Tractive Effort and Train Resistance
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Questions and Answers

What is the formula for calculating force as described in the content?

  • Force = Energy / Distance
  • Force = Speed / Energy
  • Force = Power / Speed
  • Force = Mass x Acceleration (correct)

    • How does tractive effort (TE) behave in the speed range of 0 to 20 mph?

  • TE increases at an accelerating rate
  • TE is variable and unpredictable
  • TE decreases monotonically with speed
  • TE is constant (correct)

    • What is the relationship between power, force, and speed?

  • Power = Force + Speed
  • Power = Force x (Distance / Time) (correct)
  • Power = Force / Speed
  • Power = Speed / Force

    • What is the maximum tractive effort (TE) value described in the example?

    <p>100 kN</p> Signup and view all the answers

    How is energy consumed in moving an object defined?

    <p>Energy = Force x Distance</p> Signup and view all the answers

    What happens to acceleration as speed increases beyond 20 mph according to the content?

    <p>Acceleration begins to decrease</p> Signup and view all the answers

    How do you convert speed from mph to m/s as demonstrated in the example?

    <p>Divide by 2.2</p> Signup and view all the answers

    What is the calculated power at a speed of 20 mph with a maximum TE of 100 kN?

    <p>910 kW</p> Signup and view all the answers

    What is the Maximum Power at Rail primarily focused on?

    <p>Power needed to actually move the train</p> Signup and view all the answers

    What characterizes Continuous Tractive Effort?

    <p>Power maintained during continuous motion</p> Signup and view all the answers

    What is the purpose of 'back emf' in a DC motor?

    <p>To oppose the applied voltage</p> Signup and view all the answers

    How is Starting Tractive Effort defined?

    <p>Effort required to start moving from a stop</p> Signup and view all the answers

    What limits the Short Term Tractive Effort?

    <p>Overheating of traction motors and transmission</p> Signup and view all the answers

    Which factors can influence Continuous Power rating?

    <p>Equipment characteristic and time proportions</p> Signup and view all the answers

    Why does the total power drawn from the supply exceed 910kW?

    <p>Because of auxiliary loads and conversion losses</p> Signup and view all the answers

    How long can Short Term Tractive Effort typically be sustained?

    <p>For a prescribed short period of time</p> Signup and view all the answers

    What happens to the maximum power curve at speeds over 70 mph?

    <p>It dips noticeably</p> Signup and view all the answers

    Which component is NOT a part of the calculation for Tractive Effort?

    <p>Horsepower</p> Signup and view all the answers

    What happens to the torque when the motor speeds up and the internally generated voltage rises?

    <p>The torque falls.</p> Signup and view all the answers

    What is the Balancing Condition in relation to train acceleration?

    <p>When the torque produced by the motors matches train resistance.</p> Signup and view all the answers

    What does the specific resistance 'R' during a run depend on?

    <p>The static and dynamic factors of the train.</p> Signup and view all the answers

    In the train resistance formula, what does the term 'cv^2' represent?

    <p>Air resistance.</p> Signup and view all the answers

    How is the tractive effort (TE) required to start a train calculated?

    <p>By summing the resistance of the load, loco, and train weights.</p> Signup and view all the answers

    What does the variable 'a' represent in the train resistance formula?

    <p>Static friction.</p> Signup and view all the answers

    Which of the following is NOT a factor contributing to train resistance during a run?

    <p>Resistance due to atmospheric pressure.</p> Signup and view all the answers

    Which of these states accounts for resistance to start a train on straight level track?

    <p>Static resistance.</p> Signup and view all the answers

    If the drag of the train increases with speed, what effect does this have on the effective torque?

    <p>It decreases the effective torque.</p> Signup and view all the answers

    What does 'TE' stand for in the context of train operation?

    <p>Tractive Effort.</p> Signup and view all the answers

    What happens to the balancing speed of a train on an up-gradient compared to level ground?

    <p>It decreases.</p> Signup and view all the answers

    How is the tractive effort required to overcome curve-resistance determined?

    <p>By weight and speed of the train.</p> Signup and view all the answers

    What is the effect of increasing gear ratio on a locomotive's performance?

    <p>It allows for higher starting tractive effort.</p> Signup and view all the answers

    What change occurs in tractive effort as wheel diameter decreases?

    <p>Starting tractive effort increases.</p> Signup and view all the answers

    How does field shunting affect a DC motor's operation?

    <p>It enables the motor to run faster than its balancing speed.</p> Signup and view all the answers

    What is the formula for calculating the running resistance of a train at a given speed 'V' for a BOXN load?

    <p>T1 = 0.6438797 + 0.01047218 V + 0.00007323 V²</p> Signup and view all the answers

    How does the gravitational force acting on a 150 tonne train calculate?

    <p>Force = 150 x 1000 x 9.8</p> Signup and view all the answers

    What is the resistance due to gravity for a train on a gradient of 1 in 200?

