physical science: physics
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Physical Science: Physics. Work, Power, Waves, EM Spectrum. Work and Power. Work in physics is not the same as the everyday meaning of work… Work - the product of force and distance -the transfer of energy Work is done when a force is exerted on an object and that object moves - PowerPoint PPT PresentationTRANSCRIPT
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Physical Science: Physics
Work, Power, Waves, EM Spectrum
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Work and Power
Work in physics is not the same as the everyday meaning of work…– Work- the product of force and distance -the transfer of energy
• Work is done when a force is exerted on an object and that object moves
– Work requires motion– For a force to do work on an object, some of the
force must act in the same direction as the object moves. If there is no movement, no work is done
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Work and Power
Work– Work is done when a force is exerted on an object and that
object moves• Work requires motion• For a force to do work on an object, some of the force must act
in the same direction as the object moves. If there is no movement, no work is done
– Work depends on Direction• Any part of a force that does not act in the direction of motion
does no work on an object– See figure 2-B
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Work and Power
Calculating Work– Work = Force x Distance
• Force in newtons (N)
• Distance in meters (m)
• Work in joules (J)
– Sample Problem: A weight-lifter applies force to a 1600 N barbell, to lift it over his head (a height of 2.0 m). How much work is done by the weight-lifter?
• W = F x D
F = 1600 ND = 2.0 m
W = 1600(2.0) = 3200 J
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Work and Power
Power- is the rate of doing work– Doing work at a faster rate requires more
power. To increase power, you can increase the amount of work done in a give time, or you can do a given amount of work in less time.
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Work and Power
Calculating Power– Power = Work/Time
• Work in joules (J)
• Time in seconds (s)
• Power in watts (W)– One watt is equal to one joule per second
– Sample Problem: When you lift a box, work is done (1340 J). It takes you 1.8 seconds to lift the box. How much power is done?
• P = W/t
W = 1340 Nt = 1.8 s
P = 1340/1.8 = 744.44444 ~ 740 W
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Work and Power
Sample Problem:– You exert a vertical force of 88 N to lift a
box to a height of 1.5 m in a time of 2.3 seconds. How much power is used to lift the box?
• W = FxD & P = W/t
F = 88 ND = 1.5 mW = ?t = 2.3 s
W = F x D = 88(1.5) = 132 J
P = W/t = 132/2.3 = 57.391304 ~ 57 W
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Thermal Energy and Matter
Work and Heat– Friction makes machines inefficient
• Friction causes some of the work done to be converted to thermal energy, rather than be used to do useful work
– Heat- the transfer of thermal energy from one object to another because of a temperature difference
• Heat flows spontaneously from hot objects to cold objects
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Thermal Energy and Matter
Thermal energy depends on the mass, temperature, and phase (solid, liquid, or gas) of an object.– Temperature- is a measure of how hot or
cold an object is in relation to reference point
– The more mass an object has, the more thermal energy it will have
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Thermal Energy and Matter
Thermal expansion occurs when particles of matter move farther apart as temperature increases– When objects heat up they expand, and
when objects cool down they contract
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Thermal Energy and Matter
First Law of Thermodynamics– States that energy is conserved
• If energy is added to a system, it will either increase the thermal energy of the system or do work on the system
– Ex: bike tire, air inside the tire, and air pump are the system…when you use the pump, there is a force exerted on the pump, which does work on the system (adding air to the tire) some of the work is converted to thermal energy as well
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Thermal Energy and Matter
Second Law of Thermodynamics– States that thermal energy can flow from
colder objects to hotter objects only if work is done on the system
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Thermal Energy and Matter
Third Law of Thermodynamics– States that absolute zero cannot be
reached
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Properties of Mechanical Waves
Frequency and Period– Periodic Motion- any motion that repeats at regular
intervals
– Period- the time required for one cycle, a complete motion that returns to is starting point
– Frequency- the number of complete cycles in a given time
• Any periodic motion has a frequency
• Measured in cycles per second, or hertz (Hz)
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Properties of Mechanical Waves
Frequency and Period– A wave’s
frequency equals the frequency of the vibrating source producing the wave
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www.airynothing.com/high_energy_tutorial/basics/basics02.html
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Properties of Mechanical Waves
Wavelength- the distance between a point on one wave and the same point on the next cycle of the wave
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Electromagnetic Waves
Electromagnetic Waves- transverse waves consisting of changing electric fields and changing magnetic fields– Produced and travel differently compared
to mechanical waves
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Electromagnetic Waves
How Produced?– EM waves are produced by constantly changing fields
• Electric field- in a region of space exerts electric forces on charged particles
– Produced by electric charges and by changing magnetic fields
• Magnetic field- in a region of space produces magnetic forces– Produced by magnets, changing electric fields, and by vibrating
charges
– EM waves are produced when an electric charge vibrates or accelerates
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Electromagnetic Waves
EM waves vary in wavelength and frequency– Not all EM waves are the same
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Electromagnetic Spectrum
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http://zebu.uoregon.edu/~imamura/122/images/electromagnetic-spectrum.jpg
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Electromagnetic Spectrum
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http://www.dnr.sc.gov/ael/personals/pjpb/lecture/lecture.html
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Electromagnetic Waves
Electromagnetic Spectrum- the full range of frequencies of EM radiation – Includes:
• Radio waves• Infrared rays• Visible light• Ultraviolet rays• X-rays• Gamma rays
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Electromagnetic Waves
Behavior of Light– Materials can be transparent, translucent, or opaque
• Transparent- a material that transmits light/allows most of the light that strikes it to pass through it
• Translucent- a material that scatters light– You can see through it, but the objects do not look clear or distinct
• Opaque- a material that either absorbs or reflects all of the light that strikes it