Define the following
♤ work
♤ energy
♤ displacement
and also write its SI Units....○○○○
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work : In physics, work is related to the amount of energy transferred to or from a system by a force. It is a scalar-valued quantity with SI units of joule.
energy: There are many forms of energy:
Spring energy: Work has been done on a spring to compress or stretch it; the spring has the ability to push or pull on another object and do work on it. The force required to stretch a spring is proportional to the distance it is stretched: F = kx where x is the stretch distance and k is a constant characteristic of the spring (big heavy springs have larger k values). The work done in stretching a spring from 0 to x is the integral of dW = Fdx. Since the force function is linear, we can just take the average force of kx/2 and avoid using calculus:
W = average F x distance = (kx/2)(x) = ½kx²
Assuming 100% efficiency, the energy stored in a stretched spring is the same as the work done in stretching it, so Spring E = ½kx²
Example: How much energy is stored in a spring with k = 2000 N/m that has been stretched 1 cm away from its equilibrium length?
E = ½kx² = ½(2000)(0.01)² = 0.1 J
Gravitational potential energy: a mass has been lifted to a height; when released it will be pulled down by gravity and can do work on another object as it falls.
Example: Find the energy stored in a tonne of water at the top of a 20 m high hydroelectric dam.
The long way is to use F = mg and then W = Fd to find the work needed to lift the water up.
The short way is to combine the formulas, replacing F with mg and using h (height) in place of d:
Gravitational energy = W = Fd = mgh
Egravity = mgh = (1000 kg)(9.81 m/s²)(20 m) = 196200 kg m²/s² = 1.96 x 105 J
Kinetic energy: A mass is moving and can do work when it hits another object. Ekinetic = ½mΔV2 = ½m(Vf2-Vi2)
Example: A 8kg ball is moving at 5m/s. EK = ½(8 kg)(5 m/s)2 = 100 J.
Electrical energy: Electrons can flow out of a battery or capacitor and do work on another electrical component such as a light bulb.
Photon energy: Although massless, a photon does have energy; in the amount hf where f is the photon's frequency and h is Planck's constant. This is the energy that warms your face in the morning sun and burns your unguarded nose at the beach.
Example: Red, at 400Thz has energy
Ered = hf = (6.626×10−34
J⋅s)(400×1012
hz) = 2.5e-19 J
Not much from each photon, but photons come from the sun in vast numbers; one estimate is 1017 photons per second per square centimeter.
Chemical energy: When some kinds of molecules are combined with others, energy can be released, usually as heat, light, or motion. When coal is burned it releases photon energy stored by plants millions of years before. When hydrogen combines with oxygen to form water, heat is released as well. A fire is oxygen combining with other substances; this also produces heat. Mixing mentos and coke produces foam whose mechanical properties can be exploited as in a MythBuster's Christmas machine.
Example: One stick of dynamite producesabout a Megajoule.
Nuclear energy: When an atom fissions it releases various particles and a little bit of heat. This energy was stored when the atom was created in the depths of a nova, an exploding star. Although the heat from each fission is miniscule, when the released particles trigger a cascade of fissioning atoms, the total energy can be enormous; as evidenced by the destruction wrought by an atomic weapon.
displacement : Displacement (symbolized d or s ),also called length or distance, is a one-dimensional quantity representing the separation between two definedpoints. The standard unit ofdisplacement in the International System of Units ( SI ) is the meter (m).Displacement is usually measured ordefined along a straight line.
energy: There are many forms of energy:
Spring energy: Work has been done on a spring to compress or stretch it; the spring has the ability to push or pull on another object and do work on it. The force required to stretch a spring is proportional to the distance it is stretched: F = kx where x is the stretch distance and k is a constant characteristic of the spring (big heavy springs have larger k values). The work done in stretching a spring from 0 to x is the integral of dW = Fdx. Since the force function is linear, we can just take the average force of kx/2 and avoid using calculus:
W = average F x distance = (kx/2)(x) = ½kx²
Assuming 100% efficiency, the energy stored in a stretched spring is the same as the work done in stretching it, so Spring E = ½kx²
Example: How much energy is stored in a spring with k = 2000 N/m that has been stretched 1 cm away from its equilibrium length?
E = ½kx² = ½(2000)(0.01)² = 0.1 J
Gravitational potential energy: a mass has been lifted to a height; when released it will be pulled down by gravity and can do work on another object as it falls.
Example: Find the energy stored in a tonne of water at the top of a 20 m high hydroelectric dam.
The long way is to use F = mg and then W = Fd to find the work needed to lift the water up.
The short way is to combine the formulas, replacing F with mg and using h (height) in place of d:
Gravitational energy = W = Fd = mgh
Egravity = mgh = (1000 kg)(9.81 m/s²)(20 m) = 196200 kg m²/s² = 1.96 x 105 J
Kinetic energy: A mass is moving and can do work when it hits another object. Ekinetic = ½mΔV2 = ½m(Vf2-Vi2)
Example: A 8kg ball is moving at 5m/s. EK = ½(8 kg)(5 m/s)2 = 100 J.
Electrical energy: Electrons can flow out of a battery or capacitor and do work on another electrical component such as a light bulb.
Photon energy: Although massless, a photon does have energy; in the amount hf where f is the photon's frequency and h is Planck's constant. This is the energy that warms your face in the morning sun and burns your unguarded nose at the beach.
Example: Red, at 400Thz has energy
Ered = hf = (6.626×10−34
J⋅s)(400×1012
hz) = 2.5e-19 J
Not much from each photon, but photons come from the sun in vast numbers; one estimate is 1017 photons per second per square centimeter.
Chemical energy: When some kinds of molecules are combined with others, energy can be released, usually as heat, light, or motion. When coal is burned it releases photon energy stored by plants millions of years before. When hydrogen combines with oxygen to form water, heat is released as well. A fire is oxygen combining with other substances; this also produces heat. Mixing mentos and coke produces foam whose mechanical properties can be exploited as in a MythBuster's Christmas machine.
Example: One stick of dynamite producesabout a Megajoule.
Nuclear energy: When an atom fissions it releases various particles and a little bit of heat. This energy was stored when the atom was created in the depths of a nova, an exploding star. Although the heat from each fission is miniscule, when the released particles trigger a cascade of fissioning atoms, the total energy can be enormous; as evidenced by the destruction wrought by an atomic weapon.
displacement : Displacement (symbolized d or s ),also called length or distance, is a one-dimensional quantity representing the separation between two definedpoints. The standard unit ofdisplacement in the International System of Units ( SI ) is the meter (m).Displacement is usually measured ordefined along a straight line.
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