Drawing a Wheel Under Acceleration - RWD Car

In summary, the picture shows a wheel under acceleration, with the forces acting on it shown in a free body diagram. The only thing missing is the force V(Fa) acting on the wheel.
  • #1
PhysicsN_b
6
0
I drew up a quick picture in paint of a wheel under acceleration. This is the driving wheel of a RWD car. Am I missing any forces/drawn in the wrong direction?

FBDWheel.png


Thanks.
 
Physics news on Phys.org
  • #2
Assuming all the forces are supposed to be external forces applied to the wheel, then friction force from the road to the tire would be to the right, and the reaction force of the car to acceleration, F = m a, would be to the left and same magnitude as friction force. You also have a clockwise torque force on the wheel from the rear axle (negative sign if using conventional angular math), almost all opposed by the counter clockwise torque related road force and car reaction force. The net torque on the wheel would correspond to the rate of angular acceleration of the wheel divided by it's angular inertia. If you assume that angular inertia of the wheel is zero, then net torque is zero.
 
Last edited:
  • #3
Updated.

FBDWheel-2.png


Assume Rv to be the reaction force of the car on the wheel, and I labeled the angular acceleration z since I cannot due Greek letters in paint. This is correct now right?
 
  • #4
There is no force V(Fa) acting on the wheel. Fg and Fn should have equal magnitude. Ff and Rv should have equal magnitude. Apparently you're not concerned about torques on the wheel.
 
  • #5
I don't understand how I am not concerned with the torque applied on the wheel. If there is angular acceleration on the wheel, there has to be a torque applied. Also, the wheel has to be applying a forward force V(Fa) for the car to accelerate in speed correct, so at the axle there would be a forward force applied? I don't understand what I am missing.
 
  • #6
PhysicsN_b said:
I don't understand how I am not concerned with the torque applied on the wheel. If there is angular acceleration on the wheel, there has to be a torque applied.
If your model uses a non-zero value for angular inertia of the wheel then there's a small net torque on the wheel, most of the torque ends up accelerating the car. If your model uses a zero value for angular inertia of the wheel, then there is no torque due to angular acceleration of a massless wheel, and all of the torque ends up accelerating the car.

PhysicsN_b said:
Also, the wheel has to be applying a forward force V(Fa) for the car to accelerate in speed correct, so at the axle there would be a forward force applied?
A free body diagram is supposed to show only the forces acting on the wheel, and not the forces generated by the wheel.
 
  • #7
Okay. So the only thing I need to get rid of is V(Fa) and 'say' that z is non zero and it should be perfect to be an example of a driving/accelerating wheel?
 
  • #8
PhysicsN_b said:
Okay. So the only thing I need to get rid of is V(Fa) and 'say' that z is non zero and it should be perfect to be an example of a driving/accelerating wheel?
Close enough. In the real world, there would be rolling resistance, aerodynamic drag, energy losses in the drive train, but for a typical physics problem, it's good enough.
 

Related to Drawing a Wheel Under Acceleration - RWD Car

1. How does a RWD car's acceleration affect the drawing of a wheel?

When a RWD (rear-wheel drive) car accelerates, the engine's power is transmitted to the rear wheels, causing the car to move forward. This movement creates a force called inertia that acts on the car's center of mass, which is typically located closer to the rear wheels. This force causes the rear wheels to push against the ground, resulting in a rotation of the wheels. As a result, the drawing of the wheel will appear elongated in the direction of acceleration.

2. Why is the wheel drawn elongated instead of a perfect circle?

The elongation of the wheel drawing is due to the principle of inertia. According to Newton's first law of motion, an object in motion will remain in motion unless acted upon by an external force. In this case, the force of acceleration causes the rear wheels to rotate and creates a perception of elongation in the wheel's shape.

3. Is the acceleration of the car the only factor that affects the drawing of the wheel?

No, there are other factors that can affect the drawing of the wheel under acceleration. These include the car's speed, the weight distribution of the car, and the condition of the road surface. The faster the car accelerates, the greater the force of inertia, resulting in a more elongated wheel drawing. The weight distribution of the car can also impact the amount of force applied to the rear wheels, affecting the shape of the wheel drawing. Additionally, the condition of the road surface can affect the traction of the rear wheels and the resulting rotation of the wheels.

4. What happens to the wheel drawing when the car decelerates?

When a RWD car decelerates, the force of inertia acts in the opposite direction, causing the rear wheels to rotate in the opposite direction. This results in the wheel drawing appearing compressed in the direction of deceleration.

5. Are there any differences in the drawing of the wheel for a FWD (front-wheel drive) car?

Yes, there are differences in the drawing of the wheel for a FWD car. In a FWD car, the engine's power is transmitted to the front wheels, causing the front wheels to push against the ground during acceleration. As a result, the wheel drawing will appear elongated in the direction of acceleration, similar to a RWD car. However, during deceleration, the wheel drawing will appear compressed in the direction of deceleration, opposite to a RWD car.

Similar threads

Replies
15
Views
2K
  • Mechanics
Replies
10
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
920
  • Classical Physics
Replies
3
Views
1K
Replies
6
Views
969
  • Engineering and Comp Sci Homework Help
3
Replies
102
Views
4K
Replies
7
Views
2K
Replies
21
Views
2K
  • Classical Physics
Replies
8
Views
827
  • Classical Physics
3
Replies
95
Views
5K
Back
Top