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34-431: Mechanically, a seesaw is a lever which consists of a beam and fulcrum with the effort and load on either side. The most common playground design of seesaw features a board balanced in the center. A person sits on each end, and they take turns pushing their feet against the ground to lift their side into the air. Playground seesaws usually have handles for the riders to grip as they sit facing each other. One problem with

68-638: A ( F A ⋅ e A ⊥ ) − b ( F B ⋅ e B ⊥ ) = a F A − b F B , {\displaystyle F_{\theta }=\mathbf {F} _{A}\cdot {\frac {\partial \mathbf {v} _{A}}{\partial {\dot {\theta }}}}-\mathbf {F} _{B}\cdot {\frac {\partial \mathbf {v} _{B}}{\partial {\dot {\theta }}}}=a(\mathbf {F} _{A}\cdot \mathbf {e} _{A}^{\perp })-b(\mathbf {F} _{B}\cdot \mathbf {e} _{B}^{\perp })=aF_{A}-bF_{B},} where F A and F B are components of

102-426: A b . {\displaystyle MA={\frac {F_{2}}{F_{1}}}={\frac {a}{b}}.\!} This relationship shows that the mechanical advantage can be computed from ratio of the distances from the fulcrum to where the input and output forces are applied to the lever, assuming a weightless lever and no losses due to friction, flexibility or wear. This remains true even though the "horizontal" distance (perpendicular to

136-403: A b . {\displaystyle MA={\frac {F_{B}}{F_{A}}}={\frac {a}{b}}.} This is the law of the lever , which was proven by Archimedes using geometric reasoning. It shows that if the distance a from the fulcrum to where the input force is applied (point A ) is greater than the distance b from fulcrum to where the output force is applied (point B ), then the lever amplifies

170-406: A and b are distances from the fulcrum to points A and B and the force F A applied to A is the input and the force F B applied at B is the output, the ratio of the velocities of points A and B is given by a/b , so we have the ratio of the output force to the input force, or mechanical advantage, is given by: M A = F B F A =

204-401: A fixed point. The lever operates by applying forces at different distances from the fulcrum, or a pivot. As the lever rotates around the fulcrum, points further from this pivot move faster than points closer to the pivot. Therefore, a force applied to a point further from the pivot must be less than the force located at a point closer in, because power is the product of force and velocity. If

238-591: A word or syllable is doubled, often with a different vowel. Reduplication is typical of words that indicate repeated activity, such as riding up and down on a seesaw. In the southeastern New England region of the United States, it is sometimes referred to as a tilt or a tilting board . According to Michael Drout , "There are almost no 'Teeter-' forms in Pennsylvania , and if you go to western West Virginia and down into western North Carolina there

272-522: Is a band of 'Ridey-Horse' that heads almost straight south. This pattern suggests a New England term that spread down the coast and a separate, Scots-Irish development in Appalachia. 'Hickey-horse' in the coastal regions of North Carolina is consistent with other linguistic and ethnic variations." In the early 2000s, seesaws were removed from many playgrounds in the United States, citing safety concerns. However, some people have questioned whether or not

306-567: Is a direct Anglicisation of the French ci-ça , meaning literally, this-that , seemingly attributable to the back-and-forth motion for which a seesaw is known. The term may also be attributable to the repetitive motion of a saw. It may have its origins in a combination of "scie" – the French word for "saw" with the Anglo-Saxon term "saw". Thus "scie-saw" became "see-saw". Another possibility

340-451: Is evident from the recesses in the large blocks and the handling bosses which could not be used for any purpose other than for levers. The earliest remaining writings regarding levers date from the 3rd century BC and were provided, by common belief, by the Greek mathematician Archimedes , who famously stated "Give me a lever long enough and a fulcrum on which to place it, and I shall move

