Concept not understood -- Car tires pushing the car forward....

[Ineedhelpwithphysics]

Homework Statement

Theres this picture and it explains that when a car is going on the road the tire pushes backs and the road pushes forward. How is that possible isnt the the road pushing back on the tire from friction so that means the tire is pushing forward and the road is pushing back.

Relevant Equations

No equation maybe friction

Here is the picture (THIS ISN"T A HOMEWORK QUESTION JUST WANT TO UNDERSTAND A CONCEPT)

I don't understand isn't the tire pushing forward not backward becuase of the friction, road is pushing back.

 

[Lnewqban]

The contact patch of the tire for each instant is the pivot or fulcrum.
The center of the wheel pushes the axle of the car forward.
The pavement “grip” the tire, using static friction, avoiding any slip.

 

[jbriggs444]

I don't understand isn't the tire pushing forward not backward becuase of the friction, road is pushing back.

If you turn off the engine and shift the car into neutral then the car will indeed slow to a stop. The tires will be pushing slightly forward on the road while this happens. Naturally, the road will also be pushing rearward on the tires.

It seems that this part matches your expectations.

But in a car that is driven down the highway, the engine is not turned off. The engine is providing power and forcing the tires to rotate forward. As the tires rotate forward, they tend to apply a rearward force on the highway. Naturally, the highway will be providing a forward force on the tires. This is rather the point of pushing down on the gas pedal.

The interaction of tire with road is an example of static friction. The tires are rolling rather than sliding. The tread in contact with the highway does not move relative to the highway. Static friction acts to oppose the relative motion that would otherwise exist if static friction were not preventing that motion.

 

[PeroK]

Homework Statement:: Theres this picture and it explains that when a car is going on the road the tire pushes backs and the road pushes forward. How is that possible isn't the the road pushing back on the tire from friction so that means the tire is pushing forward and the road is pushing back.
Relevant Equations:: No equation maybe friction

Here is the picture (THIS ISN"T A HOMEWORK QUESTION JUST WANT TO UNDERSTAND A CONCEPT)
View attachment 293308
I don't understand isn't the tire pushing forward not backward becuase of the friction, road is pushing back.

Consider the following experiment. Get the car off the ground suspended in mid air and get the wheels turning. You can have the wheels powered by the engine or not. Now, take a flat piece of wood and place it horizontally against the bottom of the spinning tires. Which way does the wood get pushed?

That's not a perfect analogy for tires on the road. But, there should be no doubt about the direction of the force of the tires on the wood in that case. And, that if you secure the wooden surface, then the reaction force on the tires will be in the expected direction of motion.

 

[Steve4Physics]

I don't understand isn't the tire pushing forward not backward becuase of the friction, road is pushing back.

It should help if you try answering these questions (imagine you are performing the actions described)...

1)You are standing on a rough flat road. You try to walk forwards by applying a backwards on the road with your foot (that’s how you walk!). What happens? What is the direction of the force you exert on the road? By Newton’s 3rd law, what is the direction of the force the road exerts on your foot?

2) You are standing on perfectly smooth/slippery/flat ice (negligible friction). You try to walk forwards by applying a backwards force to the ice with a foot. What happens?

 

[LastScattered1090]

Friction always opposes the motion that would take place if two surfaces that are in contact were able to slide relative to each other.

Here, the two surfaces are the top surface of the road, and the bottom surface of the tire.

In order for the tire to rotate clockwise (which corresponds to forward motion in your diagram), the bottom surface of the tire would have to slide rearward past the road surface. Friction from the road therefore acts to oppose this rearward sliding motion, applying a forward force that propels the car forward.

 

[jack action]

Replace the road & tire with a rack & pinion system. It may be more obvious what is pushing on what.