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Laws of friction


Here we are going to learn about Laws-of-Friction.

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    A box needs to be moved across the floor of your room, so you give it a strong push and then let go. The object will continue moving to the other side of the room because you learned in physics class that when an object is in motion it will move at a constant speed until it’s acted on by another force (in other words, Newton’s First Law of Motion).

    However, that isn’t what happened! The box slowed and stopped as soon as you let go. Is this an indication that Newton’s First Law does not apply? This indicates that there is another force acting upon the box on the box.

    Friction causes the motion to slow down and eventually stop. The friction that occurs when two solid surfaces slide past each other is called sliding friction, though there are other types as well, such as fluid friction and rolling friction.

    Discover how objects react to one of the forces of motion when they are exposed to the laws of friction. Study friction types, frictional forces, and normal forces as well as the details of each of the five laws. There are a few types of friction, which are similarly categorized into three properties called laws. The reason friction is crucial is that it allows us to keep a specific position and to develop in that position by enabling us to hold things or surfaces in place. The current materials and beings on this planet are incapable of supporting any sort of development without friction and will continually slip and fall mainly because friction is the reason for contact.

    Different types of friction

    Static friction and dynamic friction are two types of friction.

    An internal friction

    In a solid material, it is that force that prevents motion between its constituent parts when the material is deformed.

    The external friction

    When two bodies are in contact, if they have the tendency to move, or if they are actually moving relative to each other, this occurs. Friction can exist in many forms, including Dry friction, Fluid friction, Lubricated friction, and Skin friction. Friction resulting from the movement of viscous fluids between layers is called fluid friction.

    Any lubricant fluid present between two solid objects results in lubricated friction. Friction occurs when a force prevents fluid from moving across the surface of any body.

    The friction of dry surfaces

    Two solid surfaces in contact may be restricted in their relative lateral movement by a force called dry friction or external friction; it may be further divided into static friction, limiting friction, and kinetic friction.

    Static Friction

    The tendency of relative motion occurs on non-moving solid surfaces when the bodies in contact are at rest and in contact with one another. It is represented by the function f s. Friction cannot exist without static contact. The applied force opposes the impending motion, so the motion always occurs under that force. If no applied force is present, static friction does not exist. Static friction has a variable value and is self-adjusting.

    The value is unknown, so there is no formula to calculate it. Limiting friction refers to the maximum value of static friction, also referred to as f limiting. Here are some examples of the value of static force:

    0 ≤ f s ≤ f limiting

    F limiting = μs N

    Where mu s is the static friction coefficient, and N is the normal reaction exerted by the surface.

    Laws of Static Friction:

    The magnitude of the maximum. There is no relation between the static friction force and the area of contact between two surfaces.

    Maximum forces are always relative to normal forces, so if normal forces increase, the maximum external force the object can withstand without moving will also increase.

    Limiting Friction

    It is the maximum force of static friction that occurs when two bodies are in contact and just start moving over one another’s surface. We can calculate it using the following equation:

    F limiting = μs N

    μs is the coefficient of static friction or limiting friction, and N is the normal reaction of the surface.

    Laws of Limiting friction:

    Friction is limited by the following four laws:

    1. There is a direct relationship between friction force and normal reaction force: F ∝ N
    2. A heavy body, therefore, has a normal reaction, or mg, which means force increases; therefore, more force is required to move a heavy body compared with a lighter one. Whenever one object is about to move over another, the direction of friction is opposite to the direction in which it is moving.
    3. Friction limits the force between two bodies regardless of the distance between the bodies.
    4. It depends on the materials or the roughness and smoothness of the objects in contact on how much friction they generate.

    Kinetic Friction

    The phenomenon occurs between moving surfaces or when motion is present. The actual motion begins when the applied force increases slightly more than the limiting friction. Known as ‘Kinetic friction’ at this point, the force of friction here is constant. Its value is constant and does not change based on relative motion or contact area. The symbol F k represents it. The kinetic friction f k is directly proportional to the normal reaction N.

    F k ∝ N

    F k = μ k N

    Where μk = constant and known as the coefficient of kinetic friction, depends on the surfaces which are in contact.

    When we plot a graph between friction and applied force, we find that at rest the static function equals the applied force according to static friction being self-adjusting. This graph, therefore, remains linear and in a straight line. The value of friction always decreases and then becomes constant after the body has reached the stage of limiting friction.

    Laws of Kinetic Friction:

    Kinetic friction is defined by the following four laws:

    A constant amount of kinetic friction opposes the relative motion at all times. Values of contact coefficients vary with the nature of the two surfaces in contact.

    Kinetic friction f k does not depend on the area of contact, so the reaction is the same wherever it is applied. The velocity does not totally determine the kinetic friction. As kinetic friction increases, the normal reaction between the two surfaces in contact increases.

    File:Forces 2 carts connected by string.jpg

    Also read: Static and Kinetic Friction

    Frequently Asked Questions FAQs:

    Que: What types of friction are there?

    Ans: A force called friction acts to slow down the moving object as well as to stop the rolling object. Friction can take four different forms. There are different types of friction for different types of motion. Four categories can be distinguished.

    Static friction: Objects resting on a surface experience static friction, which is friction that exists between the object and the surface. Static friction prevents an object from slamming into the surface.

    Sliding friction: When two items slide against each other, sliding friction occurs. A second force must be present to keep the body moving when sliding friction is present.

    Rolling Friction: The resistance that slows the speed of a rolling ball or wheel is known as rolling friction. The term is also used as a synonym for rolling resistance. When a force or torque is applied to a stationary wheel, a modest static friction force holds it back from rolling. As opposed to static sliding friction, static sliding friction is what actually makes the wheels roll the rolling friction on a surface slows down an object’s speed by preventing it from rolling.

    The friction caused by flowing fluid affects objects traveling through the open air. The friction occurs when the object is in contact with the air it is traveling through. Similarly, drag occurs when an object is in contact with the air. Object shape, substance, movement speed, and viscosity determine the force applied. As a function of density, viscosity is a measure of air resistance.

    Que: When a sled weighing 1200.0 kg f is slid over a flat surface, a force of 980.0 N is required. How Do You Calculate the Friction Coefficient?

    Ans: If f s = 980 N, then

    Normal-force = 1200 ×9.8 N

    Static friction is measured by the coefficient of friction (CST)

    µs = f s / N

    = 980.0 / 1200.0 × 9.8

    = 0.83

    Que: A boy pushes a cardboard box along a flat surface of a floor with a 75.0 kg weight. The coefficient of Kinetic Friction k is 0.520. Determine the force exerted by the boy if he exerts 400.0 N. What is the magnitude of friction?

    Ans: Using the equation below, we can determine the normal force on any object.

    N = mg

    When we substitute 75.0 x 9.8 in the equation F k = *k N, we get (using 9.8 m/s2 as g)

    F k = (0.520) (75.0) (9.80) = 382.20 N

    The following formula must be used to calculate the net force that moves the box:

    As the net force acting on a body is always the sum of all forces acting on an object, Fnet = Fworker – Fk. A person’s force plus kinetic friction in the opposite direction act on the given body here. Due to the forward movement being positive, the net force will be as follows:

    Net F worker = F worker – F k

    As a result of substituting the values in the equation above, we get

    F net = 17.8 N

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