The Laws of Physics • The man-made laws we have discussed so far, can be good or even unreasonable. They also need police enforcement, a judge and jury to convict. • Natural laws that control our universe, need no police or courts, they will enforce themselves.
Stay within the law • It is our job to know and understand the natural laws that are going to effect vehicle handling characteristics. To break a natural law (or attempt to) might have dire consequences.
Some of the laws that effect us • Gravity is the force that tends to pull all objects toward the center of the earth. Gravity obviously will effect acceleration and braking when going up or down hills.
SUVs • The center of gravity is the point around which all the weight in a vehicle is centered or balanced. The higher the center of gravity, the more likely the vehicle to roll over. A major concern with sport utility vehicles (SUV) is their tendency to flip in a collision. The center of gravity can be too far forward or backwards due to vehicle design or load. This too can cause handling problems.
Did you know? • All the weight added to an SUV raises the center of gravity. • Most SUVs are rated for 800 lbs or less total passenger/luggage weight.
Keeping you straight • Inertia is a body at rest stays at rest, a body in motion stays in motion in a straight line until acted upon by an outside force. • When you go into a turn, it is inertia trying to pull you into the woods. • When you are stuck in the mud or snow, it is inertia that keeps you from moving. • When you are sliding through an intersection, it is again, inertia.
Friction • Friction is resistance to motion between any two objects that touch. • That can be your brakes, clutch, tires or even your internal engine parts. • About 30% (or more) of fuel cost is to overcome engine friction. • It might be you and your mother-in-law. She is not moving! You miss so much taking this class online.
How much friction? • Coefficient of friction is the measurement of friction. • You can figure the coefficient of friction by dividing the force that it takes to move across the object, by the weight of the object.
Some examples: • A. Dry asphalt is .78B. Wet asphalt is .60C. Dirt roads are .20D. Dry snow is .20E. Wet snow is .lO • Notice the difference between wet and dry roads is almost 25%. That means your stopping distance is 25% longer when it starts to rain. • BACK OFF!!
tractions: • Each are to overcome inertia (rest, motion, straight line).1. Acceleration traction2. Braking traction3. Cornering traction • Notice: Brake is not spelled break, that is what your mind is doing about now. Taking a break. • Brought to you at no additional charge.
There are many things which can affect traction • 1. Tires:a. Type. Most tires now are radials and are really good. You can check the tire’s traction rating on the tire, or from the manufacture. b. Wear. Tire tread is designed to get water out from under your tires when driving. The law allows 2/32” tread before you must replace them. Replace them at 4/32” or before. c. Inflation. The proper inflation is on the tire, inside the door or in you owner’s manual. I suggest the tire sidewall is best. They designed the tire for many vehicles. They should know best.
Road Surfaces a. Asphalt. Most roads. b. Concrete. Many freeways, lasts longer and has better traction, especially when wet.c. Gravel. Not good for much.d. Dirt. Even worse. Slide #9 explained the traction of these types of roads.
Condition of the road surface • Dry • Wet • Snow • Ice • Hot • Cold
Other things that may affect traction • 4. Weight of vehicle5. Type of vehicle6. Bank of road/curve7. Speed of vehicle8. Driver response9. Temperature of road/tires
Conclusion • The amount of rubber that is actually touching the road is very small. • All that you have is riding on those four small spots. • Slow down, buy good quality tires, and replace worn tires.
Check your tires PSI • Proper tire inflation is critical to handling ofthe vehicle, life of the tire and gas mileage. • You are in control of your tire’s inflation, gas stations don’t do it, it is your responsibility to make sure you keep them properly inflated. • You need to check them at least once a month. • Nitrogen molecules are larger than oxygen so some are using nitrogen to inflate tires because the inflation stays correct longer. Not sure it is worth the price, your call. (about $40 for 4)
Here’s the propaganda •  Nitrogen is denser than Oxygen: This means the larger molecules escape less easily from tires resulting in a more gradual loss of pressure over time. According to the Michelin Tire Manual, a tire that is inflated with Nitrogen loses its pressure 3 times slower than if it were inflated with air. •  Nitrogen is moisture free: Pure Nitrogen inflated tires experience less steel belt and rubber degradation. Nitrogen use also reduces valve and wheel corrosion. •  Nitrogen provides longer tire life: Nitrogen inflated tire run cooler and require less maintenance according to the Goodyear application bulletin. •  Nitrogen is non-flammable: Nitrogen technology has been used in aircraft, military and race car technology for over thirty years.
Tire ratings • Tires have three ratings for consumers to make better choices. • First is a mileage rating. A 100 rating is supposed to mean the tire should last 30,000 miles. A 200 rating then, should last 60,000. Although the rating may be inaccurate, they can be used for comparison shopping. • Secondly, is a temperature rating. A being the best, B not as good, C being the lowest rating. C rated tires should not be used in hot weather or severe road conditions. • The last rating is a traction rating. This rating is specifically a wet road braking rating. Again A is the highest, C is the lowest. • There are other ratings, generally for racing. There is also a AA traction rating. Most of us will deal with the three ratings mentioned above.
Total Stopping Distance • The three parts of total stopping distance are:1. Perception time/distance2. Reaction time/distance3. Braking distance • At 60 MPH, you are moving at about 90’ per second. Therefore, if it takes you several seconds to recognize and react to a situation, you may have traveled hundreds of feet.
Kinetic Energy • Kinetic energy is energy of motion. Potential energy stored within a moving object. Kinetic energy is determined by speed and weight of an object. • KE= 1/2weight x (speed squared)/32.2 • Since we are determining foot pounds of kinetic energy, speed is in feet per second. Ft/sec = 1.5 X MPH
For example: • A 3000 pound vehicle, traveling at 60MPH has 57,547 foot pounds of KE. • The fat head in the back seat behind you, a 180 lb person at 30 MPH, has 5,600 foot pounds of KE. Make sure he/she has their seat belt on, or you are going to catch them as they rip through the seat, and you, on their way to the dash and beyond.
One last step • Force of impact is kinetic energy (KE) divided by stopping distance (in feet). The longer the distance, the less severe the force of the impact. • Seat belts tie you to the vehicle to stop you over a longer distance, with the vehicle. Therefore, significantly reducing the force of the impact. • Airbags help by giving you a larger surface area to help distribute the force even more. • Airbags and seat belts together, reduce the chance of death or serious injury, by nearly 80%.
Conclusion • Buy a vehicle with airbags. • Buy a larger car. • Buy a higher car. • Wear your seat belt • Have others in your vehicle wear theirs. • Drive alcohol and drug free. • Slow down, back off. • If you do, you have significantly reduced your probably of dying in a crash. Remember, 40% of you will be involved is a serious crash, sometime in their lives. Prepare to crash. In all likelihood, you will.
Second conclusion • The natural laws will enforce themselves. • It is our job to understand them and to stay within them.