How Do You Calculate Friction Forces for a Car on a Flat Surface?

[H4NS]

Homework Statement

A 1326kg car lies on a flat surface. To make it move very slowly (a~0), one needs a force of 160N parallel to the surface. To stop it, the force must be reduced to 120N.

Homework Equations

Calculate the friction forces of the car

On Tuesday I have an exam regarding this and related topics. I missed some classes due to sickness and now I am a little lost.

Thanks in advance!

 

[azizlwl]

According Newton's 2nd law,

F_net=ma

F_net==F₁+F₂+F₃+ ...F_n

Forces are vectors, so they have magnitude and direction.
If you take vector force pointing to the right is positive(vector as an arrow) , then vectors pointing to the left as negative.
As for the friction, the direction is always opposite of the motion of the object.
The value can be calculated by multiplying the Normal force to the kinetic coefficient μ.

 

[CWatters]

If I have understood correctly, the problem statement is telling you that to overcome the static friction you need to apply 160N. However once it's moving you only need to apply >120N to keep it moving. (eg this is a problem about static and dynamic friction).

However is the question really asking you to calculate the "friction forces" or the "coefficients of friction" ?

If the latter, look at the wikipedia entry for coefficient of friction. Hint: It's a ratio.

Sorry but I might not be able to return to this thread later.

 

[H4NS]

If I have understood correctly, the problem statement is telling you that to overcome the static friction you need to apply 160N. However once it's moving you only need to apply >120N to keep it moving. (eg this is a problem about static and dynamic friction).

However is the question really asking you to calculate the "friction forces" or the "coefficients of friction" ?

If the latter, look at the wikipedia entry for coefficient of friction. Hint: It's a ratio.

Sorry but I might not be able to return to this thread later.

Yes, I meant the coefficient.

And also, the stop the car, you reduce the applied force to 120N

According Newton's 2nd law,

F_net=ma

F_net==F₁+F₂+F₃+ ...F_n

Forces are vectors, so they have magnitude and direction.
If you take vector force pointing to the right is positive(vector as an arrow) , then vectors pointing to the left as negative.
As for the friction, the direction is always opposite of the motion of the object.
The value can be calculated by multiplying the Normal force to the kinetic coefficient μ.

I don't have the kinetic coefficient

 

[Nickie]

I can offer some guidance on how to approach this problem. The first thing to consider is the definition of friction force. Friction is the resistance force that occurs when two surfaces are in contact and moving relative to each other. In this case, the car is on a flat surface and is being moved slowly, so we can assume that the friction force is due to sliding friction, which is proportional to the normal force (the force exerted by the surface on the car) and the coefficient of friction (a property of the two surfaces in contact).

To calculate the friction force in this scenario, we can use the equation Ff = μN, where Ff is the friction force, μ is the coefficient of friction, and N is the normal force. In this case, we are given the force needed to make the car move and stop, so we can use these values to find the coefficient of friction.

To make the car move slowly (a~0), we need a force of 160N parallel to the surface. This force is equal to the friction force, so we can set Ff = 160N. We can also assume that the normal force is equal to the weight of the car, which is given as 1326kg. So, we can rewrite the equation as 160N = μ(1326kg x 9.8m/s^2), which gives us a coefficient of friction of approximately 0.012.

To stop the car, we need a force of 120N. Again, this force is equal to the friction force, so we can set Ff = 120N. Using the same assumptions as before, we can rewrite the equation as 120N = μ(1326kg x 9.8m/s^2). Solving for μ, we get a coefficient of friction of approximately 0.009.

In summary, the friction force of the car is directly related to the coefficient of friction and the normal force. By using the given forces and the equation Ff = μN, we can calculate the coefficient of friction for both scenarios. I hope this helps you understand the concept of friction forces and how to approach this type of problem. Best of luck on your exam!