters?Earth radiusSI base unit6.3781106 mMetric system6,357 to 6,378 kmEnglish units3,950 to 3,963 miEarth radiusSI base unit6.3781106 mMetric system6,357 to 6,378 kmEnglish units3,950 to 3,963 miWhat is the radius of the earth?According to data taken by 183 high-school classes participating in a World Year of Physics project, "Measure the Earth y New Arrivals Expand Space Stations Crew to 6. Above we see an object with mass m attached to a spring. The radius R of a nucleus of mass number A can be estimated by the formula R = (1.3 1015)A 1/3 m. The earth rotates once every 23 hours, 56 minutes and 4.09053 seconds, called the sidereal period, and its circumference is roughly 40,075 kilometers. Solution for the radious of earth is 6378.1 km, which is 2981.1 km greater than the radius of mars. c) Calculate the gravitational potential energy associated with a 4.93-kg object at the r = 39350/ 6.28 = 6267 kilometer. What does EARTH RADIUS mean? Note that this arc is along a great circle. Likewise for surface area, either based on a map projection or a geodesic polygon. det He was the first one to use the word geography and he also had a small-scale notion of the planet that helped him to determine the circumference of the earth. The circumference of the Earth depends on how it is measured. Ocean Worlds Resources. , find the radius of mars. Eastwest directions can be misleading. [ What is the formula of radius of nucleus? Refer to the WGS-84 ellipsoid if a more precise value for its polar radius is needed. Your partner should measure at the same time, regardless of time difference. Earth's diameter is simply twice Earth's radius; for example, equatorial diameter (2a) and polar diameter (2b). The first person to determine the size of Earth was Eratosthenes of Cyrene, who produced a surprisingly good measurement using a simple scheme that combined geometrical calculations with physical observations. Thus, the surface of the earth at the. [13], Earth's authalic radius (meaning "equal area") is the radius of a hypothetical perfect sphere that has the same surface area as the reference ellipsoid. earthRadius But opting out of some of these cookies may affect your browsing experience. Has got the radius of Earth mysteriously grown by about 3%? N [29] To settle the matter, the French Geodesic Mission (17351739) measured one degree of latitude at two locations, one near the Arctic Circle and the other near the equator. , which is defined to be 6,378.1km (3,963.2mi). [27] However, the 1492 enactment of that voyage brought his fleet to the Americas. 06. Chapter P, Problem 13E is solved. A) 4.5 x 10-7 B) 4.5 x 107 C) 45 x 10-6 D) 45 x 106 The geocentric radius is the distance from the Earth's center to a point on the spheroid surface at geodetic latitude : where a and b are, respectively, the equatorial radius and the polar radius. This idea predates satellite-based geodesy by centuries. However, other factors such as the rotation of the Earth also contribute to the net acceleration. 2019 11:40, yfnal3x. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly 6,378km (3,963mi) (equatorial radius, denoted a) to a minimum of nearly 6,357km (3,950mi) (polar radius, denoted b). This answer is: K Do NOT follow this link or you will be banned from the site! The WGS84 ellipsoid can be used worldwide (such as the ridiculously over-precise flattening value). MITs Alan , In 2020, as a response to the disruption caused by COVID-19, the College Board modified the AP exams so they were shorter, administered online, covered less material, and had a different format than previous tests. The planet's rotation causes it to bulge at the equator. Earths Equatorial Radius to Meter Conversion Table, How to Convert Earths Equatorial Radius to Meter, Convert Earths Equatorial Radius to Other Length Units. If one point had appeared due east of the other, one finds the approximate curvature in the eastwest direction. Scholars have interpreted Aristotle's figure to be anywhere from highly accurate[20] to almost double the true value. (e) For that Earth 1/q 289, that is near to the measured inverse flattening 1/f 298. Use a scientific calculator. Venus is included with a thick, quickly spinning atmosphere, developing a scorched world with temperatures hot enough to melt lead along with a surface pressure 90 occasions those of Earth. 3 He observed lunar eclipses and noticed that only a round sphere could imply a circular shadow. What is the radius of Earth in gravitation? close. Example 2. The value for the polar radius in this section has been rounded to the nearest 0.1m, which is expected to be adequate for most uses. T he circumference of the Earth (around the equator) is approximately 24,887 miles. Initially, the idea of a reference ellipsoid was an ellipsoid that best approximated mean ocean level. The tropical radius of the world (or semi-major axis) is all about 6,378 km (3,963 miles or 3,444 maritime miles), as the polar radius of the world (or semi-minor axis) is all about 6,357 km (3,950 miles or 3,432 maritime miles). This video will show you how Eratosthenes calculated the circumference and radius of the Earth in 240 BC!! Also see the Table of Physical Units and Constants. .