Physical Science: Physics

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

2. 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

3. 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

4. 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 N D = 2.0 m W = 1600(2.0) = 3200 J

5. 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.

6. 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 P = 1340/1.8 = 744.44444 ~ 740 W W = 1340 N t = 1.8 s

7. 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 P = W/t = 132/2.3 = 57.391304 ~ 57 W F = 88 N D = 1.5 m W = ? t = 2.3 s W = F x D = 88(1.5) = 132 J

8. 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

9. 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

10. 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

11. 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

12. 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

13. Thermal Energy and Matter • Third Law of Thermodynamics • States that absolute zero cannot be reached

14. 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)

15. Properties of Mechanical Waves • Frequency and Period • A wave’s frequency equals the frequency of the vibrating source producing the wave www.airynothing.com/high_energy_tutorial/basics/basics02.html

16. Properties of Mechanical Waves • Wavelength- the distance between a point on one wave and the same point on the next cycle of the wave

17. Electromagnetic Waves • Electromagnetic Waves- transverse waves consisting of changing electric fields and changing magnetic fields • Produced and travel differently compared to mechanical waves

18. 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

19. Electromagnetic Waves • EM waves vary in wavelength and frequency • Not all EM waves are the same

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

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

22. 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

23. 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