Friction - Revision history

YorickAndeweg: /* A Mathematical Model */

2019-08-02T18:26:33Z

A Mathematical Model

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	This formula may also be written		This formula may also be written

	<math>F_s \leq \mu_s * N</math>		<math>F_s \leq \mu_s * N</math>.

	<li>Kinetic Friction</li>		<li>Kinetic Friction</li>

YorickAndeweg: /* A Mathematical Model */

2019-08-02T18:26:06Z

A Mathematical Model

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	where <math>\mu_s</math> is the coefficient of static friction of the objects and <math>N</math> is the normal force between the objects. <math>\mu_s</math> is a property of the materials of the surfaces in contact and is usually less than 1. <math>\mu_s</math> has no units because it is a ratio of one force to another.		where <math>\mu_s</math> is the coefficient of static friction of the objects and <math>N</math> is the normal force between the objects. <math>\mu_s</math> is a property of the materials of the surfaces in contact and is usually less than 1. <math>\mu_s</math> has no units because it is a ratio of one force to another.

			This formula may also be written

			<math>F_s \leq \mu_s * N</math>

	<li>Kinetic Friction</li>		<li>Kinetic Friction</li>

YorickAndeweg: /* The Main Idea */

2019-07-22T17:54:20Z

The Main Idea

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	<li>[[Static Friction]]</li>		<li>[[Static Friction]]</li>

	When two objects touch each other and there is no sliding between their surfaces of contact, they exert static friction forces on each other. The static friction force acting on each object opposes any force that would cause it to slide relative to the other object. For example, consider a heavy dresser at rest on the floor. If a child pushes against the side of the dresser in an attempt to slide it, that exerts a force on the dresser, but the ground would exert on it an equal and opposite static friction force that balances the force exerted by the child, so the dresser stays at rest. The static friction force can take on whatever direction and magnitude necessary to balance an external net force that threatens to cause sliding motion between two surfaces. However, the magnitude of the static friction force is limited by a maximum value. If the external force becomes strong enough, the static friction force can be overcome and the surfaces can begin to slide, at which point the friction between the objects becomes kinetic. For example, now consider an adult pushing against the same heavy dresser. The adult can exert a stronger force than the child, and if it exceeds the maximum possible static friction force, the dresser can be set into motion and slid across the floor. Note that static friction is present between rolling objects and the surface on which they roll. For more information, see the "Static Friction on Rolling Objects" section on the [[Static Friction]] page as well as the [[Rolling Motion]] page.		When two objects touch each other and there is no sliding between their surfaces of contact, they exert static friction forces on each other. The static friction force acting on each object opposes any force that would cause it to slide relative to the other object. For example, consider a heavy dresser at rest on the floor. If a child pushes against the side of the dresser in an attempt to slide it, that exerts a force on the dresser, but the ground would exert on it an equal and opposite static friction force that balances the force exerted by the child, so the dresser stays at rest. The static friction force can take on whatever direction and magnitude necessary to balance an external net force that threatens to cause sliding motion between two surfaces. However, the magnitude of the static friction force is limited by a maximum value. If the external force becomes strong enough, the static friction force can be overcome and the surfaces can begin to slide, at which point the friction between the objects becomes kinetic. For example, now consider an adult pushing against the same heavy dresser. The adult can exert a stronger force than the child, and if it exceeds the maximum possible static friction force, the dresser can be set into motion and slid across the floor. Note that static friction is present between rolling objects and the surface on which they roll. For more information, see the "Static Friction on Rolling Objects" section on the [[Static Friction]] page, as well as the [[Rolling Motion]] page.

