What happens when you write something on a piece of paper? How is the ball capable of moving smoothly right after rolling it? How is it possible to move a cylindrical object very easily, but it is hard when it comes to a rectangular or a triangular object? The answer to all these questions is sliding friction.
Sliding friction is a kind of friction that acts on objects while they are in sliding motion concerning a floor or a surface. In this educational article, let us have a comprehensive look at it while discussing all the related concepts in detail so that the students of Class 8 Science will be able to grasp them.
Sliding friction – Definition
In Class 8 Science, sliding friction is a frictional force that appears when two bodies come into sliding contact. This friction can also be referred to as kinetic friction and is relatively weaker than static friction. For instance, it makes it simpler to slide the furniture over the floor after starting to move it.
Let us see an illustration of how the sliding friction helps while riding a bike:
So, whenever we start riding a bike, there is a presence of sliding friction between the bike rims and brake pads. Due to this friction, the rolling wheels get slowed down, followed by stopping eventually.
Examples of sliding friction
To give the students of Class 8 a better understanding of this friction, let us see some more examples:
- Opening a window
- Skidding of a car while taking a turn in the corner
- A vehicle being slid on the ice or watery roads
- Rubbing the hands together (it also creates heat)
- The activity of sledging
- A child playing on a slide in a park
- A washing machine being pushed along with the floor
- Sliding the coaster against a table
- Sliding of frame and edge of the door sliding against each other
Factors affecting sliding friction
The admirers of Science should be able to understand what the factors that affect sliding friction are,
Factors affecting sliding friction
(Picture credit: Geekforgeeks website)
1. The size of the object:
Sliding friction is directly proportional to the object’s weight. In the universe, it is common for the importance of the thing to be observed in the normal direction.
2. The surface deformation of objects:
Friction is present in every form, be it solid or liquid or gas. However, the friction in the water or air is very low compared to that of the solid. It is because sliding against a solid structure such as a road involves higher friction.
3. The smoothness or roughness of the object’s surface:
Compared to rough surfaces, smooth surfaces can effortlessly slide over to other surfaces. Furthermore, while looking at the microscopic scale, one can notice that the surface that contains irregularities makes it difficult to slide. Therefore, the roughness of the surface is directly proportional to its friction.
4. The actual speed of both the objects:
Whenever the surface temperature increases, it will make the protrusions get flattened slowly. It results in obtaining a steady state at a higher temperature. Due to this, the slide speed would also be higher. Furthermore, there would be additional changes such as reducing sheer force, decreasing friction coefficient, and obtaining low roughness.
5. The amount of pressure on both the objects:
The force acting on the sliding plane’s perpendicular direction can improve the interactions between both surfaces. It results in raising the friction of the surface. This friction can be directly proportional to the applied perpendicular (normal) force.
The formula of sliding friction
The below derived is the formula for sliding friction that acts on sliding surfaces:
Fs = s Fn
Where,
Fs = Sliding friction force
s = Sliding friction coefficient
Fn = normal force
Derivation of friction coefficient
The Class 8 students need to know how the formula is being derived.
1. Reducing the perpendicular force
While placing the object in an inclined direction, there is a reduction in the force, which acts perpendicularly between the surfaces. This reduction is due to the angle of incline.
Therefore, the necessary force to outperform friction Fr equals the friction coefficient times that of the object’s weight (W) time the cosine of the incline angle (cos ). It can be represented as follows:
Fr = W
There is some mathematical tabulation capable of providing the cosine values for certain angles.
2. Contribution of gravity to sliding motion
When an object is fixed on an inclined plane, it will slide down through the ramp due to the gravity force. This force Fg will be found equal to the object’s weight (W) times the sine angle (sin ) .
It is represented using the following formula:
Fg=Wsin
3. Determining the coefficient by the tangent of an angle
The force of gravity Fg is relatively greater than Fr, and the object is subjected to slide down in the incline if the ramp is put at a steep angle. The following equation denotes the angle at which the object begins to slide:
Wcos =Wsin
Now, let us divide W and cos . It will give the equation for static friction coefficient,
=tan
It will be equated to sin cos .
Motion on an inclined surface
A massive object is contained on a slope when an inclined plane is regarded as a problem set. The plane’s movement is dependent on the direction of the inclined surface. The slope’s presence prevents the object from being pulled by gravity. The object can only move along the inclined surface because it is not permitted through the solid surface.
For example, consider putting a book on the ramp and changing its angle. Now, the book will start to slide due to the inclination of the ramp. We could define the friction coefficient between the ramp and the book with this. If the angle obtained is 30°, its tangent is 0.58, denoted as the static coefficient of friction. Furthermore, even if we add more weight to the book, the sliding angle would still be 30°.
Motion on an inclined surface
(Picture credit: Geekforgeeks website)
Normal force
The normal force acting on the plane is not perpendicular to the gravitational force but instead acts opposite to the sliding floor. The normal forces need not necessarily be always facing upward but always act perpendicular to the object’s surface.
Components of gravity force
Both the forces acting on the body exist in opposite directions. Due to this reason, it is difficult to define the net force which acts on an object on an inclined surface. In simple words, to add the forces that act on the object, one of them should be resolved into perpendicular components.
The force that acts at a horizontal angle is resolved into vertical and horizontal components. While dealing with inclined planes, one has to perform splitting the weight vector into two equal components. The weight vector is denoted as F grav. Gravity force is split into two components. One is directed towards the parallel direction to that of the inclined plane, whereas the other is encouraged perpendicular to the inclined plane.
The given figure is a schematic representation of how the gravity force is resolved into two different components, such as a perpendicular and a parallel one.
Force of gravity components
(Picture credit: Geekforgeeks website)
From the above diagram, to balance the normal force, the perpendicular elements of the gravity force can be seen directed in the opposite direction towards the normal force. However, the other forces did not balance the force of gravity’s parallel component. Moreover, with the presence of unbalanced force, the object is capable of being pulled down in the inclined direction.
Parallel components of the gravity force cause the acceleration towards downward motion. It can also be described as the net force.
Furthermore, students of Science are taught the components of the force of gravity in detail.
Sliding vs rolling friction
The Class 8 students should know the occurrence of sliding friction is among two objects of whimsical shape. On the other hand, rolling friction occurs only when an object is in rotational motion. The value of the rolling friction is generally less than the value of the kinetic friction while sliding. Apart from that, the rolling friction’s coefficient values are comparatively lower than that of sliding friction. It helps in generating greater thermal and sound bi-products.
Conclusion
To conclude, the Class 8 Science students can understand sliding friction in detail while also knowing other related factors such as factors affecting sliding friction, the formula for sliding friction, deriving the coefficient of sliding friction, etc.
Apart from that, the students of Class 8 were also taught motion on an inclined plane, normal force, and components of force of gravity. Ultimately, with the help of a differentiation table provided between sliding friction and rolling friction, it becomes very simple to grab the concept in a top-notch way.
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