374-415: Is lessened. T 1 = F 1 a , T 2 = F 2 b {\displaystyle {\begin{aligned}T_{1}&=F_{1}a,\quad \\T_{2}&=F_{2}b\!\end{aligned}}} where F 1 is the input force to the lever and F 2 is the output force. The distances a and b are the perpendicular distances between

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408-482: Is one of the six simple machines identified by Renaissance scientists. A lever amplifies an input force to provide a greater output force, which is said to provide leverage , which is mechanical advantage gained in the system, equal to the ratio of the output force to the input force. As such, the lever is a mechanical advantage device , trading off force against movement. The word "lever" entered English around AD 1300 from Old French : levier . This sprang from

442-405: Is operated by applying an input force F A at a point A located by the coordinate vector r A on the bar. The lever then exerts an output force F B at the point B located by r B . The rotation of the lever about the fulcrum P is defined by the rotation angle θ in radians. Let the coordinate vector of the point P that defines the fulcrum be r P , and introduce

476-481: Is the generalized coordinate that defines the configuration of the lever, and the generalized force associated with this coordinate is given by F θ = F A ⋅ ∂ v A ∂ θ ˙ − F B ⋅ ∂ v B ∂ θ ˙ =

510-412: Is the situation of the apparent appearance, disappearance, and re-emergence of the person, seated opposite one's position, as they, seemingly, "rise" and "fall", against a changing, oscillating background - therefore: "I see you", followed by, "I saw you". In the northern inland and westernmost region of the United States, a seesaw is also called a "teeter-totter." According to linguist Peter Trudgill ,

544-447: The ancient Near East c.  5000 BC , when it was first used in a simple balance scale . In ancient Egypt c.  4400 BC , a foot pedal was used for the earliest horizontal frame loom . In Mesopotamia (modern Iraq) c.  3000 BC , the shadouf , a crane-like device that uses a lever mechanism, was invented. In ancient Egypt , workmen used the lever to move and uplift obelisks weighing more than 100 tons. This

578-579: The eagerness of children to play with them, are sometimes used to aid in mechanical processes. For example, at the Gaviotas community in Colombia , a children's seesaw is connected to a water pump . In 2019, a set of seesaws were installed spanning the US-Mexico border fence between El Paso and Ciudad Juárez. Seesaws go by several different names around the world. Seesaw , or its variant see-saw ,

612-442: The forces and the fulcrum. Since the moments of torque must be balanced, T 1 = T 2 {\displaystyle T_{1}=T_{2}\!} . So, F 1 a = F 2 b {\displaystyle F_{1}a=F_{2}b\!} . The mechanical advantage of a lever is the ratio of output force to input force. M A = F 2 F 1 =

646-400: The forces that are perpendicular to the radial segments PA and PB . The principle of virtual work states that at equilibrium the generalized force is zero, that is F θ = a F A − b F B = 0. {\displaystyle F_{\theta }=aF_{A}-bF_{B}=0.\,\!} Thus, the ratio of the output force F B to

680-426: The input force F A is obtained as M A = F B F A = a b , {\displaystyle MA={\frac {F_{B}}{F_{A}}}={\frac {a}{b}},} which is the mechanical advantage of the lever. This equation shows that if the distance a from the fulcrum to the point A where the input force is applied is greater than the distance b from fulcrum to

714-419: The input force. On the other hand, if the distance a from the fulcrum to the input force is less than the distance b from the fulcrum to the output force, then the lever reduces the input force. The use of velocity in the static analysis of a lever is an application of the principle of virtual work . A lever is modeled as a rigid bar connected to a ground frame by a hinged joint called a fulcrum. The lever

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748-442: The lengths a = | r A − r P | , b = | r B − r P | , {\displaystyle a=|\mathbf {r} _{A}-\mathbf {r} _{P}|,\quad b=|\mathbf {r} _{B}-\mathbf {r} _{P}|,} which are the distances from the fulcrum to the input point A and to the output point B , respectively. Now introduce