	<li>[[Kinetic Friction]]</li>		<li>[[Kinetic Friction]]</li>

YorickAndeweg: /* The Main Idea */

2019-07-22T17:54:09Z

The Main Idea

← Older revision		Revision as of 13:54, 22 July 2019
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	<li>[[Static Friction]]</li>		<li>[[Static Friction]]</li>

	When two objects touch each other and there is no sliding between their surfaces of contact, they exert static friction forces on each other. The static friction force acting on each object opposes any force that would cause it to slide relative to the other object. For example, consider a heavy dresser at rest on the floor. If a child pushes against the side of the dresser in an attempt to slide it, that exerts a force on the dresser, but the ground would exert on it an equal and opposite static friction force that balances the force exerted by the child, so the dresser stays at rest. The static friction force can take on whatever direction and magnitude necessary to balance an external net force that threatens to cause sliding motion between two surfaces. However, the magnitude of the static friction force is limited by a maximum value. If the external force becomes strong enough, the static friction force can be overcome and the surfaces can begin to slide, at which point the friction between the objects becomes kinetic. For example, now consider an adult pushing against the same heavy dresser. The adult can exert a stronger force than the child, and if it exceeds the maximum possible static friction force, the dresser can be set into motion and slid across the floor. Note that static friction is present between rolling objects and the surface on which they roll. For more information, see the "Static Friction on Rolling Objects" section on the [[Static Friction]] page ~~and~~ the [[Rolling Motion]] page.		When two objects touch each other and there is no sliding between their surfaces of contact, they exert static friction forces on each other. The static friction force acting on each object opposes any force that would cause it to slide relative to the other object. For example, consider a heavy dresser at rest on the floor. If a child pushes against the side of the dresser in an attempt to slide it, that exerts a force on the dresser, but the ground would exert on it an equal and opposite static friction force that balances the force exerted by the child, so the dresser stays at rest. The static friction force can take on whatever direction and magnitude necessary to balance an external net force that threatens to cause sliding motion between two surfaces. However, the magnitude of the static friction force is limited by a maximum value. If the external force becomes strong enough, the static friction force can be overcome and the surfaces can begin to slide, at which point the friction between the objects becomes kinetic. For example, now consider an adult pushing against the same heavy dresser. The adult can exert a stronger force than the child, and if it exceeds the maximum possible static friction force, the dresser can be set into motion and slid across the floor. Note that static friction is present between rolling objects and the surface on which they roll. For more information, see the "Static Friction on Rolling Objects" section on the [[Static Friction]] page as well as the [[Rolling Motion]] page.

	<li>[[Kinetic Friction]]</li>		<li>[[Kinetic Friction]]</li>

YorickAndeweg: /* The Main Idea */

2019-07-09T16:20:39Z

The Main Idea

← Older revision		Revision as of 12:20, 9 July 2019
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	<li>[[Static Friction]]</li>		<li>[[Static Friction]]</li>

	When two objects touch each other and there is no sliding between their surfaces of contact, they exert static friction forces on each other. The static friction force acting on each object opposes any force that would cause it to slide relative to the other object. For example, consider a heavy dresser at rest on the floor. If a child pushes against the side of the dresser in an attempt to slide it, that exerts a force on the dresser, but the ground would exert on it an equal and opposite static friction force that balances the force exerted by the child, so the dresser stays at rest. The static friction force can take on whatever direction and magnitude necessary to balance an external net force that threatens to cause sliding motion between two surfaces. However, the magnitude of the static friction force is limited by a maximum value. If the external force becomes strong enough, the static friction force can be overcome and the surfaces can begin to slide, at which point the friction between the objects becomes kinetic. For example, now consider an adult pushing against the same heavy dresser. The adult can exert a stronger force than the child, and if it exceeds the maximum possible static friction force, the dresser can be set into motion and slid across the floor. Note that static friction is present between rolling objects and the surface on which they roll. For more information, see the "~~rolling friction~~" section on the [[Static Friction]] page.		When two objects touch each other and there is no sliding between their surfaces of contact, they exert static friction forces on each other. The static friction force acting on each object opposes any force that would cause it to slide relative to the other object. For example, consider a heavy dresser at rest on the floor. If a child pushes against the side of the dresser in an attempt to slide it, that exerts a force on the dresser, but the ground would exert on it an equal and opposite static friction force that balances the force exerted by the child, so the dresser stays at rest. The static friction force can take on whatever direction and magnitude necessary to balance an external net force that threatens to cause sliding motion between two surfaces. However, the magnitude of the static friction force is limited by a maximum value. If the external force becomes strong enough, the static friction force can be overcome and the surfaces can begin to slide, at which point the friction between the objects becomes kinetic. For example, now consider an adult pushing against the same heavy dresser. The adult can exert a stronger force than the child, and if it exceeds the maximum possible static friction force, the dresser can be set into motion and slid across the floor. Note that static friction is present between rolling objects and the surface on which they roll. For more information, see the "Static Friction on Rolling Objects" section on the [[Static Friction]] page and the [[Rolling Motion]] page.

