# What is the relationship between weight of car, power needed and speed

• Maxicl
In summary, the conversation discusses the factors that affect the energy efficiency and time efficiency of different delivery methods. These factors include weight and speed of the vehicle, as well as the presence of hills and regenerative braking. There is also a mention of the relationship between these factors and how it differs between vans, cars, and bikes. The main question behind the project is to determine the most optimal network for energy and time efficiency. The conversation also includes a suggestion to come up with equations to calculate the energy and person-hours used in each option.

#### Maxicl

TL;DR Summary
Hi, I'm working on a project to see if deliveries, pick ups, or both combined are better for the environment / more energy efficient / more time efficient.
For example, (a) everyone collecting from a farm by bike, (b) vans bringing to supermarkets and then people collecting from supermarkets, or (c) vans -> town depot -> home delivery.

Does the power usage of the van depend on how much weight it is carrying? What about the speed? And what is the relationship between these?
Hi, I'm working on a project to see if deliveries, pick ups, or both combined are better for the environment / more energy efficient / more time efficient. For example, (a) everyone collecting from a farm by bike, (b) vans bringing to supermarkets and then people collecting from supermarkets, or (c) vans -> town depot -> home delivery.
Does the power usage of the van depend on how much weight it is carrying? What about the speed? And what is the relationship between these?
Is the relationship different for vans/cars/bikes?

The main question behind this is what sort of network would be most optimised for energy and what would be most optimised for time, but I am just trying to build up intuition towards this. Would be glad if anyone can help or direct me :)

Welcome to PF.

Maxicl said:
Does the power usage of the van depend on how much weight it is carrying? What about the speed?
That will depend on if there are hills, and if the van has regenerative braking.
Bicycles are not easy to ride up hills.
Vehicles must accelerate to get moving, then to stop they convert kinetic energy to heat in the brakes.
At higher speeds vehicle air drag increases as the square of velocity.
The load will weigh about the same as the tare of the van. An almost empty van costs fuel and a driver's wages.

Welcome to PF.

I'm sure you drive a car. Doesn't your gas mileage go down when you drive faster? Does a dump truck full of dirt use more fuel than your VW?

Yes, both speed and weight matter. The problem is calculating how much they vary without specific knowledge about the vehicles. You might best guess at the parameters for your study. Then re-run the simulation for the extreme ranges of your guesses. That will at least provide a range of results.

Welcome to PF.
Maxicl said:
I'm working on a project
Is this a schoolwork project? If so, I can move this thread to the schoolwork forums for you.

Maxicl said:
The main question behind this is what sort of network would be most optimised for energy and what would be most optimised for time
Start to come up with a framework of equations for each (energy used and person-hours used) for each of the steps and options you've outlined. The equations don't have to be exact yet, but as you start to outline them you will start to see what considerations you need to include.

Baluncore said:
Welcome to PF.That will depend on if there are hills, and if the van has regenerative braking.
Bicycles are not easy to ride up hills.
Vehicles must accelerate to get moving, then to stop they convert kinetic energy to heat in the brakes.
At higher speeds vehicle air drag increases as the square of velocity.
The load will weigh about the same as the tare of the van. An almost empty van costs fuel and a driver's wages.

Thank you!

berkeman said:
Welcome to PF.

Is this a schoolwork project? If so, I can move this thread to the schoolwork forums for you.Start to come up with a framework of equations for each (energy used and person-hours used) for each of the steps and options you've outlined. The equations don't have to be exact yet, but as you start to outline them you will start to see what considerations you need to include.
No, just my own.
Ok, I've made some formulas now, but not sure about the E=Fd rule... If I've made formulas for forces due to friction and know instantaneous acceleration of the vehicle, is calculating energy just a matter of E= (ForceFriction - Mass*Acceleration)*distance ?
Thank you!

anorlunda said:
Welcome to PF.

I'm sure you drive a car. Doesn't your gas mileage go down when you drive faster? Does a dump truck full of dirt use more fuel than your VW?

Yes, both speed and weight matter. The problem is calculating how much they vary without specific knowledge about the vehicles. You might best guess at the parameters for your study. Then re-run the simulation for the extreme ranges of your guesses. That will at least provide a range of results.
Mmm, I guess I might need to look at different car specs ... I've also read there's different power efficiencies depending on the gear you use so that may also come into it.
Thank you!

Maxicl said:
is calculating energy just a matter of E= (ForceFriction - Mass*Acceleration)*distance ?
Yes, it is.

I'm not sure what you mean by "ForceFriction", but there are no subtractions. All the forces implied are added up and they are rolling resistance, aerodynamic drag, and inertia (mass*acceleration).

The rolling resistance is usually minor and the aerodynamic drag is more significant on the highway (constant high speed) and inertia is more significant in the city (frequent accelerations, but low speed).

Ranger Mike