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CHAPTER 3

CHAPTER 3. ENERGY. Common Units for Energy. Joule Calorie Conversion: 1 calorie = 4.181 Joules. Type of Energy. Potential Energy – the energy an object has due to its position Potential Energy (PE) = mgh PE = mass x acceleration due to gravity x height. Kinetic Energy.

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CHAPTER 3

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  1. CHAPTER 3 ENERGY

  2. Common Units for Energy • Joule • Calorie • Conversion: 1 calorie = 4.181 Joules

  3. Type of Energy • Potential Energy – the energy an object has due to its position • Potential Energy (PE) = mgh • PE = mass x acceleration due to gravity x height

  4. Kinetic Energy • Kinetic Energy = (1/2) mass x velocity2 • KE = (1/2) mv2

  5. Different Forms of Energy • 1. Chemical Energy – E involved in chemical reactions • 2. Mechanical Energy – E from machines • 3. Electrical Energy – E from electromagnetic interactions • 4. Nuclear Energy – E from the atom • 5. Radiant Energy – E that travels through space (Ex. Infrared radiation = heat radiation; microwaves, light)

  6. Law of Conservation of Energy • Energy can neither be created or destroyed. It can only be converted from one form to another. The total energy remains constant.

  7. Sources of Energy • Sun (solar) • Water (hydroelectric) • Coal • Biomass • Petroleum • Ocean • Wind • Hydrogen

  8. WORK • Work done on an object is defined as the product of force times the parallel distance through which the force acts. • Work = force x distance • W = Fd • = mgd or • = weight in lbs. x distance in feet (easier!) • Remember that: Force = mass x acceleration due to gravity

  9. 2 Requirements for WORK TO OCCUR • 1. Something must move. • 2. The movement must be in the same direction as the force applied. • No work is done if you’re simply holding your phone. Lifting the phone to your ear means the phone travelled a certain distance, so work was done on the phone.

  10. Units for Work • ft-lb • Joule • newton-meter (kg-m/s2) • Conversion: 1 joule = 1 newton-meter = 1 kg-m2/s2

  11. Sample Problems • (Easy) How much work is required to lift a 50 lb box vertically a distance of 2 ft? • (Harder) How much work is required to lift a 50 kg. box vertically a distance of 2 meters?

  12. POWER • Is defined as work per unit time. • Power = work time = w t • Units of power: Joules/second watt • Conversion: 1 J/s = 1watt

  13. Other unit for Power • Horsepower (hp) • Conversion: 1 hp = 746 watts • (Note: Your electric bill is measured in kWH or kilowatt hours)

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