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Interactive Audio Lesson
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Understanding Rolling Resistance
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Today, we'll discuss rolling resistance. Can anyone tell me how we might calculate it from a vehicle's weight?
We can convert the weight from kilograms to tons.
Excellent! For instance, if the gross weight of a machine is 50,000 kg, how many tons is that?
That would be 50 tons.
Correct! Now, if the rolling resistance is 28 kg per ton, what would the total rolling resistance be?
It would be 1400 kg, right? Because 50 tons times 28 kg is 1400 kg.
Exactly! Rolling resistance is a critical factor in our calculations.
Remember the acronym ROLL: Resistance, Overcome, Load, Lift, to help remember this concept.
Total Resistance Calculation
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Now, let's calculate the total resistance. We already know our rolling resistance is 1400 kg. What about penetration resistance?
Isn't it based on how deep the tire sinks into the ground?
Exactly! Here, if the tire sinks 6 cm and it's 6 kg per ton per centimeter, how do we calculate that?
We'd multiply 6 kg by 6 cm and then by the 50 tons!
Perfect! That gives us a penetration resistance of 1800 kg. So, how do we find the total resistance?
We add the rolling resistance and penetration resistance together!
Correct! The total resistance is 3200 kg, which is crucial for understanding the power needed.
Grade Resistance Overview
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Next, let's discuss grade resistance, which occurs when machines climb slopes. Why do we need more power for this?
Because the machine is working against gravity!
Exactly! The steepness of the slope impacts how much tractive effort is required. Who remembers how that’s quantified?
Each percent of slope requires an additional 10 kg per ton of machine weight.
Right! If we have a slope of 5%, how much extra power do we need for a 50-ton machine?
That would be 5 times 10 kg per ton times 50 tons, which equals 2500 kg!
Great job! Remember that better routes can minimize this resistance and save cost.
Available vs Usable Power
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Let's now discuss available power. What do we mean by this term?
It's the power the manufacturer states for a machine?
Exactly! However, this becomes usable power based on project conditions. Can anyone explain how these conditions affect usable power?
Factors like altitude and temperature can lower the effectiveness of that power.
Correct! With higher altitudes, engine performance drops due to lower atmospheric pressure. How can we calculate usable power?
By subtracting the power needed for resistances from the total available power!
Exactly! That’s the key to understanding how much power is really available for work.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
In this section, we discuss the calculation of rolling resistance, penetration resistance, and grade resistance that affect the tractive effort required from a machine. We also explore the distinction between available power and usable power, emphasizing the significance of these calculations in the context of selecting appropriate machinery for specific tasks.
Detailed
In this section, we delve into the nuances of determining available power for machinery operating under varied conditions. We start by converting vehicle weights from kilograms to tons, allowing easier calculation of rolling resistance, typically measured in kilograms per ton. The gross weight of the machine (50 tons) is multiplied by the rolling resistance value (28 kg per ton) to yield a total rolling resistance of 1400 kg. Next, we calculate penetration resistance based on the depth of tire classification (6 cm), resulting in additional resistance of 1800 kg. When both resistances are summed, the total resistance is identified at 3200 kg, indicating the minimum tractive effort necessary to overcome these forces.
Continuing, we differentiate between grade resistance and grade assistance—grades influence how much power must be exerted to climb or descend slopes. By examining the slope’s percentage, the tractive effort needed is adjusted, illustrating the importance of considering terrain in machinery selection. Grade resistance is quantified using the manageable formula where each 1% of grade results in a requirement of 10 kg per ton of machine weight. This section concludes by examining the 'usable power,' defined as the power available for actual work after overcoming resistance, emphasizing project conditions like altitude and temperature as key indicators of how much of the available power a machine can actually utilize.
Audio Book
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Weight Conversion to Tons
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So, let us convert the vehicle weight into tons, because your rolling resistance is commonly expressed as kg per ton. So, let us convert the weight of the machine into tons you know that the gross weight of the machine is given as 50,000 kg. So, 1000 kg = 1 ton, so divided you will get the gross weight of the machine as 50 tons.