    <p>7.3575 kN</p> Signup and view all the answers

    For a given gradient 'G', how is Specific Grade Resistance expressed?

    <p>Specific Grade Resistance = (1/G) in kg/t</p> Signup and view all the answers

    What components remain unchanged when calculating running resistance of a train as it runs?

    <p>T3 and T4</p> Signup and view all the answers

    What is the effective voltage governed by in relation to train drag and resistance?

    <p>By the torque of the motor</p> Signup and view all the answers

    What happens when the train starts to climb a grade and the speed reduces?

    <p>Back voltage increases</p> Signup and view all the answers

    Which of the following correctly describes the relationship between Tractive Effort (TE) and overall train resistance?

    <p>TE must be greater than overall train resistance to accelerate</p> Signup and view all the answers

    What modifies the effective voltage available to the motor during train operation?

    <p>The drag force acting against the train</p> Signup and view all the answers

    What is the starting resistance of a loco expressed in kg/ton?

    <p>6 kg/ton</p> Signup and view all the answers

    What happens to the tractive effort as speed increases beyond the 20 mph mark?

    <p>Tractive effort falls as speed increases.</p> Signup and view all the answers

    How is power calculated when given a force and speed?

    <p>Power = Force x Speed</p> Signup and view all the answers

    Which of the following best describes the relationship between mass, acceleration, and tractive effort?

    <p>Tractive effort is directly proportional to mass and acceleration.</p> Signup and view all the answers

    At what point does maximum tractive effort occur based on the content?

    <p>Between speeds of 0 and 20 mph.</p> Signup and view all the answers

    How is energy defined in the context of moving an object?

    <p>Energy is the product of force and distance.</p> Signup and view all the answers

    What unit is used to express the maximum tractive effort in the example provided?

    <p>kN</p> Signup and view all the answers

    Which statement correctly describes the relationship of speed and power at the rail?

    <p>Power is the product of force and speed, limited by tractive effort.</p> Signup and view all the answers

    What happens to acceleration when tractive effort decreases with increasing speed?

    <p>Acceleration decreases, leading to slower speed buildup.</p> Signup and view all the answers

    How does a reduction in gear ratio affect the locomotive's operational characteristics?

    <p>Increases starting torque while reducing maximum operational speed.</p> Signup and view all the answers

    What is the impact of wheel diameter reduction on tractive effort at different speeds?

    <p>Increases tractive effort at lower speeds but reduces it at higher speeds.</p> Signup and view all the answers

    Which statement accurately describes the effect of field shunting on a DC motor's operation?

    <p>Weakens the motor field, allowing for increased speed at the expense of torque.</p> Signup and view all the answers

    What occurs to the torque as the motor accelerates and the internally generated voltage increases?

    <p>Torque decreases due to reduced current.</p> Signup and view all the answers

    Which statement best defines the balancing condition for a train?

    <p>It is when the torque produced matches the train’s resistance.</p> Signup and view all the answers

    What is the significance of curvature resistance calculated using the formula TC = 0.4 X S X W?

    <p>It indicates the resistance force acting against the forward motion of the train on a curve.</p> Signup and view all the answers

    How does one define Continuous Tractive Effort in relation to train operation?

    <p>The tractive effort required to maintain train motion consistently without slipping.</p> Signup and view all the answers

    In the formula for train resistance, what does the variable 'b' specifically represent?

    <p>Resistance due to mechanical factors.</p> Signup and view all the answers

    What specifically does a gearbox do in relation to the traction motors and train axles?

    <p>Adjusts the motor speed to match the required axle speed for effective traction.</p> Signup and view all the answers

    What primarily affects the Continuous Power rating of equipment?

    <p>The equipment characteristic and operational assumptions.</p> Signup and view all the answers

    What is the principal component expressed by 'a' in the train resistance formula?

    <p>Static friction while starting the train.</p> Signup and view all the answers

    How is the effective voltage available to the motor primarily determined?

    <p>By the resistance offered by the train.</p> Signup and view all the answers

    What limits the Short Term Tractive Effort when attempting to climb a grade?

    <p>Overheating of traction motors and transmission equipment.</p> Signup and view all the answers

    Which of the following statements best describes Maximum Power at Rail?

    <p>It represents the peak power needed for train acceleration.</p> Signup and view all the answers

    Which scenario best describes the impact of increasing the motor notches?

    <p>It temporarily increases effective voltage and torque.</p> Signup and view all the answers

    What does the term 'cv^2' in the train resistance formula indicate?

    <p>Air resistance proportional to the square of speed.</p> Signup and view all the answers

    What is the relationship between starting tractive effort and the locomotive's weight?

    <p>Starting tractive effort is proportional to the loco weight multiplied by adhesion.</p> Signup and view all the answers

    Which statement accurately describes the existence of train resistance?

    <p>It applies regardless of speed or gradient.</p> Signup and view all the answers

    What happens to the power curve of the equipment at speeds exceeding 70 mph?

