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A short class with Sarah and her students. The other ways are under More.
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Today, we will discuss how we calculate rolling resistance for vehicles. Rolling resistance is typically expressed in kilograms per ton. Can anyone tell me how we can convert vehicle weight into tons?
We need to divide the weight in kilograms by 1,000.
Correct! If a vehicle weighs 50,000 kg, what would that be in tons?
That would be 50 tons!
Exactly. Now, if the rolling resistance is 28 kg per ton, how do we find the total rolling resistance for our vehicle?
We multiply the gross weight in tons by the rolling resistance value.
Great! So, what is the total rolling resistance for a 50-ton vehicle?
It would be 1,400 kg!
Correct! Remember, rolling resistance is crucial to determine the effort required to move a vehicle. Let's summarize this part: we convert weight to tons and then multiply by the rolling resistance to find the total.
Next, let's talk about penetration resistance. If a tire sinks 6 centimeters into the surface, how do we calculate the penetration resistance?
We multiply the depth of penetration by 6 kg per ton.
Correct! Based on our previous example of a vehicle weighing 50 tons, what would the penetration resistance be?
It would be 1,800 kg!
Exactly right! Now, how do we find the total resistance when we combine rolling and penetration resistance?
We simply add both resistances together.
Correct! For our calculations, what is the total resistance?
It would be 3,200 kg!
Excellent! So the total resistance directly informs the power we'll need for our machine.
Now, let's explore grade resistance. What happens when a vehicle moves uphill?
It needs extra effort to overcome the gravitational pull.
Exactly! The steeper the slope, the greater the grade resistance. What do we know about calculating grade resistance on a 1% slope?
It's 10 kg per ton!
Great! Using that, how much effort do we need to overcome a 4% grade for a 15-ton vehicle?
We would multiply 4% by 10 kg per ton and then by 15 tons.
Exactly! What would the grade resistance be?
It would be 600 kg!
That's right! Grade resistance is a key factor to consider for equipment operation, along with rolling resistance.
It is derived from the weight of the vehicle and the surface type, influencing the energy required for mobility.
Additional energy required to overcome gravitational forces while ascending slopes, directly related to the steepness of the incline.
The sum of rolling resistance and penetration resistance that must be overcome to maintain vehicular movement.
To find rolling resistance, don't be shy, divide by a thousand, give it a try.
Imagine a truck named Tommy that weighed 50 tons. Every time it rolled over a road, it had to push against a force named 'Rolling.' Tommy learned that every hill made him work even harder, needing extra energy based on how steep the hill was.
RPG: Resistance Comes from Penetration and Grade! Use this to remember that rolling resistance and penetration affect total movement.
RICE: Remember, it's Calculations for Effort! This helps to recall how to calculate total resistance.
Term
What is rolling resistance?
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Term
What does grade resistance indicate?
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How is total resistance calculated?
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The force that opposes the motion of a vehicle when tires roll over a surface, usually measured in kilograms per ton.
The resistance faced when tires sink into the surface, calculated based on how deep the tires penetrate.
The extra force needed to move a vehicle up an incline, which increases with the steepness of the slope.
The force required to move a vehicle forward, overcoming resistance.
The load carried by a vehicle, including both the cargo and the weight of the vehicle itself.
This section explains how to calculate rolling resistance and grade resistance for moving vehicles, emphasizing their significance in determining the required power for machines on varying slopes.
The section details the calculation of rolling resistance based on vehicle weight and the specifics of the haul route, alongside insights into grade resistance that occurs when climbing or descending slopes. It illustrates the importance of understanding these resistances to select equipment that can effectively manage the associated power requirements.
This section focuses on the critical calculations for determining rolling resistance and grade resistance, which are vital for understanding the power requirements of vehicles operating on various terrains.
Rolling Resistance Calculation: The section begins by converting vehicle weight from kilograms to tons, using a vehicle weight of 50,000 kg, equivalent to 50 tons. The rolling resistance for this machine is identified as 28 kg per ton, leading to a rolling resistance of 1,400 kg (50 tons x 28 kg/ton).
Penetration Resistance: Additionally, if a tire penetrates the surface by 6 centimeters, the calculation for penetration resistance involves multiplying this depth by 6 kg per ton per centimeter, resulting in 1,800 kg of penetration resistance.
Total Resistance: The total resistance, which combines rolling and penetration resistance, here amounts to 3,200 kg, representing the tractive effort required for the machine to operate efficiently in project conditions.
The section also discusses grade resistance—an additional force that opposes the movement of a vehicle on slopes. The tractive effort needed to overcome this resistance varies with the slope percentage, establishing that a steeper slope increases resistance.
The section emphasizes calculating grade resistance (10 kg per ton for a 1% slope), noting the importance of optimal haul route selection to minimize overall resistance and operating costs. The relationship between rolling resistance and equivalent gradients is also highlighted, enabling better assessment of total resistance dynamics.
In conclusion, this section illustrates the essential calculations necessary for estimating power requirements for vehicles, providing both theoretical and practical applications for road construction and other similar fields.