insaneracin2003
05-26-2006, 02:22 PM
I found this on another site;
The physics of ATV motocross (Part 1)
by Gary F. Stevens
copyright 2006
Newton’s laws (as they pertain to quad racing)
When Sir Isaac Newton (1643-1727) contemplated his laws of motion, it is doubtable that he had racing in mind. Yet today, the understanding of these laws and other principles of physics plays an undeniable role in how successful any quad racer is. This is the first installment on of a series that introduces the physics and math of racing ATV motocross.
Newton's First Law of Motion:
A quad at rest tends to stay at rest and an quad in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an external force.
The only reason a quad in neutral will not coast forever is that friction, an external force, gradually slows the quad down. Friction comes from the tires on the ground, wheel bearings and the air flowing all over the quad. The tendency of a quad to keep moving the way it is moving is the inertia of the quad, and this tendency is concentrated at the Center of Gravity point.
The center of gravity is a point on the quad that is typically a few inches above the case of the engine. Although when a rider gets on the quad, the center of gravity moves proportionately to the weight and size of the rider.
One of the basic laws of physics with race quads is that the wider the quad, the faster it corners. Curves on a motocross track offer special challenges to race quad riders because of physics principles. Newton's First Law brings us face-to-face with inertia. Because of inertia, the race quad (and rider) would continue on a straight line, non-curving track if some force were not applied. The force must produce a change in direction toward the center of the curve. This type of force that acts perpendicular to the quad's velocity is called centripetal force (not centrifugal!). It serves to change direction but not speed. The friction between the tires and the track provide that force. The force is directly related to the square of the speed of the quad. If a quad goes too fast, the friction force is not great enough to hold the quad in the track. The centripetal (center-seeking) force is also inversely related to the radius of the curve. The bigger the radius of turning the less force needed to make the curve. Most tracks are banked (tilted) toward the center of the curving section to help friction hold quads on the track at high speeds.
Newton’s Second Law of Motion:
When a force is applied to a quad, the change in motion is proportional to the force divided by the mass of the quad.
This law is expressed by the famous equation F = ma, where F is a force (torque), m is the mass (weight) of the quad, and a is the acceleration, or change in motion, of the quad. A larger force causes quicker changes in motion, and a heavier quad reacts more slowly to forces. Newton's second law explains why fast quads are powerful and lightweight. The more torque and the less weight the quad has, the faster it will accelerate.
So why are we using torque and not horsepower? It's important to understand that there is not anyone who actually measures horsepower from a running engine. What is actually measured on a dynamometer is torque. A dynamometers output is expressed in foot pounds. Using torque we can then calculate horsepower by converting the twisting force of torque into the work units of horsepower.
The Scottish Engineer and inventor, James Watt (1736-1819), introduced the term "horsepower". The term was and is used to indicate the rate at which
an engine can deliver work. It is a measure of power that indicates the energy produced or worked done by an engine per unit time.
According to Watt, 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of that weight into 33,000 foot pounds, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. Thus, the following formula applies for calculating horsepower from a torque measurement:
Horsepower = (torque * RPM) / 5252
How does that relate to quad racing?
Any quad, in any gear, will accelerate at a rate that matches its torque curve exactly. In other words, a quad will accelerate the fastest at its peak torque in any gear, and will not accelerate as fast below or above that peak. Torque is the only thing that a rider feels, and horsepower is just sort of an cryptic measurement in that perspective. 20 foot pounds of torque will accelerate a quad just as fast at 3500 rpm as it would if it were making that torque at 7000 rpm in the same gear. Though the formula shows that the horsepower would double at 7000 rpm. Consequently, horsepower isn't really that meaningful from a riders perspective. It is interesting to note that at 5252 rpm, horsepower and torque are always equal.
In contrast to a torque curve, horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising
Experiment: Take your quad to its torque peak in first gear and get in the throttle. Notice the roost behind you. Now take it to the power peak and get it the throttle. Do you notice a difference in the size of the roost?
It should be pointed out that in racing, it is better for an engine to make torque at higher rpm than a lower rpm, because you can take advantage of gearing.
Newton’s Third Law of Motion:
Every force on a quad by another object, such as the ground, is matched by an equal and opposite force on the object by the quad.
We have all heard the saying, "For every action, there is an equal and opposite reaction." As we know there is lots of action in quad racing.
When you are traveling at any rate of speed and apply the brakes, you cause the tires to push forward against the ground, and the ground pushes back. The force on the tires pushes on the wheels and in turn pushes on the suspension parts, which pushes on the rest of the quad, slowing it down.
During acceleration, the weight of the quad transfers more to the rear tires. By using proper body position, this can work to the riders advantage. By shifting body weight forwards, it can help keep the front tires more in contact with the ground while shifting body weight backwards can aid in traction in loose dirt.
Corning causes the weight of the quad to transfer to the left or right tires depending on which way the rider turns. This can be offset by the rider getting off the seat and positioning their body more to the inside of the turn. This allows a high rate of speed through the turn.
