1.
Ambigram
–
An ambigram is a word, art form or other symbolic representation whose elements retain meaning when viewed or interpreted from a different direction, perspective, or orientation. The meaning of the ambigram may either change, or remain the same, Douglas R. Hofstadter describes an ambigram as a calligraphic design that manages to squeeze two different readings into the selfsame set of curves. Different ambigram artists may create completely different ambigrams from the word or words. The earliest known non-natural ambigram dates to 1893 by artist Peter Newell, the last page in his book Topsys & Turvys contains the phrase THE END, which, when inverted, reads PUZZLE. In Topsys & Turvys Number 2, Newell ended with a variation on the ambigram in which THE END changes into PUZZLE2, from June to September,1908, the British monthly The Strand published a series of ambigrams by different people in its Curiosities column. Of particular interest is the fact all four of the people submitting ambigrams believed them to be a rare property of particular words. In 1969, Raymond Loewy designed the rotational NEW MAN ambigram logo, the mirror ambigram DeLorean Motor Company logo was first used in 1975. John Langdon and Scott Kim also each believed that they had invented ambigrams in the 1970s, Langdon and Kim are probably the two artists who have been most responsible for the popularization of ambigrams. John Langdon produced the first mirror image logo Starship in 1975, Robert Petrick, who designed the invertible Angel logo in 1976, was also an early influence on ambigrams. The earliest known published reference to the term ambigram was by Hofstadter, the original 1979 edition of Hofstadters Gödel, Escher, Bach featured two 3-D ambigrams on the cover. Langdon also produced the ambigram that was used for versions of the books cover. Brown used the name Robert Langdon for the hero in his novels as an homage to John Langdon, in music, the Grateful Dead have used ambigrams several times, including on their albums Aoxomoxoa and American Beauty. In the first series of the British show Trick or Treat and these cards can read either Trick or Treat. The Transformers movie series have logos that are a robot face whether viewed right side up or upside down, there are two such logos, one for an Autobot, and one for a Decepticon. In 2015 iSmarts logo on one of its travel chargers went viral because upside-down it read +Jews. The company noted that. we learned a lesson of what not to do when creating a logo. ”Ambigrams are exercises in graphic design that play with optical illusions, symmetry. Some ambigrams feature a relationship between their form and their content, ambigrams usually fall into one of several categories, 3-Dimensional A design where an object is presented that will appear to read several letters or words when viewed from different angles. Such designs can be generated using constructive solid geometry, chain A design where a word are interlinked, forming a repeating chain

2.
Coriolis force
–
In physics, the Coriolis force is an inertial force that acts on objects that are in motion relative to a rotating reference frame. In a reference frame with clockwise rotation, the acts to the left of the motion of the object. In one with anticlockwise rotation, the acts to the right. Early in the 20th century, the term Coriolis force began to be used in connection with meteorology, deflection of an object due to the Coriolis force is called the Coriolis effect. Newtons laws of motion describe the motion of an object in a frame of reference. When Newtons laws are transformed to a frame of reference. Both forces are proportional to the mass of the object, the Coriolis force is proportional to the rotation rate and the centrifugal force is proportional to its square. The Coriolis force acts in a perpendicular to the rotation axis. The centrifugal force acts outwards in the direction and is proportional to the distance of the body from the axis of the rotating frame. These additional forces are termed inertial forces, fictitious forces or pseudo forces and they allow the application of Newtons laws to a rotating system. They are correction factors that do not exist in a non-accelerating or inertial reference frame, a commonly encountered rotating reference frame is the Earth. The Coriolis effect is caused by the rotation of the Earth, such motions are constrained by the surface of the Earth, so only the horizontal component of the Coriolis force is generally important. This force causes moving objects on the surface of the Earth to be deflected to the right in the Northern Hemisphere, the horizontal deflection effect is greater near the poles, since the effective rotation rate about a local vertical axis is largest there, and smallest at the equator. This effect is responsible for the rotation of large cyclones, riccioli, Grimaldi, and Dechales all described the effect as part of an argument against the heliocentric system of Copernicus. In other words, they argued that the Earths rotation should create the effect, the effect was described in the tidal equations of Pierre-Simon Laplace in 1778. Gaspard-Gustave Coriolis published a paper in 1835 on the yield of machines with rotating parts. That paper considered the forces that are detected in a rotating frame of reference. Coriolis divided these forces into two categories