	<li>[[Kinetic Friction]]</li>		<li>[[Kinetic Friction]]</li>

YorickAndeweg: /* External links */

2019-07-06T19:59:32Z

External links

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	===External links===		===External links===

	*~~Hyper Physics:~~ http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#fri		*[http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#fri Hyperphysics page on friction]
	*~~PHET Simulation:~~ https://phet.colorado.edu/en/simulation/friction		*[https://phet.colorado.edu/en/simulation/friction PHET simulation]
			*[https://en.wikipedia.org/wiki/Friction#Static_friction Wikipedia page on friction]
			*[http://www.animations.physics.unsw.edu.au/jw/weight_and_friction.htm A couple of animations]

	==References==		==References==

YorickAndeweg: /* See also */

2019-07-06T19:57:33Z

YorickAndeweg: /* Connectedness */

2019-07-06T19:55:06Z

Connectedness

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	==Connectedness==		==Connectedness==

	Friction has countless applications in industry and everyday life. In some scenarios, such as in engines and motors, it is undesirable, as it dissipates power that would otherwise be delivered to a useful task. In these cases, it is important to understand friction so that it can be minimized and factored into calculations. In other scenarios, such as on the brakes of a car, friction is desirable and necessary, and it is important to understand friction so that it can be maximized and calculated. In addition to affecting motion, friction raises temperatures, can wear down objects, and can emit sound, which may also need to be taken into account, depending on the application. There are many, many situations and technologies where friction plays a critical role. Here are a few examples.		Friction has countless applications in industry and everyday life. In some scenarios, such as in engines and motors, it is undesirable, as it dissipates power that would otherwise be delivered to a useful task. In these cases, it is important to understand friction so that it can be minimized and factored into calculations. In other scenarios, such as on the brakes of a car, friction is desirable and necessary, and it is important to understand friction so that it can be maximized and calculated. In addition to affecting motion, kinetic friction raises temperatures, can wear down objects, and can emit sound, which may also need to be taken into account, depending on the application. There are many, many situations and technologies where friction plays a critical role. Here are a few examples.

	===Wheels===		===Wheels===

YorickAndeweg: /* A Mathematical Model */

2019-07-06T19:45:26Z

A Mathematical Model

← Older revision		Revision as of 15:45, 6 July 2019
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	<math>F_k = \mu_k * N</math>		<math>F_k = \mu_k * N</math>

	where <math>\mu_k</math> is the coefficient of kinetic friction of the objects and <math>N</math> is the normal force between the objects. <math>\mu_k</math> is a property of the materials of the surfaces in contact and is usually less than 1. <math>\mu_k</math> has no units because it is a ratio of one force to another.		where <math>\mu_k</math> is the coefficient of kinetic friction of the objects and <math>N</math> is the normal force between the objects. <math>\mu_k</math> is a property of the materials of the surfaces in contact and is usually less than 1. <math>\mu_k</math> has no units because it is a ratio of one force to another. For any given pair of surfaces, their <math>\mu_s</math> value is greater than their <math>\mu_k</math> value.

