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Physics and Astronomy Outreach Program at the University of British Columbia

Transportation Energy Use in Cars 3: Rolling Resistance. Lecture Notes. Physics and Astronomy Outreach Program at the University of British Columbia. Rolling Resistance. Question. Why would the pressure in our car tires affect gasoline consumption?

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Physics and Astronomy Outreach Program at the University of British Columbia

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  1. Transportation Energy Use in Cars 3: Rolling Resistance Lecture Notes Physics and Astronomy Outreach Program at the University of British Columbia

  2. Rolling Resistance Question • Why would the pressure in our car tires affect gasoline consumption? • Rolling resistance accounts for all the small bits of friction within the car, and more significantly, the friction within the tires and the road • Rolling resistance affects the motion of a car • Underinflated tires affect the fuel consumption of a car Physics and Astronomy Outreach Program at the University of British Columbia

  3. Rolling Resistance Background Energy from the fuel in a car goes to 4 main Places: Accelerating the car up to its cruising speed Overcoming air resistance Overcoming rolling resistance Heat (partly converted to motion, flowing to the environment with exhaust gases and by convection cooling of the engine) Physics and Astronomy Outreach Program at the University of British Columbia

  4. Rolling Resistance Background Rolling resistance is commonly approximated a constant frictional force, dependent on the weight of the car (similar to any other kind of friction) Physics and Astronomy Outreach Program at the University of British Columbia

  5. Rolling Resistance Background The coefficient of rolling resistance is usually written as . It has different values for different vehicle types: Physics and Astronomy Outreach Program at the University of British Columbia

  6. Rolling Resistance Approach • To figure out how the resistance force impacts fuel economy, we need to figure out how much energy is required to overcome it. • For this, use the Work-Energy principle (shows how much energy a force will add to the system) Physics and Astronomy Outreach Program at the University of British Columbia

  7. Rolling Resistance Approach • Rolling friction opposes vehicular motion; it thus subtracts energy from the car which is made up by burning more fuel • For a typical sedan (1200kg) plus driver (70kg), the rolling resistance will be: Physics and Astronomy Outreach Program at the University of British Columbia

  8. Rolling Resistance Approach Over the course of driving one kilometre, this will require extra energy given by: Physics and Astronomy Outreach Program at the University of British Columbia

  9. Rolling Resistance Approach Calculating the Fuel Requirement, Per km We can calculate the fuel requirement using the efficiency formula: Physics and Astronomy Outreach Program at the University of British Columbia

  10. Rolling Resistance Approach Calculating the Fuel Requirement, Per km And to provide this amount of energy, we need to use: Physics and Astronomy Outreach Program at the University of British Columbia

  11. Rolling Resistance Interpretation • We need 0.023 L of fuel per km to overcome frictional rolling resistance (at 100 km/h) • Added to the 0.064 L/km to overcome air resistance, the total energy needed to overcome resistive forces is 0.087 L/km (at 100 km/h) • This is slightly higher than the reported average of 0.076 L/km, but is reasonable since we calculated it at a high speed of 100 km/h Physics and Astronomy Outreach Program at the University of British Columbia

  12. * Model of a car with 40 psi tires Rolling Resistance Impact of Low Tire Pressure Physics and Astronomy Outreach Program at the University of British Columbia

  13. Rolling Resistance Bibliography a.b. Natural Resources Canada. Tire Inflation (online). http://oee.nrcan.gc.ca/transportation/personal/driving/autosmart-maintenance.cfm#h [25 August 2009]. MacKay DJC. Sustainable Energy - Without the Hot Air (Online). UIT Cambridge. p.262. http://www.inference.phy.cam.ac.uk/sustainable/book/tex/ps/253.326.pdf [25 August 2009]. Wikimedia Foundation Inc. Gasoline (Online). http://en.wikipedia.org/wiki/Gasoline [25 August 2009]. A Discovery Company. How Tires Work (online). http://auto.howstuffworks.com/tire4.htm [25 August 2009]. MacKay DJC. Sustainable Energy - Without the Hot Air (Online). UIT Cambridge. p.31. http://www.inference.phy.cam.ac.uk/sustainable/book/tex/ps/1.112.pdf [25 August 2009]. Physics and Astronomy Outreach Program at the University of British Columbia

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