3.
Revolving door
–
A revolving door typically consists of three or four doors that hang on a central shaft and rotate around a vertical axis within a cylindrical enclosure. Revolving doors are energy efficient as they prevent drafts, thus preventing increases in the heating or cooling required for the building, at the same time, revolving doors allow large numbers of people to pass in and out. Around the central shaft of the door, there are usually three or four panels called wings or leaves. Large diameter revolving doors can accommodate strollers and wheeled luggage racks, the tallest revolving door in Europe is currently 5. 2m high with 4 wings. Some revolving door displays incorporate a small enclosure, permitting small objects such as sculpture, fashion mannequins. Such enclosures can either be mounted at the pivot, or attached to the revolving door wings. The wings of revolving doors usually incorporate glass, to people to see. Manual revolving doors rotate with pushbars, causing all wings to rotate, Revolving doors typically have a speed control to prevent people from spinning the doors too fast. Automatic revolving doors are powered above/below the central shaft, or along the perimeter, automatic revolving doors have safety sensors, but there has been at least one fatality recorded. Normally, the door is always closed so that wind and drafts cannot blow into the building, to efficiently minimize heating. In right hand traffic countries, revolving doors typically revolve counter-clockwise, allowing people to enter, in left hand traffic countries such as Australia and New Zealand, revolving doors revolve clockwise, but door rotations are mixed in Britain. Direction of rotation is often enforced by the governor mechanism. Revolving doors can also be used as security devices to restrict entry to a person at a time if the spacing between the doors is small enough. This is in contrast to a door which allows a second person to easily tailgate behind an authorized person. Extreme security can require bullet-proof glass, sometimes a revolving door is designed for one-way traffic. An example is the usage in airports to prevent a person from bypassing airport security checkpoints by entering the exit. Such doors are designed with a brake that is activated by a sensor should someone enter from the incorrect side, the door also revolves backwards to permit that person to exit, while also notifying security of the attempt. Turnstile exit-only doors are often used in subways and other rapid transit facilities to prevent people from bypassing fare payment

4.
Moment of inertia
–
It depends on the bodys mass distribution and the axis chosen, with larger moments requiring more torque to change the bodys rotation. It is a property, the moment of inertia of a composite system is the sum of the moments of inertia of its component subsystems. One of its definitions is the moment of mass with respect to distance from an axis r, I = ∫ Q r 2 d m. For bodies constrained to rotate in a plane, it is sufficient to consider their moment of inertia about a perpendicular to the plane. When a body is rotating, or free to rotate, around an axis, the amount of torque needed to cause any given angular acceleration is proportional to the moment of inertia of the body. Moment of inertia may be expressed in units of kilogram metre squared in SI units, moment of inertia plays the role in rotational kinetics that mass plays in linear kinetics - both characterize the resistance of a body to changes in its motion. The moment of inertia depends on how mass is distributed around an axis of rotation, for a point-like mass, the moment of inertia about some axis is given by mr2, where r is the distance to the axis, and m is the mass. For an extended body, the moment of inertia is just the sum of all the pieces of mass multiplied by the square of their distances from the axis in question. For an extended body of a shape and uniform density. In 1673 Christiaan Huygens introduced this parameter in his study of the oscillation of a body hanging from a pivot, the term moment of inertia was introduced by Leonhard Euler in his book Theoria motus corporum solidorum seu rigidorum in 1765, and it is incorporated into Eulers second law. Comparison of this frequency to that of a simple pendulum consisting of a single point of mass provides a mathematical formulation for moment of inertia of an extended body. Moment of inertia appears in momentum, kinetic energy, and in Newtons laws of motion for a rigid body as a physical parameter that combines its shape. There is a difference in the way moment of inertia appears in planar. The moment of inertia of a flywheel is used in a machine to resist variations in applied torque to smooth its rotational output. Moment of inertia I is defined as the ratio of the angular momentum L of a system to its angular velocity ω around a principal axis, if the angular momentum of a system is constant, then as the moment of inertia gets smaller, the angular velocity must increase. This occurs when spinning figure skaters pull in their arms or divers curl their bodies into a tuck position during a dive. For a simple pendulum, this yields a formula for the moment of inertia I in terms of the mass m of the pendulum and its distance r from the pivot point as. Thus, moment of inertia depends on both the mass m of a body and its geometry, or shape, as defined by the distance r to the axis of rotation