	Note that this formula indicates that the magnitude of the kinetic friction force does not depend on the speed of the sliding between the objects.		Note that this formula indicates that the magnitude of the kinetic friction force does not depend on the speed of the sliding between the objects.

	~~For any given pair of surfaces, their <math>\mu_s</math> value is greater than their <math>\mu_k</math> value.~~

	<li>Fluid Friction</li>		<li>Fluid Friction</li>

YorickAndeweg: /* History */

2019-07-06T19:37:48Z

History

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	==History==		==History==

	Evidence of human knowledge of friction is very old. Tools intended to start fires by friction have been dated to at least 50,000 BC, and wheels are estimated to have been invented in 8,000 BC in Asia. Ancient Egyptian art from about 2,000 BC depicts the use of lubricants under sledges used to transport large objects and in the axles of chariots. The Greek philosopher Themistius (390-320 BC) is widely considered the first individual to make an explicit observation about friction: he stated that static friction is greater than sliding (kinetic) friction. Leonardo Da Vinci (1452-1519) also studied friction. He observed that rougher materials experience more friction, that the friction force between two objects was proportional to the normal force between them, and that the friction force between two objects did not depend on their area of contact. Unfortunately, he made these observations in one of his many notebooks without publishing them, and no one recognized the importance ~~of these observations regarding friction~~ until after ~~they~~ had been independently rediscovered by Guillaume Amontons (1663-1705). Amontons published his discoveries in 1699. In addition to what had already been observed by Da Vinci, Amontons added that the kinetic friction force is independent of the sliding speed, and speculated about the causes of friction. Isaac Newton (1642-1727) was the first to describe fluid friction in his work titled Principia Mathematica in 1687. Charles-Augustin Coulomb (1736-1806) performed many experiments supporting earlier discoveries and stated that the friction experienced by a load on wheels is inversely proportional to the radius of the wheels. F. Philip Bowden and David Tabor wrote in 1950 that friction was largely the result of adhesive forces between surfaces. These adhesive forces were proportional to the number and size of contact points between the surfaces, which were in turn proportional to the normal force between them. This is believed to be the cause for friction today.		Evidence of human knowledge of friction is very old. Tools intended to start fires by friction have been dated to at least 50,000 BC, and wheels are estimated to have been invented in 8,000 BC in Asia. Ancient Egyptian art from about 2,000 BC depicts the use of lubricants under sledges used to transport large objects and in the axles of chariots. The Greek philosopher Themistius (390-320 BC) is widely considered the first individual to make an explicit observation about friction: he stated that static friction is greater than sliding (kinetic) friction. Leonardo Da Vinci (1452-1519) also studied friction. He observed that rougher materials experience more friction, that the friction force between two objects was proportional to the normal force between them, and that the friction force between two objects did not depend on their area of contact. Unfortunately, he made these observations in one of his many notebooks without publishing them, and no one recognized the notes' importance until after the observations had been independently rediscovered by Guillaume Amontons (1663-1705). Amontons published his discoveries in 1699. In addition to what had already been observed by Da Vinci, Amontons added that the kinetic friction force is independent of the sliding speed, and speculated about the causes of friction. Isaac Newton (1642-1727) was the first to describe fluid friction in his work titled Principia Mathematica in 1687. Charles-Augustin Coulomb (1736-1806) performed many experiments supporting earlier discoveries and stated that the friction experienced by a load on wheels is inversely proportional to the radius of the wheels. F. Philip Bowden and David Tabor wrote in 1950 that friction was largely the result of adhesive forces between surfaces. These adhesive forces were proportional to the number and size of contact points between the surfaces, which were in turn proportional to the normal force between them. This is believed to be the cause for friction today.

	== See also ==		== See also ==

← Older revision		Revision as of 15:57, 6 July 2019
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	*[[Air Resistance]]		*[[Air Resistance]]
	*[[Terminal Velocity and Friction Due to Air]]		*[[Terminal Velocity and Friction Due to Air]]
			*[[Rolling Motion]]

	===External links===		===External links===