Vehicle dynamics -- Accelerating FBD

In summary, the conversation discusses the topic of vehicle dynamics and the use of free body diagrams (FBD) to analyze the movement of the center of mass of a vehicle. There is a question raised about the consistency of the tangent forces to the wheel when the vehicle is accelerating uphill. The speaker mentions the diagrams provided by Gillepsie and questions the correctness of the friction forces shown in the FBD. It is clarified that the friction forces are correct and the direction of the forces depends on whether the ground or the car is being isolated. The concept of rolling resistance is also mentioned and it is noted that it always produces a reacting torque to slow down the rotation of the wheels.
  • #1
Eduardo1234
1
0
Im starting to learn about vehicle dynamics by watching video lectures here , and also reading the books by Gillepsie and Jazar. I´ve got a fundamental question about the FBD of the vehicle.

According to Gillepsie :http://imgur.com/a/lGXxw
http://imgur.com/a/lGXxw

The vehicle is accelerating uphill.
But aren't the tangent forces to the wheel inconsistent to the way the wheels should turn when going in that direction.Or this way of FBD is simplifying the rolling analysis in some way just to analyse the movement of the center of mass in de x direction.
 
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  • #2
What do you mean by "tangent forces to the wheel"? The diagram names all the forces, can you tell us the name of the force you think is wrong? Are you referring to the friction ("tractive") forces Fxf and Fxr ? They appear to be correct (up the slope).
 
  • #3
If you isolate the ground and do a FBD, the friction force will be in the opposite direction, i.e. the car pushes on the ground. But when you isolate the car, on the FBD, the friction force seen by the car is the ground pushing on the car.

For the rolling resistance, by definition, it must always produce a reacting torque (not shown in next figure) slowing down the rotation, otherwise it wouldn't make sense.

rolling-resistance.gif
 

1. What is vehicle dynamics?

Vehicle dynamics is the study of how a vehicle moves and responds to different forces and inputs, such as acceleration, braking, and steering. It involves understanding the mechanical and physical aspects of a vehicle and how they interact to affect its performance.

2. What is an FBD in the context of vehicle dynamics?

FBD stands for Free Body Diagram, which is a graphical representation of all the forces acting on a vehicle at a particular moment in time. It is a useful tool in analyzing the dynamics of a vehicle and understanding the forces that are influencing its motion.

3. How does acceleration affect a vehicle's FBD?

Acceleration is a force that causes a change in the velocity of a vehicle. In terms of FBD, it is represented as a force arrow pointing in the direction of the acceleration. The magnitude of the arrow is determined by the mass of the vehicle and the rate of acceleration.

4. What are the main factors that affect a vehicle's acceleration?

The main factors that affect a vehicle's acceleration are its engine power, weight, and the friction between its tires and the road surface. A more powerful engine, lighter weight, and better tire grip can all contribute to a higher acceleration rate.

5. How can understanding vehicle dynamics and FBDs be useful in designing a car?

Understanding vehicle dynamics and FBDs is crucial in designing a car that performs well and is safe to drive. By analyzing the forces acting on a vehicle, engineers can make design decisions that optimize its performance, handling, and stability. This can result in a more efficient and enjoyable driving experience for the driver.

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