1999-00 -- 05-06 Academic Years
30 September 1997: Comment by Alex Junievicz
A comment on a fuel commercial:. Running full blast then stopping is a way of getting maximum gas economy on a car. [allegedly!!] The engine is at maximum efficiency at High output, thus accelerating and coasting and accelerating. and coasting is a bad way to drive, but gets better gas mileage.
04 December 2001: Don Kanner (Lane Tech HS, Physics) Jury Duty
Don described a [let us say, purely hypothetical] situation in which two occupants of the front seat of a car made 3 consecutive left turns in the car, while traveling at a constant speed of about 15 miles/hour [5 meters/sec]. The passenger described the following sequence of events
There was some discussion as to whether this sequence of events could have occurred as described. Was either the passenger or the driver at fault? What do you think about this purely hypothetical situation?
20 January 2002: Arlyn Van Ek (Iliana Christian HS) Why are
there headrests on automobile
Arlyn put this question on a test recently, expecting students to say that they would provide protection from "whip-lash" in rear-end collisions. However, many students commented that they would also protect in front-end collisions, as well. Namely, the occupant's head goes forward, bounces off the air bag, and then snaps backward, to be stopped by the headrest. Is this correct?
19 March 2002: Bill Colson (Morgan Park HS Math) -- Horsepower and
Torque in Internal
Bill passed out information on two recent Chicago Tribune articles on torque and horsepower, in which it was explained that engines produce different amounts of torque and horsepower at different engine rpm. The horsepower increases linearly with engine rpm, whereas the torque generally increases more erratically. Bill Shanks said that, at lower rpm, one should go into a lower gear to provide greater torque to the drive shaft. He also pointed out that bicycles were 3-5 times as efficient as, say, walking, in energy expenditure. Porter Johnson remarked that European horsepower is somewhat lower than the American variety --- 736 Watts versus 745 Watts. I guess there must be something in the oats over there! For additional information, see the websites Horsepower and Torque; A Practical Explanation: http://www.car-videos.net/articles/horsepower_torque.asp and Power and Torque: http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm.
28 January 2003: Bill Shanks [Joliet Central HS,
Physics of Car Shopping
Bill has been investigating the new hybrid vehicles: the smaller models Toyota Prius® and Honda Insight®, as well as the larger Honda Hybrid Civic®. In these vehicles the primary source of propulsion is an electric motor, which is run by batteries that are kept charged by a small [7 horsepower] gasoline engine. As the vehicles slow down, the energy released is used to maintain the charge on the batteries, rather than merely being dissipated as heat. The gasoline engine also serves as a supplemental energy source when needed. These vehicles are about twice as efficient as comparable sub-compact cars run completely by gasoline engines, and would represent significant savings in fuel.
The Honda Insight, which can be obtained for about $17K, is a two-seater with a mass of about 850 kg, and the fully loaded vehicle might have a mass of about 1000 kg. The battery package is rated at a capacity of 6.5 Ampère hours, at a potential of 144 Volts (or Joules/Coul). Bill calculated that the battery held an energy
Bill then asked for the maximum speed of the vehicle, starting from rest and acting on batteries alone. The answer is that the energy available should be equal to 1/2 mv2, or
The maximum speed, v = 82 meters/second, or about 180 mph, should suffice for most of us.
You really took us for a ride. Thanks, Bill!
11 March 2003: Bill Shanks [Joliet Central HS, Physics,
retired] Fuel Efficiency of a Bicycle in
Bill calculated the fuel efficiency of a bicycle from data presented at a previous SMILE class, which indicated that 30 kilocalories [kcal] of food energy are required to ride one mile on a bicycle at a speed of about 18 miles per hour -- 30 kilometers per hour. He used the fact that 3700 kcal of food energy can be obtained from 1 pound of body fat, so that one may travel 3700/30 = 120 miles per pound of body fat. A gallon of fat should weigh about the same as a gallon of water --- approximately 8 pounds, so that one theoretically should be able to travel about 1000 miles per gallon of body fat. Who would have thunk it?
