Heat and Waves

1. Heat and Waves Chapter 10 and 12 Review

2. Agenda: Waves Hooke’s Law Amplitude, period and frequency Types of waves Wave speed Interference Standing waves Heat • Temperature, measuring temperature, and thermal equilibriium • Heat transfer is energy transfer • Specific heat and calorimetry • Latent heat • Heat transfer

3. Temperature • Temperature measures the average kinetic energy of the atoms or molecules of a substance. • Temperature changes when energy is added or removed. • All objects attempt to attain thermal equilibrium by exchanging energy.

4. Temperature Continued • Matter expands as temperature increases. This is called thermal expansion. • Temperature is measured in (see your formula sheet for coversions): • degrees Fahrenheit • degrees Celsius • Kelvin

5. Heat • Thermal energy is the measure of the TOTAL kinetic energy of the molecules of a substance • Heat is the transfer of energy between substances. • Substances at different temperatures will transfer energy until they are equal. • Like all energy, heat can be measured in Joules.

6. Heat and Work • Any energy change that cannot be accounted for by a change in potential or kinetic energy can be attributed to heat (internal energy) by way of friction.

7. Specific Heat • Different materials require different amounts of energy to change their temperatures. • The energy required to raise the temperature of 1 kilogram of a substance by 1 degree Celsius is its specific heat capacity.

8. Calorimetry • Specific heat capacity of substances can be determined by calorimetry. • The amount of energy gained by the water must equal the amount of energy lost by the substance.

9. Energy during Phase Change • It takes energy to change phases. TEMPERATURE DOES NOT CHANGE DURING PHASE CHANGE. • Latent heat is the energy required to change phase. • Problem solving: when determining the energy required to change a substance from one temperature to another, you must consider if there is a phase change or not.

10. Heat Transfer • Conduction: heat transfer by direct contact between molecules • Conductors allow the flow of heat easily • Insulators inhibit the flow of heat. • Convection: heat transfer through a fluid • Radiation: energy transfer through electromagnetic waves.

11. Vibration and Waves: • Hooke’s Law: the restoring force is proportional to the displacement of the object. • Displaced objects have potential energy. • Objects vibrate in simple harmonic motion if they behave according to Hooke’s Law (pendulums and mass-spring systems)

12. Measuring Simple Harmonic Motion • Amplitude: the maximum displacement of the object • Period: time for one complete cycle (Seconds) • Frequency: how many cycles completed per second (Hz)

13. Pendulums and Mass-Spring Systems • Period of a pendulum depends on pendulum length. • Period of a mass spring system depends on mass and spring stiffness.

14. Wave Types • Mechanical waves disturb a physical medium. Non-mechanical waves, like light, do not need a medium to travel through. • Pulse waves are a single peak traveling. Periodic waves are repeated regular motions.

15. Waves Continued • Transverse waves are perpendicular to wave motion. • Longitudinal waves are parallel to wave motion

16. Wave Speed • The speed of a wave is constant for any given medium. • Frequency and wavelength are inversely proportional.

17. Interference • When waves collide with each other, it is called interference. • If the waves peaks are in the same direction, they add together for constructive interference. • If the peaks are in opposite directions, they subtract for destructive interference.

18. Standing Waves • Standing waves can be generated only at certain wavelengths relative to the length of the medium (L). • 2L • L • (2/3)L • (1/2)L • (2/5)L • etc.

19. Homework • Finish study guide and check solutions. • Review all slides, and get a good night’s sleep.