5.
Parbuckle salvage
–
Parbuckle salvage, or parbuckling, is the righting of a sunken vessel using rotational leverage. A common operation with smaller watercraft, parbuckling is also employed to right large vessels, while the mechanical advantage used by the laborer to parbuckle a cask up an incline is 2,1, parbuckling salvage is not so limited. Each of the 21 winches used to roll the Oklahoma used cables that passed through two 17-part tackle assemblies, eight 28-inch diameter sheaves, eight 24-inch diameter sheaves, and one 20-inch diameter sheave comprised just half the mechanical effort. A major concern during salvage is preventing rotational torque from becoming a force moving the ship sideways. USS Utah, lost like the Oklahoma in the Pearl Harbor attack, was meant to be recovered by a similar rotation after the Oklahoma, as the Utah was rotated, however, its hull did not catch on the harbor bottom, and the vessel slid towards Ford Island. The Utah recovery effort was abandoned, Oklahoma weighed about 35,000 short tons. Twenty-one electric winches were installed on Ford Island, anchored in concrete foundations, each winch pulled about 20 short tons by a wire operated through a block system which gave an advantage of seventeen, for a total pull of 21×20×17, or 7,140 short tons. In order to increase the leverage, the passed over a wooden strut arrangement which stood on the bottom of the ship about 40 feet high. Oil had been removed from the ship through the bottom, the ship was lightened by air inside the hull. There was an amount of weight in the ship which may have been removed prior to righting. About one-third of the ammunition was taken off together with some of the machinery, the blades of the two propellers were also taken off, but more to avoid damage to them than to reduce weight. Tests were made to check whether restraining forces should be used to prevent sliding toward Ford Island and it was indicated that the soil under the aft part of the ship prevented sliding, whereas the bow section rested in soupy mud which permitted it. To prevent sliding about 2200 tons of soil were deposited near the bow section. During righting, excess soil under the side was washed away by high-pressure jets operated by divers. The ship rolled as it should have and was right-side up by 16 June 1943, the mean draft of the ship after righting was c.50 feet. Tensioning the cables started the roll of the ship, at about the halfway-to-vertical position the sponsons were filled with seawater, and Costa Concordia completed its roll to upright upon the ledge. The hull was rotated 65 degrees to become vertical, the holdback system consisted of 56 chains in total, of which 22 chains were attached to the port side to go under the hull to the island. Each chain was 58 meters long and weighed about 26 metric tons, the ledge was part steel and part grout

6.
Rotating wheel space station
–
A rotating wheel space station is a hypothetical wheel-shaped space station that rotates about its axis, thus creating an environment of artificial gravity. In principle, the station could be configured to simulate the gravitational acceleration of Earth, both scientists and science fiction writers have thought about the concept of a rotating wheel space station since the beginning of the 20th century. Konstantin Tsiolkovsky wrote about using rotation to create a gravity in space in 1903. Herman Potočnik introduced a spinning wheel station with a 30 meter diameter in his Problem der Befahrung des Weltraums and he even suggested it be placed in a geostationary orbit. In the 1950s, Wernher von Braun and Willy Ley, writing in Colliers Magazine, updated the idea and they envisioned a rotating wheel with a diameter of 76 meters. The 3-deck wheel would revolve at 3 RPM to provide artificial one-third gravity and it was envisaged as having a crew of 80. In 1959, a NASA committee opined that such a station was the next logical step after the Mercury program. The Stanford torus, proposed by NASA in 1975, is a version of the same concept. NASA has never attempted to build a rotating space station. First, such a station would be difficult to construct, given the limited lifting capability available to the United States. Assembling such a station and pressurizing it would present formidable obstacles, second, NASA considers the present space station, the ISS, to be valuable as a zero gravity laboratory, and its current microgravity environment was a conscious choice. More recently, NASA has explored plans for a Nautilus X centrifuge demonstration project, if flown, this would add a centrifuge sleep quarters module to the ISS. This makes it possible to experiment with artificial gravity without destroying the usefulness of the ISS for zero g experiments and it could lead to deep space missions under full g in centrifuge sleeping quarters following the same approach. Many space stations and ships use a rotating design, clarkes novel 2001, A Space Odyssey was developed concurrently with Stanley Kubricks film version of 2001. In it, the space station Space Station V provides artificial gravity. 1985, The novel Enders Game features a station, called Battle School. As the characters ascend through the station towards the center, there is a decline in the feeling of gravity. 1999, The Japanese manga and anime Planetes has its main set in The Seven, the 7th wheel orbital station

