How much force does a moving car exert on to the road?

[MustafaTekinay]

Homework Statement

Does a faster car exert less force on the ground at a given point and a given time compared to a slower one? Do the slower moving cars cause more peak strain value at a given point on the road?

Relevant Equations

F=ma

I understand that the weight of the car does not change (assuming mass of the car stays the same) because of f=mg. But I am not so sure about of the aerodynamics of the car plays a role. Say, a faster car might have more air under their wheels and might exert less force on to the ground. Maybe a faster car exerts less force on to the ground because of the time it takes the weight of the car to transfer to the ground.

Thanks for the help.

 

[jack action]

The car can be viewed as a wing and can generate an aerodynamic lift force or a downforce that is added to (or subtracted from) the total weight of the car. Typical road cars generate a lift force, but racing cars most likely generate a downforce by design.

Also, during acceleration or braking (independent of speed), there will be a weight transfer between the front and rear axles. This doesn't modify the total force due to the weight of the car, but it modifies the weight distribution between the two axles. The same thing happens with the lateral acceleration and the right & left wheels weight distribution.

 

[jackwhirl]

Homework Statement:: Does a faster car exert less force on the ground at a given point and a given time compared to a slower one? Do the slower moving cars cause more peak strain value at a given point on the road?

Have you copied the homework statement exactly?

 

[jbriggs444]

Do the slower moving cars cause more peak strain value at a given point on the road?

A literal and careful reading of the phrase "peak strain value" would mean peak deflection of the road surface under the force of the car's tires. So one would want to think about the behavior of the road surface over time.

I would not try to bring aerodynamics into the question. Adding complications will not simplify things.

 

[Lnewqban]

... Maybe a faster car exerts less force on to the ground because of the time it takes the weight of the car to transfer to the ground.

That is an incorrect assumption.
Is the problem referring to straight trajectory, cornering or both?

 

[MustafaTekinay]

The car can be viewed as a wing and can generate an aerodynamic lift force or a downforce that is added to (or subtracted from) the total weight of the car. Typical road cars generate a lift force, but racing cars most likely generate a downforce by design.

Also, during acceleration or braking (independent of speed), there will be a weight transfer between the front and rear axles. This doesn't modify the total force due to the weight of the car, but it modifies the weight distribution between the two axles. The same thing happens with the lateral acceleration and the right & left wheels weight distribution.

Thanks for the reply. So for typical cars, the strain will be less?

 

[MustafaTekinay]

Have you copied the homework statement exactly?

Thanks for the reply. Not word by word but the question is the same.

 

[MustafaTekinay]

A literal and careful reading of the phrase "peak strain value" would mean peak deflection of the road surface under the force of the car's tires. So one would want to think about the behavior of the road surface over time.

I would not try to bring aerodynamics into the question. Adding complications will not simplify things.

Thanks for the reply. Would not aerodynamics play a role in the amount of force the wheels exert on the ground. If the car is flying over the road, then there would not be (almost) no force exerted on the ground.

 

[MustafaTekinay]

That is an incorrect assumption.
Is the problem referring to straight trajectory, cornering or both?

Thanks for the reply. Imagine a road and a vehicle at a constant speed traveling in a straight trajectory. Would the tires cause more stress or strain on the ground if moving slower?

 

[haruspex]

Thanks for the reply. Would not aerodynamics play a role in the amount of force the wheels exert on the ground. If the car is flying over the road, then there would not be (almost) no force exerted on the ground.

The aerodynamics can act either way. High performance cars have inverted aerofoils to press them down onto the road for better roadholding. Even a regular passenger car would not be designed so as to lose traction at high speed.

 

[Lnewqban]

Thanks for the reply. Imagine a road and a vehicle at a constant speed traveling in a straight trajectory. Would the tires cause more stress or strain on the ground if moving slower?

You are welcome, Sir.
The tires would not cause more stress or strain on the ground if moving slower.

 

[jbriggs444]

You are welcome, Sir.
The tires would not cause more stress or strain on the ground if moving slower.

Why not more stress? Why not more strain?

 

[Lnewqban]

Why not more stress? Why not more strain?

I may be wrong, but I assume that neither static or dynamic loads on the interphase (contact patches-asphalt) could be greater for the same vehicle, road's surface and dynamic conditions.

 

[jbriggs444]

I may be wrong, but I assume that neither static or dynamic loads on the interphase (contact patches-asphalt) could be greater for the same vehicle, road's surface and dynamic conditions.

"Strain" is not about load. It is about deflection.