[10]. Her latest book, "A Travel for Taste: Germany," was published in 2015. Solution Verified 2 The adolescent protagonists of the sequence, Enrique and Rosa, are Arturos son and , The payout that goes with the Nobel Prize is worth $1.2 million, and its often split two or three ways. {\displaystyle {\mathcal {R}}_{\mathrm {pJ} }^{\mathrm {N} }} The space station is 356 feet (109 meters) end-to-end, one yard shy of the full length of an American football field including the end . {\displaystyle p=N\cos(\varphi )} Regarding this, what is the diameter of the Earth in scientific notation? which is different from the precise result by under 1m (4105in) the mean of these two axes. At room temperature, it will go from a solid to a gas directly. N Its mean density is 1410 kg/m 3 or 0.255 times the mean density of Earth. Using the curvature of the Earth relative to the parallel light from the sun, we can observe shadows at different locations on the surface of the Earth to find the Earths radius. The radius of the earth is 6371 km. for an oblate spheroid, the curvatures are. Definitions and Formulas. Our descriptions of Earths surface must be simpler than reality in order to be tractable. This is the outside layer of the earth and is made of solid rock, mostly basalt and granite. Because these measurements are not done with more sensitive equipment, the radius calculation will be only approximate. What is the radius of the parallel of latitude? In scientific notation, the radius of the earth in meters is equal to 6.37106 meters or approximately 6.4106 meters, and 6378100 or approximately 6370000 in standard form. Place the loose end of the string at the end of the cast shadow and hold it taut. w (clarification needed). The planet bulges at the equator as a result of its rotation. Like a torus, the curvature at a point will be greatest (tightest) in one direction (northsouth on Earth) and smallest (flattest) perpendicularly (eastwest). The other two are the radii of curvature. . Given local and transient influences on surface height, the values defined below are based on a "general purpose" model, refined as globally precisely as possible within 5m (16ft) of reference ellipsoid height, and to within 100m (330ft) of mean sea level (neglecting geoid height). The Earths circumference is approximately 40,000,000 meters. The distance between Syene and Alexandria is 787 kilometers. N example R = earthRadius (lengthUnit) returns the mean radius of the Earth using the length unit specified by lengthUnit. NASA Telescope Takes 12-Year Time-Lapse Movie of Entire Sky. Additionally, the radius can be estimated from the curvature of the Earth at a point. R = earthRadius returns the scalar value 6,371,000, the mean radius of the Earth in meters. 1 Earths equatorial radius637816 m1 Earths equatorial radius6378160 m2 Earths equatorial radius12756320 m3 Earths equatorial radius19134480 m5 Earths equatorial radius31890800 m10 Earths equatorial radius63781600 m20 Earths equatorial radius127563200 m50 Earths equatorial radius318908000 m100 Earths equatorial radius637816000 m1000 Earths equatorial radius6378160000 mHow to Convert Earths Equatorial Radius to Meter1 Earths equatorial radius = 6378160 m1 m = 1. e When he's not busy exploring the mysteries of the universe, George enjoys hiking and spending time with his family. , For Earth, the volumetric radius equals 6,371.0008km (3,958.7564mi). [a] Local topography increases the variance, resulting in a surface of profound complexity. University of Texas: Eratosthenese Finds Diameter of Earth, Partner in a distant location on about the same longitude or in the same time zone. Q4. The model is rotated in a wind tunnel at a rotational speed of 500 rev/minrev/min. Wittenberg is a nationally ranked liberal arts institution with a particular strength in the sciences. We invite readers to visit us daily, explore topics of interest, and gain new perspectives along the way. is the eccentricity of the earth. What is the radius of Earth in exponential form? 1 Does Bohrs model explain radius of an orbit? This topographical average is 6,371.230km (3,958.899mi) with uncertainty of 10m (33ft).[16]. r . How do you find the radius of a planet in physics? High School Students Measure New Value for Earths Radius to Celebrate World Physics Year. 2 R The radius of earth, is the distance from the centre of the Earth to a point on or near its surface, and it ranges from nearly 6,378 km to nearly 6,357 km, dhanyaranjan Published On January 28th, 2022 Table of Contents Radius of Earth in Physics The symbol R? So escape velocity of the planet will be 22.4 km/sec Measuring the Circumference of the Earth. See answer. The average radius of the earth is 6.38x106 meters. This table summarizes the accepted values of the Earth's radius. [4], The variation in density and crustal thickness causes gravity to vary across the surface and in time, so that the mean sea