PHYSICS OF RACING


There are many factors that go into racing and efficiency. It is not simply how the car runs, but how to make the car run well. Such as this, a Hummer H2 has a very high drag coefficient, but also has a large engine. Therefor the high drag coefficient negates the powerful engine, creating a very poorly performing car in both top speed and fuel efficiency.

Fuel efficiency starts from the pistons, where the fuel is initially combusted to move the pistons. This is also only discussing the details of a internal combustion engine, the only type of engine in most gasoline vehicles. The pistons fire, and then that pushes a rod which rotates the crankshaft. The crankshaft then, eventually, powers the wheels after going through the gears. All throughout this process is friction, which contributes partially to fuel efficiency as well. But wind resistance is a key factor as well.

Newton’s Laws and Racing


To understand this question it is necessary to understand the laws of motion. Newton’s first law states that objects in motion stay in motion unless outside forces act upon it. Now this concept is important to realize when taking corners, but not so necessary to realize in the drag (such as when determining maximum speed). But the second law is immensely important, this law states that anything with mass, such as the car, with a net force acting on it will accelerate. The tires, which initially is powered by the engine, grip the ground from friction and propel the car forward. This tire example also is the idea of the third law, every force has an equal and opposite force (friction in this case). Now we need to go further in depth with the idea of fuel efficiency.
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Wind Resistance


drafting.pngWind resistance is interesting in that in exponentially increases as speed increases. Such as if you are traveling at a rate of 20 miles per hour and you increase your speed to 40 miles per hour, the wind resistance on your car will quadruple. This directly relates to fuel efficiency in that the faster you are traveling in your car, the more air resistance is pushing back on you causing your fuel efficiency to drop. A Hummer gets less miles per gallon of gas than say a Dodge Neon gets due to the enormity of the Hummer which allows more wind to hit it head on causing more wind resistance. The flat front end of a Hummer makes it less aerodynamic than the rounded off front end of the Dodge Neon. This also has an effect on fuel efficiency because on the Dodge Neon the wind just rushes over the round front end while on the Hummer it hits the flat front end causing the wind to push back on it with greater force. In racing, drivers do a maneuver that is called drafting. Drafting is when one driver gets right up behind another driver and gains speed. The second driver gains speed because the first car is keeping the second from being effected by wind resistance. Down force is another way to explain the physics of the air resistance on cars.

Down force


On the other hand, down force is the downward thrust typically used by race car drivers to keep the tires gripped to the ground. Such as if a typical car began reaching high speeds, it will lose some grip to the ground typically causing the car to begin to drift or even lift off of the ground. This is why race cars have fins and spoilers, which increases the down force therefor increasing handling. Also if you have ever watched drag racing the most common cause of disastrous wrecks is caused by dragster lifting off the ground. This happens because the airflow below the car is enough to lift its weight, therefor this amount is weight added to the down force at a certain speed. To counter this you add a more powerful fin, with an angle greater than before from the ground which will add more down force. The problem with this is that it also adds more resistance creating a slower maximum speed. Therefore the driver has to find a balance for down force to achieve maximum speed safely. This is all directly related to just simply driving in a straight line, but turning is obviously essential in driving and racing both.

Weigh Transfer


Weight transfer is the transfer of weight inside of a vehicle that occurs while accelerating, or executing a turn. This is closely related to Newton’s first law of motion, which is also known as the law of inertia They are related because the weight of the car wants to continue going in a straight line as the car makes a turn causing the occupants to lean out of the imaginary circle of the turn. This is where it relates to down force. If the down force is not great enough, the car will begin to slide sideways in a straight line, also called drifting, which on a street is likely to cause a terrible accident like sliding into a guard rail or a pole. The down force is a necessity, but with too much it causes issues. Balancing the perfect amount of down force is the issue. But the down force is applied to the tires touching the track, and if the tires aren’t in good condition sliding becomes a much more likely scenario.

Friction and Tires


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Friction is what causes the tires to stick to the pavement. Tire pressure needs to also be balanced, a higher tire pressure will mean less surface in contact with the pavement as a lower tire will mean more surface area. The problem with too high of a tire pressure is that as the tire heats up it will increase the pressure, giving the tire a chance of bursting. Usually a high, but proper, tire pressure will be the best pressure to have in a vehicle for road driving. But in racing you want a lower tire pressure therefor greater grip. But, with lower tire pressure the treads can be placed unevenly creating increased area wear. This is why in racing such as NASCAR tires have to be changed regularly or else they will become dangerously smooth and thin and can cause an accident. Overall tires have to be set to the proper pressure for your use in them, lower for racing and higher for the roads. To obtain speed you have to have a decent engine though.




Engine Power


horsepower1.gifHorsepower is the term used to describe how powerful an engine is. It is what gets a vehicle up and going as well as being the force that accelerates the vehicle. This being said, it is still better to have a car with good aerodynamics than to have a car that has more power under the hood. This is because air resistance is squared as speed increases. But as speeds increase the engine power is necessary to keep going faster. Making it more aerodynamic simply decreases the amount of engine power to reach “X” speed. Such as an engine in a Hummer H2 and the same engine in a Ferrari. The aerodynamics of the Ferrari are going to give it a chance of going much more fast than the Hummer H2 although engine power is equal. Engines are actually quite inefficient though, which is what many researchers are striving to improve.

Fuel Efficiency and Breakdown


kwh_kg.jpgMuch of an vehicles energy does not go to kinetic motion, but instead to excess heat loss and exhaust. Actually it adds up to only about 30% of the energy is actually useful energy for the vehicle. Some interesting ideas that researchers have came up with is to use this heat energy to charge batteries, and to completely power the breaking system since the friction from the breaks creates so much excess heat. If 100% efficiency were possible you would be able to obtain numbers excess of 100 miles per gallon in a standard sedan, and even in vehicles such as the Hummer be able to reach the average sedan MPG which is approximately 24mpg. Engine efficiency is fairly important, especially since the pollution worries. Electrical engines will be able to obtain much better efficiency than gasoline cars once we have appropriate battery life.


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