7.
Earth's rotation
–
Earths rotation is the rotation of the planet Earth around its own axis. The Earth rotates from the west towards east, as viewed from North Star or polestar Polaris, the Earth turns counter-clockwise. The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earths axis of rotation meets its surface and this point is distinct from the Earths North Magnetic Pole. The South Pole is the point where the Earths axis of rotation intersects its surface. The Earth rotates once in about 24 hours with respect to the sun, Earths rotation is slowing slightly with time, thus, a day was shorter in the past. This is due to the effects the Moon has on Earths rotation. Atomic clocks show that a modern-day is longer by about 1.7 milliseconds than a century ago, analysis of historical astronomical records shows a slowing trend of 2.3 milliseconds per century since the 8th century BCE. Among the ancient Greeks, several of the Pythagorean school believed in the rotation of the rather than the apparent diurnal rotation of the heavens. Perhaps the first was Philolaus, though his system was complicated, in the third century BCE, Aristarchus of Samos suggested the suns central place. However, Aristotle in the fourth century criticized the ideas of Philolaus as being based on rather than observation. He established the idea of a sphere of fixed stars that rotated about the earth and this was accepted by most of those who came after, in particular Claudius Ptolemy, who thought the earth would be devastated by gales if it rotated. In the 10th century, some Muslim astronomers accepted that the Earth rotates around its axis, treatises were written to discuss its possibility, either as refutations or expressing doubts about Ptolemys arguments against it. At the Maragha and Samarkand observatories, the Earths rotation was discussed by Tusi and Qushji, in medieval Europe, Thomas Aquinas accepted Aristotles view and so, reluctantly, did John Buridan and Nicole Oresme in the fourteenth century. Not until Nicolaus Copernicus in 1543 adopted a heliocentric world system did the earths rotation begin to be established, Copernicus pointed out that if the movement of the earth is violent, then the movement of the stars must be very much more so. He acknowledged the contribution of the Pythagoreans and pointed to examples of relative motion, for Copernicus this was the first step in establishing the simpler pattern of planets circling a central sun. Tycho Brahe, who produced accurate observations on which Kepler based his laws, in 1600, William Gilbert strongly supported the earths rotation in his treatise on the earths magnetism and thereby influenced many of his contemporaries. Those like Gilbert who did not openly support or reject the motion of the earth about the sun are often called semi-Copernicans, however, the contributions of Kepler, Galileo and Newton gathered support for the theory of the rotation of the Earth. The earths rotation implies that the bulges and the poles are flattened

8.
Mechanics of planar particle motion
–
This article describes a particle in planar motion when observed from non-inertial reference frames. The most famous examples of motion are related to the motion of two spheres that are gravitationally attracted to one another, and the generalization of this problem to planetary motion. See centrifugal force, two-body problem, orbit and Keplers laws of planetary motion and those problems fall in the general field of analytical dynamics, the determination of orbits from given laws of force. This article is focused more on the issues surrounding planar motion. The Lagrangian approach to fictitious forces is introduced, unlike real forces such as electromagnetic forces, fictitious forces do not originate from physical interactions between objects. The appearance of fictitious forces normally is associated with use of a frame of reference. For solving problems of mechanics in non-inertial reference frames, the advice given in textbooks is to treat the fictitious forces like real forces, elaboration of this point and some citations on the subject follow. Examples are Cartesian coordinates, polar coordinates and curvilinear coordinates, or as seen from a rotating frame. A time-dependent description of observations does not change the frame of reference in which the observations are made, in discussion of a particle moving in a circular orbit, in an inertial frame of reference one can identify the centripetal and tangential forces. It then seems to be no problem to switch hats, change perspective and that switch is unconscious, but real. Suppose we sit on a particle in planar motion. What analysis underlies a switch of hats to introduce fictitious centrifugal, to explore that question, begin in an inertial frame of reference. In Figure 1, the arc length s is the distance the particle has traveled along its path in time t, the path r with components x, y in Cartesian coordinates is described using arc length s as, r =. One way to look at the use of s is to think of the path of the particle as sitting in space, like the left by a skywriter. Any position on this path is described by stating its distance s from some starting point on the path, then an incremental displacement along the path ds is described by, d r = = d s, where primes are introduced to denote derivatives with respect to s. The magnitude of this displacement is ds, showing that, =1, the unit magnitude of these vectors is a consequence of Eq.1. As an aside, notice that the use of vectors that are not aligned along the Cartesian xy-axes does not mean we are no longer in an inertial frame. All it means is that we are using unit vectors that vary with s to describe the path, the radius of curvature is introduced completely formally as,1 ρ = d θ d s