    <p>It shows a dip indicating decreased efficiency.</p> Signup and view all the answers

    What does 'back emf' in a DC motor primarily counteract during operation?

    <p>The externally applied voltage.</p> Signup and view all the answers

    What is the influence of gradient on train resistance according to the context?

    <p>Gradient contributes additional resistance when climbing uphill.</p> Signup and view all the answers

    Which of the following statements is true regarding the tractive effort required to start a train?

    <p>It varies based on the operational gradient and curvature.</p> Signup and view all the answers

    Which parameter is NOT included when computing Tractive Effort?

    <p>Speed of the train</p> Signup and view all the answers

    What is primarily considered when estimating Continuous Power in traction systems?

    <p>The time spent coasting at lower tractive efforts.</p> Signup and view all the answers

    What effect does the increase in speed generally have on tractive effort needed?

    <p>Tractive effort may increase due to resistance.</p> Signup and view all the answers

    What is the formula used to calculate the running resistance of a train at speed 'V' for a locomotive?

    <p>T1 = 0.6438797 + 0.01047218 V + 0.00007323 V2</p> Signup and view all the answers

    How is the tractive effort (TE) required to overcome a gradient of '1 in G' calculated for a train of weight 'W'?

    <p>TG = W / G</p> Signup and view all the answers

    What is the approximate gravitational force acting on a 150 tonne train?

    <p>1,471,500 N</p> Signup and view all the answers

    If a train climbs a 1 in 200 gradient, what is the resistance due to gravity?

    <p>7.3575 kN</p> Signup and view all the answers

    For a loco, how is the second term of the running resistance formula influenced during operation?

    <p>It increases linearly with speed.</p> Signup and view all the answers

    What component remains unchanged when calculating the running resistance of a train at a constant speed?

    <p>Curve Resistance (T4)</p> Signup and view all the answers

    Which term in calculating running resistance describes the contribution of speed squared?

    <p>0.00007323 V2</p> Signup and view all the answers

    When speed reduces due to a train climbing a grade, what effect does this have on the back voltage?

    <p>The back voltage decreases.</p> Signup and view all the answers

    What is the term used to describe the resistance experienced by a train moving on a gradient of '1 in 1'?

    <p>Full Gravitational Resistance</p> Signup and view all the answers

    Study Notes

    Tractive Effort and Train Resistance

    • Force and Acceleration: Applying force to a mass causes acceleration, following Newton's laws of motion. Force equals mass times acceleration.
    • Tractive Effort (TE): The force applied to the train's wheels to cause movement. It's determined by the power equipment and driver control.
    • Energy: Energy used to move an object over a distance is the product of force and distance.
    • Power: Power is the rate of energy usage or energy per unit time. Power equals force times speed or energy divided by time.
    • Power and Speed: Tractive effort varies with speed. At speeds below 20mph, TE is constant, leading to constant acceleration. Above that speed, TE reduces, resulting in decreasing acceleration and a curved speed-time relationship. This is limited by the maximum adhesion between wheels and rails. Maximum Tractive Effort is the maximum TE that can be applied.
    • Maximum Power at Rail: Maximum power at the rail corresponds to the maximum TE (100 kN in example) multiplied by speed = 100kN x (20mph/2.2ms⁻¹)=910 kW
    • Train Resistance: Resistance encountered by the train, increasing with speed. It's calculated as a + bv + cv². Factors include static friction, mechanical factors and air resistance.
    • Types of Tractive Effort: -Starting Tractive Effort: Force needed to start a stationary train without wheel slip. -Continuous Tractive Effort: Force needed to keep a train moving continuously without wheel slip. -Short Term Tractive Effort: Force needed for short durations, such as climbing a grade (up to 120% of continuous TE).
    • Effect of Gradient: Gradients affect train resistance; the greater the incline (gradient), the higher the resistance. Resistance (TG= W/G) where W is train weight and G is the gradient.
    • Effect of Curve: Curves induce resistance (given by Tc=0.4 * S * W)
    • Gear Ratio: Gear ratio affects the minimum and maximum speeds at which the train operates safely.
    • Wheel Diameter: Smaller wheel diameters have higher starting tractive effort but lower high-speed tractive effort.
    • Field Shunt: The current through the field coils of a DC motor is reduced by increasing the resistance, allowing the train to speed up, however, the power decreases.

    Additional Points

    • Speed vs. Time curves illustrate how speed changes over time based on acceleration or deceleration.
    • Power vs. Speed graphs display the relationship between power output and train speed.
    • Balancing conditions are the point where tractive effort equals train resistance, allowing for a constant speed.

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    Description

    This quiz explores the concepts of tractive effort and train resistance in the context of physics and engineering. You will learn how force, power, and acceleration interact in the movement of trains, following the principles laid out by Newton's laws. Understanding these elements is crucial for comprehending the dynamics of train performance.

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