The physics of ATV motocross (Part 1)
by Gary F. Stevens
copyright 2006
Newton’s laws (as they pertain to quad racing)
When Sir Isaac Newton (1643-1727) contemplated his laws of motion, it is doubtable that he had racing in mind. Yet today, the understanding of these laws and other principles of physics plays an undeniable role in how successful any quad racer is. This is the first installment on of a series that introduces the physics and math of racing ATV motocross.
Newton's First Law of Motion:
A quad at rest tends to stay at rest and an quad in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an external force.
The only reason a quad in neutral will not coast forever is that friction, an external force, gradually slows the quad down. Friction comes from the tires on the ground, wheel bearings and the air flowing all over the quad. The tendency of a quad to keep moving the way it is moving is the inertia of the quad, and this tendency is concentrated at the Center of Gravity point.
The center of gravity is a point on the quad that is typically a few inches above the case of the engine. Although when a rider gets on the quad, the center of gravity moves proportionately to the weight and size of the rider.
One of the basic laws of physics with race quads is that the wider the quad, the faster it corners. Curves on a motocross track offer special challenges to race quad riders because of physics principles. Newton's First Law brings us face-to-face with inertia. Because of inertia, the race quad (and rider) would continue on a straight line, non-curving track if some force were not applied. The force must produce a change in direction toward the center of the curve. This type of force that acts perpendicular to the quad's velocity is called centripetal force (not centrifugal!). It serves to change direction but not speed. The friction between the tires and the track provide that force. The force is directly related to the square of the speed of the quad. If a quad goes too fast, the friction force is not great enough to hold the quad in the track. The centripetal (center-seeking) force is also inversely related to the radius of the curve. The bigger the radius of turning the less force needed to make the curve. Most tracks are banked (tilted) toward the center of the curving section to help friction hold quads on the track at high speeds.
Newton’s Second Law of Motion:
When a force is applied to a quad, the change in motion is proportional to the force divided by the mass of the quad.
This law is expressed by the famous equation F = ma, where F is a force (torque), m is the mass (weight) of the quad, and a is the acceleration, or change in motion, of the quad. A larger force causes quicker changes in motion, and a heavier quad reacts more slowly to forces. Newton's second law explains why fast quads are powerful and lightweight. The more torque and the less weight the quad has, the faster it will accelerate.
So why are we using torque and not horsepower? It's important to understand that there is not anyone who actually measures horsepower from a running engine. What is actually measured on a dynamometer is torque. A dynamometers output is expressed in foot pounds. Using torque we can then calculate horsepower by converting the twisting force of torque into the work units of horsepower.
The Scottish Engineer and inventor, James Watt (1736-1819), introduced the term "horsepower". The term was and is used to indicate the rate at which
an engine can deliver work. It is a measure of power that indicates the energy produced or worked done by an engine per unit time.
According to Watt, 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of that weight into 33,000 foot pounds, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. Thus, the following formula applies for calculating horsepower from a torque measurement:
Horsepower = (torque * RPM) / 5252
How does that relate to quad racing?
Any quad, in any gear, will accelerate at a rate that matches its torque curve exactly. In other words, a quad will accelerate the fastest at its peak torque in any gear, and will not accelerate as fast below or above that peak. Torque is the only thing that a rider feels, and horsepower is just sort of an cryptic measurement in that perspective. 20 foot pounds of torque will accelerate a quad just as fast at 3500 rpm as it would if it were making that torque at 7000 rpm in the same gear. Though the formula shows that the horsepower would double at 7000 rpm. Consequently, horsepower isn't really that meaningful from a riders perspective. It is interesting to note that at 5252 rpm, horsepower and torque are always equal.
In contrast to a torque curve, horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising
Experiment: Take your quad to its torque peak in first gear and get in the throttle. Notice the roost behind you. Now take it to the power peak and get it the throttle. Do you notice a difference in the size of the roost?
It should be pointed out that in racing, it is better for an engine to make torque at higher rpm than a lower rpm, because you can take advantage of gearing.
Newton’s Third Law of Motion:
Every force on a quad by another object, such as the ground, is matched by an equal and opposite force on the object by the quad.
We have all heard the saying, "For every action, there is an equal and opposite reaction." As we know there is lots of action in quad racing.
When you are traveling at any rate of speed and apply the brakes, you cause the tires to push forward against the ground, and the ground pushes back. The force on the tires pushes on the wheels and in turn pushes on the suspension parts, which pushes on the rest of the quad, slowing it down.
During acceleration, the weight of the quad transfers more to the rear tires. By using proper body position, this can work to the riders advantage. By shifting body weight forwards, it can help keep the front tires more in contact with the ground while shifting body weight backwards can aid in traction in loose dirt.
Corning causes the weight of the quad to transfer to the left or right tires depending on which way the rider turns. This can be offset by the rider getting off the seat and positioning their body more to the inside of the turn. This allows a high rate of speed through the turn.