Tekifest Physics V1.1

Physics

Before you can win, you have to learn where to go fast.

By Enrique Serrano

Content • Cockpit

• Mental Program • Braking • Weight Transfer • Acceleration • Drag • Centripetal forces • Introduction to the Racing line

• Tire Management • The Track

Physics

Cockpit • The race car seat, and your position in it, is more important than most racers ever think.

• This seating position should allow you to turn the steering wheel 180 degrees without any interference or moving of your hands on or from the wheel.

• Check this with the seat belts/safety harness done up tight.

• While seated, check to see if you can reach the shifter comfortably. You may have to modify or adjust the shifter to suit.

• You should also be able to fully depress the pedals and still have a slight bend in the legs.

• You want to use the balls of your feet on the pedals.

MIRRORS

Steering Wheel

Mirrors play a critical role in the race driver’s job.

It is just as important to know what’s behind and beside you as it is to know what’s in front.

The less you turn the steering wheel, the faster you will go.

Use your mirrors enough to always know who’s around you.

A competitor should never take you by surprise by being somewhere you didn’t expect.

Take time to adjust all your mirrors.

• Check your mirrors as often as it takes to always know where everyone else is around you.

With the 9 and 3 grip you should be able to steer through almost every corner without moving your hands from this position.

DRIVING SUBCONSCIOUSLY •

It is not possible to drive a race car effectively (fast, at the limit) by consciously thinking about each movement, maneuver, and technique.

•

A race car is much too fast to allow you the time to think through each function.

•

Your conscious mind cannot react and respond quickly enough to physically operate the controls of a race car at speed.

•

It must be a subconscious act. To do this, you have to program your mind, just like a computer. How? By practicing,

Mental Program.

• With repetition, your brain forms neural pathways or programs.

• Allowing you to head out on the track and simply execute the appropriate program at the appropriate time.

• Drive in your mind before driving on the track.

Gravedad g=gravedad 9.81 m/s

Newton • The first law: a car in straight-line motion at a constant speed will keep such motion until acted on by an external force.

The only reason a car in neutral will not coast forever is that friction, an external force, gradually slows the car down. Friction comes from the tires on the ground and the air flowing over the car. The tendency of a car to keep moving the way it is moving is the inertia of the car, and this tendency is concentrated at the CG point.

• The second law: When a force is applied to a car, the change in motion is proportional to the force divided by the mass of the car.

This law is expressed by the famous equation F = ma, where F is a force, m is the mass of the car, and a is the acceleration, or change in motion, of the car. A larger force causes quicker changes in motion, and a heavier car reacts more slowly to forces. Newton’s second law explains why quick cars are powerful and lightweight. The more F and the less m you have, the more a you can get.

• The third law: Every force on a car by another object, such as the ground, is matched by an equal and opposite force on the object by the car.

When you apply the brakes, you cause the tyres to push forward against the ground, and the ground pushes back. As long as the tyres stay on the car, the ground pushing on them slows the car down.

• Brakes work by converting the energy of motion, kinetic energy, into the energy of heat in the brakes.

Braking

• The time t required for braking from speed v can be calculated from: t = v / a which simply follows from the definition of constant acceleration. Given the time for braking, we can calculate the distance x, again from the definitions of acceleration and velocity.

• We can immediately see from this table (and, indeed, from the formulas) that it is the distance, not the time, that varies as the square of the starting speed v. The braking time only goes up linearly with speed, that is, in simple proportion.

• Excercise

• Learning to balance your car consistently and automatically is one essential part of becoming a truly good driver.

Weight Transfer

• Balancing a car is controlling weight transfer using throttle, brakes, and steering.

Weight Transfer • In this figure, the "pie plate" in the center is the Center of Gravity. • G is the force of gravity that pulls the car toward the center of the Earth. With the mass this is the weight of the car. • Ff is the lift force exerted by the ground on the front tire, and Fr is the lift force on the rear tire. These lift forces are as real as the ones that keep an airplane in the air, and they keep the car from falling through the ground to the center of the Earth.

