Chapter 6 Energy Conversions and Efficiency Simple Systems

Simple Systems: Pendulums • Pendulums continuously convert between Ep and Ek • When we

Pendulum simulation If we ignore energy loss to friction, total energy is equal anywhere

Example • A pendulum with a mass of 1. 0 kg is raised 0.

• At the top, all energy is Ep Ep = mg∆h = (1.

• A 35 kg girl on a trampoline gains 500 J of gravitational

6. 1 Efficiency of Energy Conversions Calculating Efficiency • Efficiency is a ratio and

• A cyclist uses 52 k. J of energy in a 100 km

• Look at Model Problem 1 page 225 – 226 • Do Practice

• Do Workbook BLM 6 -2 Calculating Efficiency • Do Check Your Understanding

6. 2 Energy Efficiency and the Environment • • The average car is only

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Chapter 6 Energy Conversions and Efficiency

Simple Systems: Pendulums • Pendulums continuously convert between Ep and Ek • When we release a pendulum, Ep is converted to Ek until it reaches the lowest point (2). • At this point the pendulum is at Vmax and all of its energy is Ek • At the highest points, the pendulum stops momentarily before changing direction (1 and 3) Here all of its energy is Ep

Pendulum simulation If we ignore energy loss to friction, total energy is equal anywhere along the pendulum's path EP= mg∆h Ek = ½ mv 2

Example • A pendulum with a mass of 1. 0 kg is raised 0. 5 m above its resting point. Calculate the maximum speed of the pendulum.

• At the top, all energy is Ep Ep = mg∆h = (1. 0 Kg)(9. 81 m/s 2)(0. 5 m) = 4. 905 J • Max speed is at the bottom where all energy is Ek and we now know how much energy is in the system. • Ek = ½ mv 2 4. 905 J = ½(1. 0 Kg)(v)2 V= 3. 312 m/s

• A 35 kg girl on a trampoline gains 500 J of gravitational potential energy at the top of her bounce. Find the elastic potential energy of the trampoline

• A 35 kg girl on a trampoline gains 500 J of gravitational potential energy at the top of her bounce. Find the elastic potential energy of the trampoline • 500 J

• A 35 kg girl on a trampoline gains 500 J of gravitational potential energy at the top of her bounce. How high does she bounce?

• A 35 kg girl on a trampoline gains 500 J of gravitational potential energy at the top of her bounce. How high does she bounce? Ep = mgh h = Ep = 500 J = 1. 5 m m (35 kg)(9. 81 m/s 2)

• Video Mon. D Physics of Fun

6. 1 Efficiency of Energy Conversions Calculating Efficiency • Efficiency is a ratio and is expressed as a percent. • Output and input energies must use the same units. Efficiency = useful output energy × 100% total input energy or Efficiency = Eout × 100% Ein

• A cyclist uses 52 k. J of energy in a 100 km race. If he averages 50 km/h and the total mass of bike and rider is 80 kg, what is his % efficiency?

• A cyclist uses 52 k. J of energy in a 100 km race. If he averages 50 km/h and the total mass of bike and rider is 80 kg, what is his % efficiency? • • Ein = 52 k. J = 52 000 J Eout = Ek Vave = 50 km/h = 13. 88889 m/s m = 80 kg

• A cyclist uses 52 k. J of energy in a 100 km race. If he averages 50 km/h and the total mass of bike and rider is 80 kg, what is his % efficiency? • Ein = 52 k. J = 52 000 J • Eout = Ek • Vave = 50 km/h = 13. 88889 m/s • m = 80 kg Ek = ½ mv 2

• Look at Model Problem 1 page 225 – 226 • Do Practice Problems page 227 # 1 -9

• Do Workbook BLM 6 -2 Calculating Efficiency • Do Check Your Understanding p. 231 #1 - 5, 7

6. 2 Energy Efficiency and the Environment • • The average car is only 20% efficient. Incandescent light bulbs are only 5% efficient. Compact fluorescents are 20% efficient For every litre of gasoline burned 2. 4 kg of CO 2 is released into the atmosphere. • Read P. 232 – 241 and do P. 242 # 1 -9