level differs from the ellipsoid. [7] Additional discrepancies caused by topographical variation at specific locations can be significant. The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". (a) To what radius (in meters) would the earth have to be compressed in order for it to become a black holethe escape velocity from its surface equal to the velocity c = 3 \times 10 ^ { 8 } \mathrm { m } / \mathrm { s } c = 3108m/s of light? Regardless of the model, any radius falls between the polar minimum of about 6,357km and the equatorial maximum of about 6,378km (3,950 to 3,963mi). Hence, we create models to approximate characteristics of Earth's surface, generally relying on the simplest model that suits the need. ] Write it in scientific notation. When it is measured around the equator, it is40,075 km (approximately, 24,901 miles), whereas, if it measured from the north pole to the south pole it is40,008 km (approximately, 24,860 miles). The cookie is used to store the user consent for the cookies in the category "Other. ] Copyright 2022 - Science-Atlas.com. What is the real radius of the earth? Keplers Third law can be used to determine the orbital radius of the planet if the mass of the orbiting star is known (R3=T2Mstar/Msun, the radius is in AU and the period is in earth years). It is the only planet in our solar system that sustains life and it is the planet that we can call our own. In 200 B.C. You can do this, too, by using his method. This equation for acceleration can , Dry ice is the name for carbon dioxide in its solid state. 2 degrees. Answer: Starter The radius of the moon is 1,737,000 meters. Nowadays there are better ellipsoids when it comes to supplying a much better fit to mean ocean level compared to WGS84 ellipsoid. {\displaystyle w^{2}=\lambda ,}. Geodetic ellipsoids are better suited to regional idiosyncrasies of the geoid. Responsibility disclaimer and privacy policy | About Us | Terms & Conditions | Site Map, Scientific discoveries from around the world. All Right Reserved. = As such, they are topographical geocentric distances, Rt, which depends not only on latitude. Around 1690, Isaac Newton and Christiaan Huygens argued that Earth was closer to an oblate spheroid than to a sphere. Venus is covered by a thick, rapidly spinning atmosphere, creating a scorched world with temperatures hot enough to melt lead and a surface pressure 90 times that of Earth. \text{Circumference} = 39,350 \text{\ kilometers}. [1]:4 What is the permiter of the Earth? Its the only planet with life. That's between 28 and 29 Earths. The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. This difference is the geoid height, positive above or outside the ellipsoid, negative below or inside. Step 2 of 5. Start your trial now! About Earth radiusThe Earth radius, or even the radius of the world, may be the distance from the middle of our planet towards the surface. Born and raised in the city of London, Alexander Johnson studied biology and chemistry in college and went on to earn a PhD in biochemistry. Thus, the surface of the earth at the equator moves at a speed of 460 meters per secondor roughly 1,000 miles per hour. f In simple words, radius refers to that line, which originates from any point of the circle and touches the centre point the circle. = 6,356.8km (3,949.9mi). According to Newtons second law of motion, the acceleration of an object equals the net force acting on it divided by its mass, or a = F m . What is the radius of the parallel of latitude? ( It is a common misconception that Terra is the internationally-recognized scientific name of the planet, but in reality Earth does not have an official international name. The diameter is the distance from side to side, if you. After completing his degree, George worked as a postdoctoral researcher at CERN, the world's largest particle physics laboratory. Now, lets plug in some numbers. nasa.gov. {\displaystyle {\mathcal {R}}_{\mathrm {eE} }^{\mathrm {N} }} The standard English name of the planet, including in science, is Earth. . Then convert km - m. 1 km = 1000 m. 12 756 km = ? R Earth, on the other hand, isn't quite a sphere. By knowing the Equatorial diameter or the polar diameter of the Earth, the circumference can be found. If we were to plot this it would show (setting, G = M = m = R = 1, and including force direction): A simple spring oscillator To understand what this means we'll look at a simple spring oscillator. Earth radius Conversion conversion table Earth radius to Meters Conversion Table Meters [ m ] All other parallels of latitude are small circles, each having a radius smaller than that of the earth, i.e. Eratosthenes methods result in a formula that would look like this: 39,350 = 2 x 3.14 x r, or 6,267 kilometers. Earth, as we know now, is an oblate spheroid, as shown in the above figure. The typical radius of the world is roughly 6. less than 6400 km. The following is a partial list of models of Earth's surface, ordered from exact to more approximate: In the case of the geoid and ellipsoids, the fixed distance from any point on the model to the specified center is called "a radius of the Earth" or "the radius of the Earth at that point". How do you find the radius of a planet in physics? Necessary cookies are absolutely essential for the website to function properly. [e] For the Earth .