Kinetic to Static Friction

In summary, the conversation discusses the transition from kinetic friction to static friction in truck or tractor pulls. The weight on the front plate of the drag increases at a constant rate, causing a drop in speed and eventually bringing the entire system to a halt. The sled's velocity profile plays a role in this transition, with an initial acceleration, a plateau of constant velocity, and a deceleration to a complete stop. Once the kinetic friction matches the drawbar of the tractor, the sled comes to a halt and requires a larger force to overcome static friction.
  • #1
steel_cow
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Are there any fans of truck or tractor pulls out there? I am trying to understand what is happening to the coefficient of friction as the sled transitions from kinetic friction back to static friction.

It is a fairly complicated model...

The weight imposed on the front plate of the drag is increasing at a constant rate as the sled and tractor move down the track. As the load on the sled increases, and is transferred to the tractor, there is a resultant drop in speed. Eventually, the entire system comes to a hault.

What does the transition from Kinetic friction back to Static friction look like?
 
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  • #2
The weight imposed on the front plate of the drag is increasing at a constant rate as the sled and tractor move down the track.

The track that moves the weight forward from the rear of the sled to the front is on a track geared directly to the rear wheels of the sled. The weight will move forward in direct proportion to the forward speed of the sled. If the sled forward movement did not slow down as the pull prgresses, then yes that would be a constant rate forward or constant velocity forward of the weight. If the weight had a mass M, then if the sled was being pulled at constant velocity, then theoretically you could plot on a graph the normal force of the sled on the ground as a function of time or distance traveled as a straight line plot from 0 to Mg or even greater than Mg if there is some kind of overhang.

The sled does speed up and does slow down though so there is nothing about a constant rate.

You would have to know the velocity profile of the sled as the tractor is pulling it. Perhaps studying some of the videos you could get a grasp how it does paly out. I would expect there is an initial acceleration, a plateau of something similar to a constant velocity and a deceleration to a complete stop, with a lot of black exhaust smoke and dust.

Assuming the coefficient of kinetic fricion is constant, the sled would keep moving forward until the kinetic friction matches the drawbar of the tractor and the tractor wheels start spinning on the Earth and the the thing quickly comes to a halt. At that point the sled being stopped would require a larger force to move irt to overcome static friction.

Hopefully that gets you started.
 

1. What is kinetic friction?

Kinetic friction is the force that resists the motion of an object as it slides or moves across a surface. It is caused by the microscopic bumps and imperfections on the two surfaces that come into contact.

2. How is kinetic friction different from static friction?

Kinetic friction occurs when an object is already in motion, while static friction occurs when an object is at rest and trying to be put into motion. Static friction is typically greater than kinetic friction.

3. What factors affect the magnitude of kinetic friction?

The magnitude of kinetic friction is affected by the types of surfaces in contact, the force pressing the surfaces together, and the relative speed at which the surfaces are moving.

4. How is the coefficient of kinetic friction calculated?

The coefficient of kinetic friction is calculated by dividing the force of kinetic friction by the force pressing the surfaces together. It is a dimensionless quantity typically denoted by the symbol "μ".

5. What are some real-life examples of kinetic friction?

Kinetic friction can be observed when a car is braking, when a person is walking, or when a box is being pushed across the floor. It is also responsible for the heat generated when rubbing your hands together.

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