•

Weight Transfer Excercise

By how much does Lf exceed Lr?

• Ff = dG + Bh / w, • Fr = (1 - d)G - Bh / w

B=Braking Force h= Gravity Center d= Weight Distribution G= Car weight e= Wheelbase

Trail Braking • Trail braking is when you gradually release, or trail, your foot off the brake pedal while turning into a corner.

• If you’ve completed your braking entirely and your foot is off the pedal at the point you begin to turn into the corner, then you have not trail braked at all. If you have even the slightest amount of brake pedal pressure on while turning into the corner, then you are trail braking.

• Some times your foot will finally be completely off the brake pedal within a foot or two past the turn-in point, and other times it will not be until you’re practically at the apex. Either way, you’re trail braking.

Left Foot Braking • One common race situation that requires left-foot braking is when a racer is cornering under power. If the driver does not want to lift off the throttle, potentially causing trailing-throttle oversteer, left-foot braking can induce a mild oversteer situation, and help the car "tuck", or turn-in better. Mild leftfoot braking can also help reduce understeer.

Heel-and-toe shifting • Heel-and-toe shifting is used before entry into a turn while a vehicle is under braking, preparing the transmission to be in the optimal range of rpm to accelerate out of the turn.

• • • •

We are approaching a corner at 80 mph.

We’re currently in 5th gear (yellow line) , The engine is revving at 8,000 rpm.

We want to downshift to 4th gear (purple line) At our current speed (80 mph) the engine will have to rev at 10,000 rpm when the downshift to 4th gear takes place

Acceleration • The first kinematic equation relates speed, time, and distance. If a car is moving at a constant speed or velocity, v, then the distance d it travels in • time t is d = vt or velocity times time.

• How far does a car go in one second?

¼ Mile calculation • How long will it take a car accelerating at ½G to do the quarter mile • ¼ Mile Excercise

Drag • How much horsepower does it take to go a certain speed? • An automobile moving at constant speed in a straight line on level ground is, in fact, acted on by a number of external forces that tend to slow it down. • The most important external, slowing-down force is air resistance or drag.

Drag Impact

• Exercise

•đ??š =

1 đ?‘?đ??´đ?œŒđ?‘ŁÂ˛ 2

Lower vehicle by 30mm..............-5% Open windows.............. +5% Wide wheel/tyres..............+2 to +4% Hidden headlamps (like an old porsche).............. +3 to +10% Door mirrors .............. +2 to +5% Airflow through radiator.............. +4 to +14% Brake cooling devices.............. +2 to +5% open sunroof .............. +2% Roof Rack.............. +40% (JUST THE ROOF RACK!!!)

Air Density

Centripetal Forces • When you turn the steering wheel, you are trying to get the front tyres to push a little sideways on the ground, which then pushes back, by Newton's third law. When the ground pushes back, it causes a little sideways acceleration. • In order to turn right, for example, a force, pointing to the right, must act on the car that veers it away from the straight line it naturally tries to follow.

• Centripetal forces exercise. • Angular Acceleration formula

2

a=đ?‘Ł /r

Thus đ?‘Ł = đ?‘Žđ?‘&#x;

Introduction to the Racing line

Understeer • Understeer means the car is not steering as much as wanted.

• when the front tires have less traction than the rears, and regardless of your steering corrections, the car continues “plowing” or “pushing” straight ahead to the outside of the turn.

Oversteer • Oversteer means it is steering too much. • The rear tires have less traction than the fronts, the back end begins to slide, and the nose of the car is pointed at the inside of the turn.

If the front breaks away first, your car has natural understeer, and if the rear slides first, it has natural oversteer.

Reference Points • To be consistent in your driving, you should use reference points. They are important for your concentration. • The less time and concentration you spend on determining the exact point where you begin your braking for a corner, for instance, the more you can spend on feeling how the car is reacting to your inputs.