Bill also passed around an article by Charles Leroux in the 11 March 2003 issue of the Chicago Tribune, defining the Body Mass Index: BMI, which is computed in terms of a person's weight W [ in pounds] and height H [in inches] as
A BMI of 18-25 is considered Normal, 25-29 is considered Overweight, and above 30 is considered Obese. It was unclear as to where this number comes from, since it surely does not represent an accurate measure of a relevant parameter such as fat percentage.
An insightful combination of ideas, Bill!
07 October 2003: Ann Brandon [Joliet West HS,
physics] Inertia and Seat
Ann put a "bear crash doll" onto a physics collision cart, and released the cart at the top of a plank inclined at a moderate angle (about 30°) to the horizontal table. The cart rolled down the plank, off its edge, and onto the table. At that point the bear-doll flipped out of the cart, and landed on its head. This was a perfect illustration of Newton's Second Law: A force is needed to change the velocity of the bear. A force -- supplied when the bear-doll struck the table -- is required to change the direction of motion of the bear-doll; otherwise it would just keep going and going and going. It also illustrates the need to wear seat belts in an automobile. Next she strapped the bear into the cart with a rudimentary (rubber band) seat belt, and again released the cart from the top of the plank. This time, the bear whacked its head against the "dashboard", and experienced severe whiplash. Again, Newton's Laws are at work. Also, the need to wear shoulder straps, as well as seat belts, was shown by Ann, using an additional rubber band.
The collision of the two Boston Red Sox outfielders [Johnny
Damon and Damian
chasing after a pop fly during the baseball playoff games was
discussed. One of
the players suffered a concussion, and was unconscious for a few
although no brain damage apparently occurred as a result of the
A great danger in a concussion is brain swelling, which must be treated
to prevent permanent brain damage.
It was also mentioned in discussion that Princess Diana and all other occupants of the car died as a result of the automobile crash in Paris -- except for the front "shotgun" passenger, who was wearing a seat belt. See Princess Diana: Cause of Death: http://www.senderberl.com/diana.htm
Ann, you showed us the physics and importance of buckling up with these elegantly simple experiments!
09 December 2003: Porter Johnson asked the (not entirely hypothetical) question of whether a large (Volvo®) sedan could become "totaled" while running into the rear of a compact (Toyota®) sedan. Interestingly enough, this can happen, since the accelerometer sensor to release the air bags is located behind the grill on some Volvo sedans, as well as on certain other cars. If that grill is even slightly damaged, the sensor will cause both air bags to be deployed [essentially by firing explosive charges that resemble shotgun shells] --- which, in turn, often break the front windshield. When this occurs with a relatively mature vehicle, the cost of repair becomes greater than the "replacement cost" of the vehicle less the "salvage value" of the vehicle "cannibalized" for spare parts. The vehicle is thus deemed a total loss by insurance adjustors. This occurs, in spite of our naive assumptions based upon Newton's Laws of Motion. Fairy tales can come true; it can happen to you ... occasionally!
09 December 2003: Karlene Joseph [Lane Tech HS,
physics] Crash and Burn
Karlene showed us some video images of collisions of automobiles in which "crash dummies", as well as stunt drivers were sitting in the automobiles. The frame-by-frame sequence of images is quite fascinating. It was clear to all of us that, in fact, Newton's Laws fully explain the occurrences during the crash. In particular, when we saw the impact and damage when the head of the unrestrained occupant hit the dashboard, the warning "wear your seatbelts" was justified in graphic detail. These images are located on the website of The Center for Injury Control, School of Public Health, Emory University [http://www.sph.emory.edu/CIC/] on the Motor Vehicle Crash Video page.
Those daredevils and dummies showed how Newton's laws determine the course of collisions! Thanks, Karlene!
26 October 2004: Carl Martikean [Proviso East HS, Physics] called attention to the article entitled Cruise Control, which appeared on Dr Dobb's Journal, November 2004: http://www.ddj.com/. The article involves developing a (rather elaborate) strategy for tracking a fugitive on a desert road at night, using a network of sensors that have limited capability. Once again, kinematics comes to the rescue! Thanks, Carl!