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Physical Science: Physics Work, Power, Waves, EM Spectrum

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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 Presentation

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Page 1: Physical Science: Physics

Physical Science: Physics

Work, Power, Waves, EM Spectrum

Page 2: Physical Science: Physics

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

Page 3: Physical Science: Physics

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

Page 4: Physical Science: Physics

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

Page 5: Physical Science: Physics

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.

Page 6: Physical Science: Physics

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

Page 7: Physical Science: Physics

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

Page 8: Physical Science: Physics

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

Page 9: Physical Science: Physics

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

Page 10: Physical Science: Physics

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

Page 11: Physical Science: Physics

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

Page 12: Physical Science: Physics

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

Page 13: Physical Science: Physics

Thermal Energy and Matter

Third Law of Thermodynamics– States that absolute zero cannot be

reached

Page 14: Physical Science: Physics

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)

Page 15: Physical Science: Physics

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

Page 16: Physical Science: Physics

Properties of Mechanical Waves

Wavelength- the distance between a point on one wave and the same point on the next cycle of the wave

Page 17: Physical Science: Physics

Electromagnetic Waves

Electromagnetic Waves- transverse waves consisting of changing electric fields and changing magnetic fields– Produced and travel differently compared

to mechanical waves

Page 18: Physical Science: Physics

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

Page 19: Physical Science: Physics

Electromagnetic Waves

EM waves vary in wavelength and frequency– Not all EM waves are the same

Page 20: Physical Science: Physics

Electromagnetic Spectrum

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http://zebu.uoregon.edu/~imamura/122/images/electromagnetic-spectrum.jpg

Page 21: Physical Science: Physics

Electromagnetic Spectrum

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are needed to see this picture.

http://www.dnr.sc.gov/ael/personals/pjpb/lecture/lecture.html

Page 22: Physical Science: Physics

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

Page 23: Physical Science: Physics

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