9.
Rotations in 4-dimensional Euclidean space
–
In mathematics, the group of rotations about a fixed point in four-dimensional Euclidean space is denoted SO. The name comes from the fact that it is the orthogonal group of order 4. In this article rotation means rotational displacement, for the sake of uniqueness rotation angles are assumed to be in the segment except where mentioned or clearly implied by the context otherwise. A fixed plane is a plane for which every vector in the plane is unchanged after the rotation, an invariant plane is a plane for which every vector in the plane, although it may be affected by the rotation, remains in the plane after the rotation. Four-dimensional rotations are of two types, simple rotations and double rotations, a simple rotation R about a rotation centre O leaves an entire plane A through O fixed. Every plane B that is orthogonal to A intersects A in a certain point P. Each such point P is the centre of the 2D rotation induced by R in B, all these 2D rotations have the same rotation angle α. Half-lines from O in the axis-plane A are not displaced, half-lines from O orthogonal to A are displaced through α, all other half-lines are displaced through an angle < α. For each rotation R of 4-space, there is at least one pair of orthogonal 2-planes A and B each of which are invariant, hence R operating on either of these planes produces an ordinary rotation of that plane. For almost all R, the rotation angles α in plane A and β in plane B — both assumed to be nonzero — are different, the unequal rotation angles α and β satisfying -π < α, β < π are almost* uniquely determined by R. Assuming that 4-space is oriented, then the orientations of the 2-planes A and B can be consistent with this orientation in two ways. If the rotation angles are unequal, R is sometimes termed a double rotation, *Assuming that 4-space is oriented, then an orientation for each of the 2-planes A and B can be chosen to be consistent with this orientation of 4-space in two equally valid ways. If the angles from one choice of orientations of A and B are. If the rotation angles of a rotation are equal then there are infinitely many invariant planes instead of just two, and all half-lines from O are displaced through the same angle. Such rotations are called isoclinic or equiangular rotations, or Clifford displacements, beware, not all planes through O are invariant under isoclinic rotations, only planes that are spanned by a half-line and the corresponding displaced half-line are invariant. Assuming that an orientation has been chosen for 4-dimensional space. Now assume that only the rotation angle α is specified, then there are in general four isoclinic rotations in planes OUX and OYZ with rotation angle α, depending on the rotation senses in OUX and OYZ. We make the convention that the senses from OU to OX

10.
Rotation
–
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object always rotates around a line called a rotation axis. If the axis passes through the center of mass, the body is said to rotate upon itself. A rotation about a point, e. g. the Earth about the Sun, is called a revolution or orbital revolution. The axis is called a pole, mathematically, a rotation is a rigid body movement which, unlike a translation, keeps a point fixed. This definition applies to rotations within both two and three dimensions All rigid body movements are rotations, translations, or combinations of the two, a rotation is simply a progressive radial orientation to a common point. That common point lies within the axis of that motion, the axis is 90 degrees perpendicular to the plane of the motion. If the axis of the rotation lies external of the body in question then the body is said to orbit, there is no fundamental difference between a “rotation” and an “orbit” and or spin. The key distinction is simply where the axis of the rotation lies and this distinction can be demonstrated for both “rigid” and “non rigid” bodies. If a rotation around a point or axis is followed by a rotation around the same point/axis. The reverse of a rotation is also a rotation, thus, the rotations around a point/axis form a group. However, a rotation around a point or axis and a rotation around a different point/axis may result in something other than a rotation, Rotations around the x, y and z axes are called principal rotations. Rotation around any axis can be performed by taking a rotation around the x axis, followed by a rotation around the y axis and that is to say, any spatial rotation can be decomposed into a combination of principal rotations. In flight dynamics, the rotations are known as yaw, pitch. This terminology is used in computer graphics. In astronomy, rotation is an observed phenomenon. Stars, planets and similar bodies all spin around on their axes, the rotation rate of planets in the solar system was first measured by tracking visual features. Stellar rotation is measured through Doppler shift or by tracking active surface features and this rotation induces a centrifugal acceleration in the reference frame of the Earth which slightly counteracts the effect of gravity the closer one is to the equator

