| DivergingLensParallelRay |
For a diverging lens, the parallel ray originates at the object, travels parallel to the lens axis, passes through the lens, and changes direction to appear to originate from the front focus. |
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| DivergingMirrorFocalRay |
For a diverging mirror, the focal ray originates at the object, travels toward the back focus, is reflected, and travels parallel to the mirror axis. |
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| DivergingMirrorParallelRay |
For a diverging mirror, the parallel ray originates at the object, travels parallel to the mirror axis, is reflected, and changes direction to appear to originate from the back focus. |
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| Duration |
A duration is the magnitude of a time interval or time period. The SI unit of duration is the second, $\mathrm{s}$. |
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| EarthMass |
Earth's mass is approximately $5.97 \times 10^{24}$ kg. |
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| EarthRadius |
Earth's radius is approximately $6.4 \times 10^{6}$ m. |
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| EarthSunDistance |
The distance from Earth to the Sun is approximately $1.5 \times 10^{8}$ km. |
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| EarthSurfaceGravAccel |
Near Earth's surface, the magnitude of the gravitational acceleration, $g$, is approximately $9.8 \, \mathrm{m/s}^2$. |
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| EarthSurfaceGravDir |
Over a sufficiently small area of Earth's surface, the direction of Earth's gravitational acceleration can be approximated as constant, and defines "down". |
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| EarthSurfaceGravForceMag |
Near Earth's surface, the magnitude of Earth's gravitational force on an object is $F_\text{g}=m g$, where $m$ is the mass of the object, in kilograms, and $g=9.8 \, \mathrm{m/s}^2$. |
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| ElectricCharge |
Electric charge is a property of some particles. There are two types of electric charge, positive and negative. A particle with no charge is neutral. |
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| ElectronCharge |
The electron charge is $-e$, where $e$ is the elementary charge unit. |
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| ElectronMass |
The electron mass, $m_\text{e}$, is $9.11 \times 10^{-31} \, \mathrm{kg}$. |
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| ElectrostaticDirection |
The direction of the electrostatic force of object A on object B is along the line between the two objects. The direction is toward object A if the objects have charges of opposite sign and away from object A if the objects have charges of the same sign. |
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| ElectrostaticEquation |
The magnitude of the electrostatic force of object A on object B is $F_\text{AB}=k \frac{q_\text{A} q_\text{B}}{d^2}$, where $q_\text{A}$ and $q_\text{B}$ are the charges of objects A and B, in coulombs (C), respectively, $d$ is the distance between the two charges in meters (m), and the constant $k=9.0 \times 10^{9} \, \mathrm{N \cdot m}^2/\mathrm{C}^2$. |
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| ElectrostaticStrengthCharge |
The magnitude of the electrostatic force of one object on another object is proportional to the charge of each of the objects. |
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| ElectrostaticStrengthDistance |
The magnitude of the electrostatic force between two objects is proportional to the inverse square of the distance between the objects. |
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| ElementaryCharge |
The elementary charge, $e$, is the charge on a proton. Its magnitude is $1.602 \times 10^{-19} \, \mathrm{C}$. |
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| EnergyConserved |
Energy is conserved. |
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| Evidence |
Evidence is data that have been represented, analyzed, and interpreted in the context of a specific scientific question. |
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| Factorial |
The factorial of a number $n$, $n!$, is $n \times (n-1) \times (n-2) \times \ldots \times 2 \times 1$. |
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| FluidResistance |
Fluid resistance is the force exerted on an object by a fluid because of the object is moving through the fluid. |
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| FluidResistanceDirection |
The direction of the force of fluid resistance on an object is opposite to the object's motion through the fluid. |
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| FluidResistanceStrength |
The strength of the force of fluid resistance on an object is often modeled as $F=C v^x$ where $C$ is a constant that depends on the object and the fluid, $v$ is the speed of the object relative to the fluid, and the value of $x$ is usually 1, 2, or some number in between. |
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| FocalLength |
An optical element's focal length is the distance from the center of the element to the focus. For a converging(diverging) element the distance is defined to be positive(negative). |
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| Focus |
An optical element's focus is the point that incoming paraxial light rays converge to or seem to diverge from. |
