# Using Newton's Laws: Friction, Circular Motion, Drag Forces

• Sunwoo Bae
In summary, the conversation discusses setting up an equation to find the acceleration of a box and using it to solve for the value of (x-x0). The solution sheet suggests that in the second stage, F should be 0 and the only force acting on the box should be Ffr. However, there is confusion about how F can be 0 when the box was given an initial push. The conversation also mentions that the motion occurred in two stages, with the first stage being unknown and the second stage where F=0 and the box decelerates under friction.
Sunwoo Bae
Homework Statement
A box is given a push so that it slides across the floor. How far will it go, given that the coefficient of kinetic friction is 0.15 and the push imparts an initial speed of 3.5m/s?
Relevant Equations
F-Ffr= m*a
v^2=(v0)^2+2*a(x-x0)
Here is my attempt at setting up the equation:
I set up the equation to find the acceleration of the box:
F-Ffr= m*a
after finding the acceleration, I can use the acceleration and plug it in the formula v^2=(v0)^2+2*a(x-x0), which will get me the value of (x-x0)The solution sheet says that F should be 0, and Ffr should be the only force acting on the box. However, I do not understand how F can be 0 when the box is given a push, and the push initiates the initial velocity of 3.5m/s. How can F be 0?

Sunwoo Bae said:
I do not understand how F can be 0 when the box is given a push,
The motion occurred in two stages. First, the box was accelerated from rest by an unknown force and at an unknown acceleration. Second, the unknown force was terminated and the box allowed to decelerate under friction to a stop.
You are not asked anything about the first stage. You only have to consider the second stage, and in that stage F=0.

## 1. What is friction and how does it affect motion?

Friction is a force that opposes the relative motion between two surfaces in contact. It is caused by the microscopic irregularities of the surfaces and it acts in the direction opposite to the applied force. Friction can either slow down or prevent motion altogether.

## 2. How do Newton's laws relate to circular motion?

Newton's laws of motion can be applied to circular motion by considering the forces acting on an object moving in a circle. The first law states that an object will continue moving in a straight line at a constant speed unless acted upon by an external force. In circular motion, this external force is the centripetal force, which is directed towards the center of the circle.

## 3. What is the significance of drag forces in motion?

Drag forces, also known as air resistance or fluid resistance, are forces that act in the opposite direction of an object's motion. They are caused by the interaction between the object and the fluid (such as air or water) it is moving through. In many cases, drag forces can significantly affect the speed and direction of an object's motion.

## 4. How can friction and drag forces be reduced?

Friction can be reduced by using a lubricant or by making the surfaces smoother. Drag forces can be reduced by streamlining the shape of an object, reducing its surface area, or by decreasing the density of the fluid it is moving through.

## 5. Are there any real-world applications of these laws?

Newton's laws of motion, including the concepts of friction, circular motion, and drag forces, have many real-world applications. For example, they are used in engineering design to calculate the forces acting on structures and vehicles, in sports to improve performance and safety, and in physics experiments to study the behavior of objects in motion.

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