11.
Angular momentum
–
In physics, angular momentum is the rotational analog of linear momentum. It is an important quantity in physics because it is a conserved quantity – the angular momentum of a system remains constant unless acted on by an external torque. The definition of momentum for a point particle is a pseudovector r×p. This definition can be applied to each point in continua like solids or fluids, unlike momentum, angular momentum does depend on where the origin is chosen, since the particles position is measured from it. The angular momentum of an object can also be connected to the angular velocity ω of the object via the moment of inertia I. However, while ω always points in the direction of the rotation axis, Angular momentum is additive, the total angular momentum of a system is the vector sum of the angular momenta. For continua or fields one uses integration, torque can be defined as the rate of change of angular momentum, analogous to force. Applications include the gyrocompass, control moment gyroscope, inertial systems, reaction wheels, flying discs or Frisbees. In general, conservation does limit the motion of a system. In quantum mechanics, angular momentum is an operator with quantized eigenvalues, Angular momentum is subject to the Heisenberg uncertainty principle, meaning only one component can be measured with definite precision, the other two cannot. Also, the spin of elementary particles does not correspond to literal spinning motion, Angular momentum is a vector quantity that represents the product of a bodys rotational inertia and rotational velocity about a particular axis. Angular momentum can be considered an analog of linear momentum. Thus, where momentum is proportional to mass m and linear speed v, p = m v, angular momentum is proportional to moment of inertia I. Unlike mass, which only on amount of matter, moment of inertia is also dependent on the position of the axis of rotation. Unlike linear speed, which occurs in a line, angular speed occurs about a center of rotation. Therefore, strictly speaking, L should be referred to as the angular momentum relative to that center and this simple analysis can also apply to non-circular motion if only the component of the motion which is perpendicular to the radius vector is considered. In that case, L = r m v ⊥, where v ⊥ = v sin θ is the component of the motion. It is this definition, × to which the moment of momentum refers

12.
Absolute rotation
–
In physics, the concept of absolute rotation—rotation independent of any external reference—is a topic of debate about relativity, cosmology, and the nature of physical laws. For the concept of rotation to be scientifically meaningful, it must be measurable. In other words, can an observer distinguish between the rotation of an object and their own rotation. Newton suggested two experiments to resolve this problem, one is the effects of centrifugal force upon the shape of the surface of water rotating in a bucket. The second is the effect of force upon the tension in a string joining two spheres rotating about their center of mass. A related third example, given by Albert Einstein in the development of relativity, is a rotating elastic sphere. Like a rotating planet bulging at the equator, the sphere deforms into a squashed spheroid depending on its rotation, in general relativity no external causes are invoked. The rotation is relative to the local geodesics, and since the local geodesics eventually channel information from the distant stars, there appears to be absolute rotation relative to these stars. In theoretical physics, particularly in discussions of theories, Machs principle is the name given by Einstein to a hypothesis often credited to the physicist. The idea is that the motion of a rotating reference frame is determined by the large-scale distribution of matter in the universe. Machs principle says that there is a law that relates the motion of the distant stars to the local inertial frame. If you see all the stars whirling around you, Mach suggests that there is some physical law which would make it so you would feel a centrifugal force, the principle is often stated in vague ways, like mass out there influences inertia here. Because rotating water has a surface, if the surface you see is concave. Centrifugal force is needed to explain the concavity of the water in a frame of reference because the water appears stationary in this frame. Thus, observers looking at the water need the centrifugal force to explain why the water surface is concave. If you need a force to explain what you see. Newtons conclusion was that rotation is absolute, other thinkers suggest that pure logic implies only relative rotation makes sense. Newton also proposed another experiment to measure rate of rotation