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| Force |
A force is a push or a pull exerted by one entity (object) on another entity (object). |
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| ForceChangesVelocity |
A single or unbalanced force acting on an object changes the object's velocity. |
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| ForceStartObject |
If a single or unbalanced force acts on a stopped object, the object will start to move, and the motion will be in the direction of the force. |
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| ForceStrengthDirection |
A force is described by two characteristics: its strength and its direction. |
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| ForcesVectors |
Forces are vectors. |
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| ForceUnit |
The SI unit for force is the newton, N. A force of magnitude 1 N imparts an acceleration of $1 \, \mathrm{m/s}^2$ to an object of mass 1 kg. $1 \, \mathrm{N} = 1 \, \mathrm{kg \cdot m/s}^2$. |
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| ForceVelOppDir |
A force acting on an object, in the direction opposite to the object's velocity, decreases the object's speed. |
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| ForceVelPerpendicular |
A force acting on an object, in a direction perpendicular to the object's velocity, changes the object's direction but not its speed. |
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| ForceVelSameDir |
A force acting on an object, in the same direction as the object's velocity, increases the object's speed. |
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| GPEEqnUnits |
The equation for gravitational potential energy relative to a reference point is $\text{GPE}=m g h$, where $\text{GPE}$ is the object's gravitational potential energy, in joules, $m$ is the object's mass, in kilograms, $g$ is the acceleration due to gravity, in meters per second squared, and $h$ is the object's height above the reference point, in meters. |
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| GravitationalPotentialEnergy |
Gravitational potential energy is the energy that an object has because of its position in a gravitational field. |
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| GravityDirection |
The direction of the gravitational force exerted on object 1 by object 2 is towards object 2. |
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| GravityEquation |
The magnitude of the gravitational force $F_\text{g}$ of object A on object B is $F_\text{g}=G \frac{m_\text{A} m_\text{B}}{d^2}$ where $G = 6.67 \times 10^{-11} \, \mathrm{N \cdot m}^2/\mathrm{kg}^2$ is the universal gravitational constant, $m_\text{A}$ and $m_\text{B}$ are the masses of the two objects, in kilograms and $d$ is the distance between them, in meters. |
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| GravityExists |
A gravitational interaction exists between any two objects having mass. |
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| GravitySpherePoint |
The gravitational force exerted by an extended, spherically-symmetric object is identical to the force exerted by a point particle, of the same mass, located at the center of the object. |
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| GravityStrengthDistance |
The strength of the gravitational force of one object on another object is proportional to the inverse square of the distance between the objects. |
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| GravityStrengthMass |
The strength of the gravitational force of one object on another object is directly proportional to the mass of each of the objects. |
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| GravityWeak |
The force of gravity is so weak that unless at least one of the objects is very large, it can be ignored. |
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| GreaterDurationGreaterVelChange |
Given equal net forces exerted on two objects having equal masses, the object experiencing the net force for the greater duration will have the greater change of velocity. |
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| GreaterForceGreaterVelChange |
Given net forces exerted for the same duration on two objects having equal masses, the object experiencing the greater net force will have a greater change in velocity. |
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| GreaterMassLesserVelChange |
Given equal net forces acting on two objects for the same duration, the less-massive object will experience the greater change of velocity. |
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| GreaterSpeedGreaterDist |
In equal time intervals, an object with a greater speed will travel a greater distance than an object with a lesser speed. |
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| HookesLawSpring |
A Hooke's Law spring is a spring for which the restoring force is linearly proportional to, and in the opposite direction from, the displacement from its equilibrium position, i.e. $F =-k \Delta x$, where $F$ is the restoring force, in newtons, $k$ is the spring constant, in newtons per meter, and $\Delta x=\left(x-x_0\right)$ is the displacement, in meters, from the spring's current extension, $x$, to its equilibrium extension, $x_0$. |
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| Hypothesis |
A hypothesis is a type of testable explanation (model) of natural systems or phenomena, or of evidence from an investigation. |
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