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The impending motion describes the situation of an item that is on the verge of slipping off any surface. The approaching motion happens when the static friction approaches its greatest limit, which may be calculated using the equation., F=μsN. When an item is going to slide from its rest position, friction will always resist the direction of sliding at the contacting surface. Consider how the system would move in the absence of friction to identify this direction, which is also known as the direction of oncoming motion. In this article, we will have a look at the three areas of the static to motion transition including impending motion in order to better grasp what approaching motion means.
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What is Impending Motion?
Impending motion is the moment at which a surface begins to slip, and in this instance, static friction has reached its limit. As a result, the frictional force between two bodies in contact is represented as:
F = Fmax = µsN
Also Read: Equations of Motion
Impending Motion
Static Friction
A force that is responsible for the resting position of the body is known as static friction. It is in the opposite direction to the force that is applied, also known as the applied force. When the applied force (P) rises, the frictional force (F) rises with it until F < FS (limiting static frictional force). When F = FS, the body's balance is unstable, and it will move.
Static and Kinetic Friction
Anybody that is about to overcome the force of static friction is said to be in imminent motion. Impending motion, in other words, is the precise moment when the body is going to move. There are two types of friction: static and kinetic. When a body is at rest, static friction occurs. The friction force cancels out the net force applied to the body. Friction does not have a definite direction since it is not a centered force. It's a vector quantity that can only function in opposition to two bodies' relative motion. The friction force applied by one body operates in the opposite direction of the movement attempted by the other body.
Also Read: Types of Friction & Examples
Stages of Transition from Static to Motion
The force that keeps a body in its resting state is known as static friction. Because static friction is always self-operated, it is always in the opposite direction as the applied force. Frictional force always acts in the opposite direction of the oncoming motion of bodies. As the applied force rises, the frictional force increases as well, up to F < Fs. If F=Fs, the item will become unstable and start moving. Between static and moving states, there are three distinct areas: imminent motion, no motion, and motion.
- No Motion: The region up until the point of slippage or oncoming motion is known as No Motion. As long as the system is in equilibrium, the frictional force in this area is specified by equilibrium equations. F < Fmax is used when the motion is not imminent.
- Impending Motion: This is the time when the body is about to fall. The static friction achieves its maximum value at this point. The frictional force is provided by the equation for a given pair of surfaces in contact.
F = Fmax= μsN
- Motion: In this stage, an item begins to move in the same direction as the force is applied. Frictional force, on the other hand, is reduced to a smaller extent here. Kinetic friction is the name given to this low number. As a result, the following expression is used to represent it:
F = Fmax = μkN
Slipping
Applied forces lead to slippage at particular contacting surfaces in a given system. Remember that impending motion happens at a surface where the friction force f and the normal force N are proportional to one other, as F=μsN.
Also Read: Sliding Friction
Things to Remember
- The impending motion describes the situation of an item that is on the verge of slipping off any surface.
- The impending motion happens when the static friction approaches its greatest limit.
- The letter µK stands for coefficient of kinetic friction. It is, however, used in the same way as the coefficient of friction is.
- Static friction is the force that maintains a body in its resting posture.
- The body must overcome static friction in order to move.
- Furthermore, a body's maximal static friction equals s times its standard force.
Also Read:
Sample Questions
Ques. What do you mean by Impending Motion? (2 marks)
Ans. The impending motion describes the situation of an item that is on the verge of slipping off any surface. The approaching motion happens when the static friction approaches its greatest limit.
Ques. What is kinetic friction, and how does it work? (2 mark)
Ans. When an item is moved, it moves in the direction of the applied force. In motion, the frictional force is reduced only a little, and this is referred to as kinetic motion.
Ques. Give an example of the maximum static friction. (2 marks)
Ans. The top limit of the frictional force that retains an item in a resting posture is known as maximum static friction. When static friction reaches its maximum limit, the item begins to move in the direction of applied force.
Ques. What Does µK Mean? (1 mark)
Ans. The letter µK stands for coefficient of kinetic friction. It is, however, used in the same way as the coefficient of friction is.
Ques. In the diagram, calculate the force required for impending motion. The static friction coefficient is 0.2. (5 marks)
Ans. The following is a representation of the free body diagram:
The gravitational force applied to the body is calculated as follows:
Fg=mg
Substituting the values, we get
Fg=100 kg×9.8 m/s2=980 N
The total of the horizontal forces and the sum of the vertical forces should be zero to preserve equilibrium.
∑Fx=0 and ∑Fy=0
To determine the normal force, consider the vertical component of forces.
\(\Sigma F_y = -F_g + N(\frac{12}{13}) - F_s \frac{5}{13} =0\)
In the preceding equation, we get by substituting the value of gravity and the coefficient of static friction.
\(\Sigma F _y = -980 + (\frac{12}{13}) N - 0.2N \frac{5}{13} = 0\frac{12}{13}N - 0.2\frac{5}{13}N = 980N = \frac{980}{\frac{12}{13} - 0.2 \times \frac{5}{13}} =1158 N\)
The normal force is 1158 N
Let's look at the horizontal forces to get the pushing force.
\(- N \frac{5}{13} - F_s \frac{12}{13} + F = 0F = N\frac{5}{13} + \mu N \frac{12}{13} F = N \frac{5}{13} + \mu N \frac{12}{13}\)
Substituting the values we get,
\(F = 1158 \frac{5}{13} + (0.2 \times 1158) \frac{12}{13} = 659 N\)
As a result, F=659N is the force necessary for impending motion.
Ques. Calculate the force and torque necessary to release the clamp as the plane moves down. (3 marks)
Ans.
tan?\((\Phi_s - \theta)\)=\(\frac{Q}{W}\)
=(17.97kN)tan?9.4o Q=2.975kN
Torque =Qr=2.975×5
=2.975×103×5×10-3
=14.87Nm
Ques. What is impending motion? (1 mark)
Ans. Impending motion has a static frictional force whose magnitude is proportional to the normal reaction.
Ques. Explain how oncoming motion is opposed by static friction. (3 marks)
Ans. The force that can keep a body in its resting state is known as static friction. In addition, the direction of frictional force in relation to the upcoming motion of bodies is always the opposite. If the force applied (P) increases, the frictional force (F) increases as well, until F <Fs.
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