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Static friction is the force that comes into play when an object is at rest and a force is trying to move it. It is the friction that must be overcome to start moving the object. This type of friction works to resist the initial motion between two surfaces that are in contact. It always acts in the opposite direction to the applied force.
In our problem, the static friction force is determined using the coefficient of static friction, denoted as \(\mu_s\). The maximum static frictional force is calculated as \(f_{s\text{ max}} = \mu_s \cdot N\), where \(N\) is the normal force, which equals the weight of the block.

• The coefficient of static friction in this exercise is 0.650, so we calculate the maximum static friction as \(29.25 \, \text{N}\).
• The applied force is \(36.0 \, \text{N}\), which is greater than the maximum static friction force. Thus, the block overcomes static friction and starts to move.

Static friction is crucial in determining whether an object will start to move when a force is applied. If the applied force exceeds the maximum static frictional force, the object will begin to move.

Once an object starts moving, static friction is no longer at play. Instead, kinetic friction becomes the resisting force. Kinetic friction acts in the opposite direction of the moving object and tends to be less than static friction. This is why objects can appear easier to move once they're already in motion.
In the given situation, we use the coefficient of kinetic friction, \(\mu_k\), to find the kinetic frictional force, calculated as \(f_k = \mu_k \cdot N\). The coefficient of kinetic friction is given as 0.420.

• Thus, the kinetic friction force is calculated as \(18.9 \, \text{N}\).
• This force is subtracted from the initial applied force to calculate the net force, as kinetic friction continues to resist the motion.

Understanding kinetic friction helps us predict how a moving object will behave and is essential for calculating further motion dynamics, such as acceleration.

Newton's second law of motion provides the foundation for understanding how forces affect the movement of objects. It states that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass. This relationship is expressed as \(F = ma\), where \(F\) is the net force, \(m\) is the mass, and \(a\) is the acceleration.
In our example, we first determined the block's mass by using its weight, as weight is the gravitational force acting on the mass. Using the relation \(W = mg\), we derived the mass as \(4.59 \, \text{kg}\).

• The net force acting on the block, once in motion and considering kinetic friction, was found to be \(17.1 \, \text{N}\).
• Using Newton's second law, we calculated the block’s acceleration to be \(3.72 \, \text{m/s}^2\).

Newton’s second law helps us determine the acceleration resulting from forces acting on an object, enabling us to predict and analyze motion effectively.