Detailed Explanation
To work with rolling resistance, we first need to convert the weight of the vehicle from kilograms to tons. Since 1 ton equals 1,000 kg, we can convert the gross weight of the machine (50,000 kg) into tons by dividing it by 1,000. Therefore, the gross weight in tons is 50 tons.
Examples & Analogies
Think of it like converting a distance from meters to kilometers. If you live 5,000 meters away from school, you can easily say you live 5 kilometers away by dividing by 1,000. Similarly, converting vehicle weight helps us use a standard measure that is often easier to work with.
Calculating Rolling Resistance
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Now, the rolling resistance you need to calculate for this particular haul route it is given as 28 kg per ton. So, you multiply the gross weight of the machine by the rolling resistance value. So, gross weight is 50 tons multiplied by the rolling resistance is 28 kg per ton for that particular haul route. So, now we are going to calculate for your particular vehicle what is the total rolling resistance? That is nothing but 1400 kg, so 1400 kg is your rolling resistance.
Detailed Explanation
To find the rolling resistance, we take the gross weight in tons (50 tons) and multiply it by the rolling resistance value, which is 28 kg per ton. This calculation gives us the total rolling resistance of the vehicle: 50 tons × 28 kg/ton = 1400 kg.
Examples & Analogies
Imagine pushing a heavy box on the floor. The heavier the box, the more force you need to use to push it. In this case, the 'box' is the vehicle, and the 'force' is the rolling resistance. The rolling resistance represents the extra effort needed just to keep moving, based on the vehicle's weight.
Determining Penetration Resistance
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Now we need to find the penetration resistance. It is given to you in the problem that the tyre is sinking to the depth of 6 centimeters into the surface. So, you know that for each centimeter of penetration the amount of effort needed is 6 kg per ton per centimeter you know that. So, you multiply that by how much is the depth of penetration? It is nothing but 6 centimeters, and what is the gross weight of the machine? It is nothing but 50 tons. So, that gives you the penetration resistance as 1800 kg.
Detailed Explanation
Penetration resistance relates to how much weight the tire sinks into the surface. For every centimeter of penetration, the machine requires an effort of 6 kg per ton. With 6 centimeters of penetration and a gross weight of 50 tons, we calculate the penetration resistance: 6 cm × 6 kg/ton/cm × 50 tons = 1800 kg.
Examples & Analogies
Think about wading in mud. The deeper you step in, the harder it is to lift your feet out. Similarly, penetration resistance accounts for the added effort needed due to how deeply the tires sink into soft surfaces.
Total Resistance Calculation
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Now we can find the total resistance, that is nothing but add your rolling resistance and the penetration resistance. It is nothing but your 1400 kg + 1800 kg, so that gives me the answer as 3200 kg is the total resistance.
Detailed Explanation
To find the total resistance the vehicle faces, we simply add the rolling resistance and the penetration resistance together. So, 1400 kg (rolling) + 1800 kg (penetration) = 3200 kg, which is the total force the machine needs to overcome during movement.
Examples & Analogies
Imagine carrying two bags of groceries, one weighing 1.4 kg and the other 1.8 kg. If you're asked to carry both, you would simply add their weights together to find the total weight you have to lift. Similarly, calculating total resistance integrates different opposing forces.
Determining Tractive Effort
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So, I need tractive effort of at least 3200 kg to overcome this resistance in a project site. So, the total tractive effort needed to overcome this resistance is 3200 kg. So, select the machine accordingly, that is the purpose of estimating all this resistance, so that we can know what is the required power for your machine?
Detailed Explanation
Tractive effort is the force needed by the vehicle to overcome resistance and move forward. In this case, we determined that 3200 kg of tractive effort is required to push through the identified resistances, thus informing our choice of machinery based on its capability to provide this force.
Examples & Analogies
Think of it like planning a trip uphill with your bicycle. If the hill is steep (i.e., high resistance), you need a stronger bike or more energy to pedal. Identifying the necessary tractive effort helps you choose the right 'bike' (machine) to complete your task effectively.