• Three most important reference points are used to help guide you through the corners. They are, in order: 1.

the turn-in point

2.

Apex

3.

Exit point.

Racing line • The turn-in is probably the most important part of a corner, as this determines how you drive the rest of the corner, where and how fast you apex and exit. • As the name suggests, this is the part of a track where you do your initial turn of the steering wheel into the corner. And this turn-in point is determined somewhat by where you want to apex the corner.

Apex • The apex of a corner is the point, or area, where the inside wheels run closest to the inside of the road.

• Also called as the area of a turn where you are no longer driving into the corner but are now driving out. Also called the “clipping point,” as this is where your inside wheels clip past the inside of the roadway.

Apex • Determining whether or not you had the correct apex is simple. If you come out of the corner having to turn more to keep from running off the road, then you had too early an apex.

•

If you chose too late an apex, the car will not be using the entire road on the exit. It will still be too close to the inside of the corner.

• The faster the corner, the closer to the geometric line you should drive; the slower the corner, the more you need to alter your line with a later apex.

The most important corner is the fastest one leading onto a straightaway.

Symmetrical Curve • Exercise • Let’s start with the problem of only going through one corner

• 2D, no skid

• What Velocity is higher? Lm or Li?

Tires Thirty years ago, engineers believed that one G was theoretically impossible from a tire.

Tires • There are only three factors that determine the amount of traction you have available from the tires.

1. The friction coefficient Îź between the tire and the track surface, which is determined by the road surface itself and the rubber compound of the tire.

2. The size of the surface of the tire that contacts the track surface. Obviously, the more rubber in contact with the road surface, the more traction available.

3. The vertical load on the tires. This load comes from the weight of the vehicle and the aerodynamic downforce on the tires.

Grip Angle • The angle between the direction the tire is pointing and the path the wheel is following is the grip angle. • An understeering car has larger grip angles in front, and an oversteering car has larger grip angles in the rear. • The greater the grip angle, the larger the cornering force becomes, up to a point. After this point, greater grip angle delivers less force

Friction Coefficient • The coefficient of static friction is not exactly a constant. Under driving conditions, many effects come into play that reduce the friction of a good tire to somewhere around 1.20G.

• These effects are tire deflection, suspension movement, temperature, inflation pressure, etc.

But the proportionality law still holds reasonably true under these conditions.

• Exercise

Friction Coefficient Accelerating gives the front tyres less stiction and the rear tyres more

Traction Budget Chart • We often like to speak of the sideways acceleration the car can achieve, we can converts force into acceleration in G’s by dividing

by W, the weight of the car μ can thus be measured in gees.

Race Chrono

Lateral Acceleration (G) 1.5

1

0.5

0 -1.5

-1

-0.5

0 -0.5

-1

-1.5

0.5

1

1.5

Tires • Tyre sounds very informative and always listen to them while driving

You can only use 100 percent of the tires’ traction, and make sure you do.

The Track • Learning the track means recognizing and placing in your mind every tiny mark, bump, color change, and shape of every inch of the track. The bigger your database of reference points, the better you have learned the track.

The Edge • learning the ideal line around a track, it is important to use all the track surface, even if that means forcing the car toward the edge of the track.

The Track • After the ideal line becomes a habit, a subconscious act, you can begin to work on driving at the limit.

• With each lap, begin accelerating a little earlier and harder out of each • Keep accelerating earlier until you either begin to run out of track or the car begins to understeer or oversteer excessively

The Track • Once you feel you’re getting close to the limit under acceleration (on the ideal line), then begin to work on your corner-entry speed.

• Working on the fastest corners first then into the slowest, carry a little more speed into the turn each lap, until you can’t make the car turn in toward the apex the way you would like, until it begins to understeer or oversteer.

Every inch of track you are not using is costing you speed.

You paid for it, so use it all.

"What I hear I forget, what I see I remember, what I do I understand."

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• Espejos grafica con los angulos • Microfono