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num,.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0 0.1em}.mw-parser-output .sfrac .den{border-top:1px solid}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}1/q 289, which is close to the measured inverse flattening 1/f 298.257. Video advice: What is EARTH RADIUS? 6378 X 2 = 12 756 km. Derivation means the action of obtaining something from a source or origin. When identifying the position of an observable location, the use of more precise values for WGS-84 radii may not yield a corresponding improvement in accuracy. A closed-form solution exists for a spheroid:[14]. That's almost 32 Earths. in the second fundamental form for a surface (Equation (123) in[11]): e, f, and g are elements of the shape tensor: n The polar radius of the Earth is 3,950 miles (6,356), which is a 13-mile (22-kilometer) difference. Earth's volume is estimated at 1 trillion cubic kilometers. When the Moon is the farthest away, it's 252,088 miles away. arrow_forward. The orbit is not a perfect circle. In this state, it would have approximately the same mass as it has now, but its radius would be equal to the radius of the Earth. For this calculation, the longitude isn't needed. The bulge had been decreasing, but since 1998 the bulge has increased, possibly due to redistribution of ocean mass via currents. For information on the Earth, see the Earth Fact Sheet. r . The radius of the earth's orbit is 45,000,000 meters. 64miles, whereas, whether it ismeasured round the rods, it isapproximately 24,806 miles. An Enormous, Unknown Cambrian Bug Fossil Has Been Discovered within the Eerie Burgess Shale, Ancient Tracks May Be The Oldest Hominin Footprints Ever Found, Scientists Say, By 2500, Earth Will Be Alien To Humans If We Dont Act Now, Scientists Warn, Responsibility disclaimer and privacy policy, Topics Related to Circumference of the Earth. p Asked By: Lena Frontelo | Last Updated: 18th May, 2020, Earth is the third planet from the sun. A nominal Earth radius is sometimes used as a unit of measurement in astronomy and geophysics, which is recommended by the International Astronomical Union to be the equatorial value.[1]. Let the mass of the earth be M and radius of the earth be R, The distance of the body from the center of the earth will also be equal to the radius R of the earth. What is the Radius of the Earth? But opting out of some of these cookies may affect your browsing experience. The physical radius, the distance from the center of the earth to the ellipsoid is the least used. Using the Gauss-Bonnet theorem, this gives, Another spherical model is defined by the Earth's volumetric radius, which is the radius of a sphere of volume equal to the ellipsoid. Multiplyin. 371 106 m), the bottom unit of length within the Worldwide System of Units (SI). However, Earth is not quite a sphere. As , EL NORTE is a melodrama divided into three acts. For a perfect sphere without any mountains, the distance d from a transmitting antenna to the horizon or the line of sight, or radio horizon, can be calculated from the Pythagorean theorem (see the picture above):. However, around 1730, Jacques Cassini argued for a prolate spheroid instead, due to different interpretations of the Newtonian mechanics involved. Earths radius is usually given as 6378137 meters (equatorial radius), its flattening is defined as 1/298.257223 (WGS84), and thus its polar radius is calculated as 6356752 meters.However, the av. Other ways to define and measure the Earth radius involve the radius of curvature. {\displaystyle {\mathcal {R}}_{\mathrm {pE} }^{\mathrm {N} }} How do you find the radius in circular motion? Therefore, the difference was 7.2 degrees. The following radii are derived from the World Geodetic System 1984 (WGS-84) reference ellipsoid. As the parallels run east and west, places having the same latitude will be due east or due west of each other. wikipedia article on the Juno spacecraft provides an a great overview of this type of process. 01 Earths equatorial radius63781. How do you find the acceleration of a system? {\displaystyle w^{1}=\varphi } 7564mi). Radius of planet R = 2 x radius of earth = 2 x 6.4 x 10 6 m. G = gravitational constant = 6.67 x 10-11 N m 2 /kg 2. The radius of a circle is the straight-line distance from the very center of the circle to any point on the circle. Unless you know indoor location is available inside the geofence, assume that Wi-Fi . How cold is it on moon? It is a physical constant which represents the most probable distance between the electron and the nucleus in a hydrogen atom in its ground state. He also shares personal stories and insights from his own journey as a scientist and researcher. 