Understanding Grade Resistance
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Now so far, we have discussed about the rolling resistance, let us look into the other part of the resistance in your project site that is your grade resistance. Most often you can see that equipment has to climb up a slope. So, when the machine is climbing up the slope, obviously you need some additional efforts to make it move up the slope because it is pulling against the gravity.
Detailed Explanation
Grade resistance refers to the additional effort required when a machine must ascend a slope. As the steepness of the slope increases, so does the grade resistance, as the vehicle needs to exert more force to work against gravity.
Examples & Analogies
Consider walking uphill versus walking on a flat surface. It takes more effort to climb a hill because you are working against gravity. Similarly, machines deal with this extra effort when they have to move up a slope, which contributes to the total resistance they face.
Grade Assistance
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Now similar to this, we should also know about what is grade assistance? So, we discussed about what is grade resistance, there is something called as grade assistance that means what? When your machine is moving down the slope, you can see that the amount of power needed gets reduced because it can easily move down by the gravity, so the gravitational force will help you to easily move the machine.
Detailed Explanation
Grade assistance is the opposite of grade resistance. When a machine descends a slope, gravity assists its movement. This results in reduced power requirements compared to climbing uphill. Understanding grade assistance can influence decisions on machine use based on the terrain.
Examples & Analogies
Riding a bicycle downhill is much easier than going uphill. You naturally move faster with less effort while descending due to gravity. This concept helps to understand how machines can benefit from downhill movements, reducing energy use significantly.
Calculating Grade Resistance
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Grade resistance is nothing but by simple elementary mechanics people have worked out this relations. ... So, for every 1% of grade, so your grade resistance is 10 kg per ton.
Detailed Explanation
To calculate grade resistance, we utilize a basic guideline where 1% of a slope requires 10 kg of force for every ton of weight. This serves as a method for estimating how much additional tractive effort is necessary when moving uphill.
Examples & Analogies
If you're hiking up a hill with a 5% grade, each step requires effort. Just as we relate effort to the steepness of a hike, machines relate grade percentages to the additional force needed to move loads up slopes.
Equivalent Gradient Calculation
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You can convert a rolling resistance also into equivalent gradient. The rolling resistance which you have expressed in kg per ton, that you can converted into gradient percentage equivalent gradient I can convert it...
Detailed Explanation
Rolling resistance values, often shown as kg per ton, can be converted into an equivalent gradient percentage. By understanding both formats, it becomes easier to assess the overall impact of both rolling and grade resistances on machine performance.
Examples & Analogies
Think of how distances can be represented in different units (like miles vs kilometers). Just as this makes distance more manageable in travel plans, converting resistance values aids in assessing machine capabilities on varying terrains.
Usable Power Estimation
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So far what we have discussed is about the required power. So, what is the total power required by the machine to overcome the different resistances in the project site...
Detailed Explanation
After determining all necessary resistances, we now focus on how much power the machinery can actually provide, termed as usable power. This involves understanding the power rating given by manufacturers and the impacts of site conditions on actual power delivery.
Examples & Analogies
Consider a smartphone with a battery life of 12 hours according to specifications. However, in real-world usage (like gaming), that battery power may last only 6 hours. Like the smartphone’s usage scenario, a machine's power rating may differ when applied to real conditions.
Determining Usable Power
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Now let us see what is this usable power? ... which can be realized at the point of contact between the tire and the ground, this is what is of our major interest?
Detailed Explanation
Usable power refers to the effective power available for tasks after deducting power used to overcome resistances. This measurement is crucial for determining if machinery can perform the required work in a given scenario.
Examples & Analogies
Consider a train that has a total power output but uses a portion of that power to overcome friction on the tracks. The remaining power can be used to pull freight. Understanding this gives insights into how much load can be carried.
Calculating Rimpull
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The usable power you can express in terms of rimpull or drawbar pull. ... So, the usable tractive force developed at the point of contact between the tyre and the ground is called as a rimpull.