782-405: The lever equals the power out, and the ratio of output to input force is given by the ratio of the distances from the fulcrum to the points of application of these forces. This is known as the law of the lever . The mechanical advantage of a lever can be determined by considering the balance of moments or torque , T , about the fulcrum. If the distance traveled is greater, then the output force

816-414: The next, and thus the applied force is transferred from one lever to the next. Examples of compound levers include scales, nail clippers and piano keys. The malleus , incus and stapes are small bones in the middle ear , connected as compound levers, that transfer sound waves from the eardrum to the oval window of the cochlea . The lever is a movable bar that pivots on a fulcrum attached to

850-502: The point B where the output force is applied, then the lever amplifies the input force. If the opposite is true that the distance from the fulcrum to the input point A is less than from the fulcrum to the output point B , then the lever reduces the magnitude of the input force. Mechanical advantage Too Many Requests If you report this error to the Wikimedia System Administrators, please include

884-562: The points A and B are obtained as v A = θ ˙ a e A ⊥ , v B = θ ˙ b e B ⊥ , {\displaystyle \mathbf {v} _{A}={\dot {\theta }}a\mathbf {e} _{A}^{\perp },\quad \mathbf {v} _{B}={\dot {\theta }}b\mathbf {e} _{B}^{\perp },} where e A and e B are unit vectors perpendicular to e A and e B , respectively. The angle θ

918-411: The pull of gravity) of both a and b change (diminish) as the lever changes to any position away from the horizontal. Levers are classified by the relative positions of the fulcrum, effort and resistance (or load). It is common to call the input force "effort" and the output force "load" or "resistance". This allows the identification of three classes of levers by the relative locations of the fulcrum,

952-424: The resistance and the effort: These cases are described by the mnemonic fre 123 where the f fulcrum is between r and e for the 1st class lever, the r resistance is between f and e for the 2nd class lever, and the e effort is between f and r for the 3rd class lever. A compound lever comprises several levers acting in series: the resistance from one lever in a system of levers acts as effort for

986-420: The seesaw's design is that if a child allows himself/herself to hit the ground suddenly after jumping, or exits the seesaw at the bottom, the other child may fall and be injured. For this reason, seesaws are often mounted above a soft surface such as foam, wood chips, or sand. Seesaws are also manufactured in shapes designed to look like other things, such as airplanes , helicopters , and animals. Seesaws, and

1020-422: The seesaws should have been removed, indicating the fun provided by seesaws may outweigh the safety risk posed using them. Lever A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge , or fulcrum . A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is divided into three types . It

1054-550: The stem of the verb lever , meaning "to raise". The verb, in turn, goes back to Latin : levare , itself from the adjective levis , meaning "light" (as in "not heavy"). The word's primary origin is the Proto-Indo-European stem legwh- , meaning "light", "easy" or "nimble", among other things. The PIE stem also gave rise to the English word "light". The earliest evidence of the lever mechanism dates back to

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1088-478: The term originates from the Norfolk dialect word tittermatorter . A "teeter-totter" may also refer to a two-person swing on a swing seat , on which two children sit facing each other and the teeter-totter swings back and forth in a pendulum motion. Both teeter-totter (from teeter , as in to teeter on the edge ) and seesaw (from the verb saw ) demonstrate the linguistic process called reduplication , where

1122-448: The unit vectors e A and e B from the fulcrum to the point A and B , so r A − r P = a e A , r B − r P = b e B . {\displaystyle \mathbf {r} _{A}-\mathbf {r} _{P}=a\mathbf {e} _{A},\quad \mathbf {r} _{B}-\mathbf {r} _{P}=b\mathbf {e} _{B}.} The velocity of

1156-404: The world." Autumn Stanley argues that the digging stick can be considered the first lever, which would position prehistoric women as the inventors of lever technology. A lever is a beam connected to ground by a hinge, or pivot, called a fulcrum. The ideal lever does not dissipate or store energy, which means there is no friction in the hinge or bending in the beam. In this case, the power into

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