2013-09-16 00:47:38. The bulge have been decreasing, consider 1998 the bulge has elevated, possibly because of redistribution of sea mass via currents. "The Earth's mass is about 5.98 10 24 kg". where e2 = a2 b2/a2 and A is the surface area of the spheroid. The radius of Earth at the equator is 3,963 miles (6,378 kilometers), according to NASA's Goddard Space Flight Center in Greenbelt, Maryland. {\displaystyle r=[r^{1},r^{2},r^{3}]^{T}=[x,y,z]^{T}} Eratosthenes was born around 276 B.C., which is now Shahhat, Libya. The first published reference to the Earths size appeared around 350BC, when Aristotle reported in his book On the Heavens(18) that mathematicians had guessed the circumference of the Earth to be 400,000 stadia. What is the radius of Earth in meters? which differs from the exact result by less than 1m (4105in); the mean of the two axes. On solving the circumference of the earth we get 39,350 kilometres. Physics, 22. Have your partner do the same in her location. There are two types of crust; oceanic and continental. Find the level of Earth in cubic meters. How do you find the radius of the Earth using trigonometry? When we rearrange the equation and plug all the numbers in, we find that the mass of the Earth is 5.96 1024 kg. One reason that our program is so strong is that our . , g = GM/r2, Where M is the mass of the Earth, r the radius of the Earth (or distance between the center of the Earth and you, standing on its surface), and G is the gravitational constant. = Acceleration due to gravity is a vector, which means it has both a magnitudeand a direction. Our Planet radius is really a unit of distance utilized in astronomy and geology. The radius of orbit indicates the distance that the satellite is from the center of the earth. It is with the values I gave you. Geometrically, the second fundamental form gives the distance from Eratosthenes, the ancient Greek scholar is called the father of geography. As a consequence of this, the polar radius is closer to 6,356.7 kilometers. ), In geophysics, the International Union of Geodesy and Geophysics (IUGG) defines the Earth's arithmetic mean radius (denoted R1) to be[2], The factor of two accounts for the biaxial symmetry in Earth's spheroid, a specialization of triaxial ellipsoid. A cylinder has a radius of 8 meters. A sphere being a gross approximation of the spheroid, which itself is an approximation of the geoid, units are given here in kilometers rather than the millimeter resolution appropriate for geodesy. Each of the models in common use involve some notion of the geometric radius. | We must convert the radius into centimeters: R Moon = 1738 km X (1000m / km) X (100cm / m) = 1.738 X 10 8 cm. At the poles, = 90o and the length = 110.95 km, nearly. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. F The equatorial circumference is simply the circle perimeter: Ce=2a, in terms of the equatorial radius, a. to the plane tangent at What is the number in scientific notation? In the third century B.C., Eratosthenes was able to mathematically calculate the earths diameter by comparing differences in the angle of the suns rays at two separate geographic points. In 1993 the WGS84 governing committee voted, with one exception, to retain the 1984 defining values, despite improvements to those defining values. The total mass of all the asteroids combined is less than that of Earth's Moon. to have an oblate spheroid, the curvatures are. For Eratosthenes, at midday on the summer solstice where the suns angle was directly overhead, the angle was zero. The Earth. mpanderla95. When it's closest, the Moon is 225,623 miles away. Enchanted Learning. Radius of sun is 695 500 km, so in meters you multiply by 1000. The actual radius of the earth is 6,378.1 kilometers at the equator, but the radius varies because the earth is a somewhat flattened sphere. The expedition found that Newton's conjecture was correct:[30] the Earth is flattened at the poles due to rotation's centrifugal force. For integration limits of [0,/2], the integrals for rectifying radius and mean radius evaluate to the same result, which, for Earth, amounts to 6,367.4491km (3,956.5494mi). Equatorial radius is conventionally used as the nominal value unless the polar radius is explicitly required. The corresponding radius of curvature depends on the location and direction of measurement from that point. (a) Local topography increases the variance, resulting in a surface of profound complexity. Because the Earth isnt perfectly spherical but instead an oblate spheroid, our planet radius is larger in the equator than in the rods. January 2023: The Next Full Moon is the Wolf or Ice Moon. As satellite remote sensing and especially the Global Positioning System gained importance, true global models were developed which, while not as accurate for regional work, best approximate the Earth as a whole. Drive one of the meter sticks into the ground in your location in a sunny spot. In a geocentric ellipsoid, the center of the ellipsoid coincides with some computed center of Earth, and best models the earth as a whole. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.