Detailed Explanation
Rimpull refers to the tractive effort available at the tires of a wheeled vehicle. Understanding rimpull allows us to assess how well a vehicle can perform tasks, as it accounts for contact and traction between the tires and the ground, essential for effective operation.
Examples & Analogies
Think of rimpull like the grip of your shoe on the ground when you run. If you have excellent grip, you're more likely to run faster and jump higher, versus slipping on a wet surface. Rimpull helps predict how well machinery can operate on different terrains.
Factors Affecting Usable Force
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So, another important thing to be noted is weight on the power running gear of the machine. ... So, usable force is nothing but weight on the power running gear multiplied by the coefficient of traction of the travel surface.
Detailed Explanation
Various factors influence how much usable force a machine can produce, primarily the weight over the driving gears and the traction coefficient of the surface. Understanding the relationship allows for better efficiency and effective power use in operation.
Examples & Analogies
Imagine how much better a heavy truck can grip a wet road compared to a light bicycle. Just like the weight of the truck can enhance grip, the weight on a vehicle’s wheels influences its ability to generate usable force effectively.
Usable Force and Horsepower Relationship
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If you have sufficient grip sufficient traction between the tire and the ground...If the traction is sufficient, you can take the rimpull as a direct function of the horsepower of the machine.
Detailed Explanation
When traction between tires and ground is optimal, we can directly relate usable force (rimpull) to horsepower. Thus, knowing machine specifications aids in calculating how much effective force is available during operation.
Examples & Analogies
Again, think of a race car. If it has enough grip and is equipped with a powerful engine, it can accelerate smoothly and maintain high speeds. Traction translates horsepower into real usable force on the race track.
Practical Calculation Example
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Now let us workout the problem on how to estimate the power requirements of the machine. ... So, out of this 7000 kg, 1500 kg will be used for overcoming the resistances.
Detailed Explanation
Engaging in a practical example helps emphasize the concepts of power requirements and resistance calculations. Breaking down values confirms understanding and indicates the power available for actual work after resistances.
Examples & Analogies
If you work part-time and earn $700, but have $150 in expenses, the amount you actually save and can use is $550—a direct reflection of understanding total income vs. value spent on necessary applied forces in a work scenario.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Rolling Resistance: The resistance experienced by vehicles due to weight and surface interaction.
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Penetration Resistance: Resistance due to tire sinking into the ground, based on depth.
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Grade Resistance: Force required to overcome the effects of gravity on slopes.
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Total Resistance: The sum of both rolling and penetration resistance.
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Available Power: Power rated by manufacturers under defined standard conditions.
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Usable Power: The effective power available after accounting for resistance forces.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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If a vehicle has a gross weight of 50 tons and a rolling resistance of 28 kg per ton, the rolling resistance would be 1400 kg.
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When climbing a 4% slope, the grade resistance can be calculated as 10 kg per ton, leading to a total grade resistance of 600 kg for a 15-ton vehicle.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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To roll and climb, do calculate; resistance you must never hate.
📖 Fascinating Stories
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Imagine a heavy truck named Tread. Tread had to roll over muddy ground and steep hills. Each time he tackled a hill, he learned to calculate his rolling and grade resistance to keep moving forward.
🧠 Other Memory Gems
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Remember the acronym RAMP: Resistance, Altitude, Machines, Power. It will help you recall the key aspects of determining usable power.
🎯 Super Acronyms
G.R.A.D.E.
- Grade Resistance And Driving Effort helps understand the concept of how slope affects power.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Rolling Resistance
Definition:
The resistance a vehicle encounters when moving over a surface due to its weight and surface interaction.
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Term: Penetration Resistance
Definition:
Resistance caused by a tire sinking into the ground, requiring additional tractive effort.
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Term: Grade Resistance
Definition:
The additional force required to move up or down a slope due to gravity.
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Term: Usable Power
Definition:
The amount of power available for actual work after accounting for resistances.
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Term: Available Power
Definition:
The power rating provided by the manufacturer under standard conditions.