What is impending Motion?
A state of an object just about to slip from a surface is known as impending motion. Such instances occur when static friction reaches its higher limit and is represented by the following equation.
F = µsN
(Image will be Uploaded soon)
However, before moving on with the details of impending motion, first, you must understand static friction.
What is Static Friction?
Static friction refers to the force which can make a body stay at a resting position. Moreover, the static frictional force is a force that is self-operated, which means that static friction will always be opposite and equal to an applied force.
Also, the frictional force’s direction to the Impending motion of bodies is consistently opposite. If the force exerted (P) escalates, then accordingly F (frictional force) also escalates till F < Fs. Here Fs is restricting static frictional force.
Furthermore, if F = Fs, then the object is in a state of unstable equilibrium and begins to move.
Next, take a look at the three different regions of static to moving transition.
The three areas are – impending motion, no motion and motion.
Impending Motion
The impending motion is defined as the state of a body when it is about to slip from any surface. In a similar situation, the static friction will reach its upper limit and is given by the equation
\[F = F_{max}=\mu _{s}N\]
The direction of the frictional force will always be opposite to the Impending relative motion of the surfaces. If the applied force (P) is increased then the frictional force (F) will also get increased, until F < Fₛ (limiting static frictional force). When F = Fₛ then the body is said to possess an unstable equilibrium and said to be in motion.
No Motion
This is the region till which a body will not slip and stay at rest. Moreover, in this scenario, the entire set-up is in equilibrium. So, the static friction is shown using expressions of equilibrium:
F < Fmax
Motion
In this region, an object begins moving in the direction similar to the direction of applying force. However, over here, frictional force reduces to a lesser value. This low value is termed as kinetic friction. So, it is represented by the expression:
F = Fmax = µkN
Additionally, for a more transparent comprehension, have a look at the solved example below to determine the force needed for impending motion.
Solved Example
1. If the coefficient of static friction is 0.2, determine the force necessary for impending motion up the plane.
(Image will be Uploaded soon)
Solution:
All the forces that are acting on the object are shown in the following diagram
(Image will be Uploaded soon)
The gravitational force acting on the body can be found as follows:
Fg = mg
By substituting the values, we get
Fg = 100 kg × 9.8 m / s² = 980 N
To maintain the equation at equilibrium, the sum of the horizontal forces and the sum of the vertical forces should be zero.
∑Fx = 0 and ∑Fy = 0
By taking the vertical component of forces to calculate the normal force
∑Fy = − Fg + N (1213)− Fs (513) = 0
By substituting the value of the gravitational and the coefficient of static friction,
we get,
∑Fy = −980 + N (1213) − 0.2 N (513) = 0
N (1213) − 0.2 (513) N = 980 N
= 9801311 = 1158 N
The normal force = 1158 N
Now, to find the pushing force let us look at the horizontal forces
−N (513) −Fs (1213) + F = 0
F = N (513) + μN (1213)
F = N (513) + μN (1213)
Substituting the values we get,
F=1158 (513) + (0.2 × 1158) (1213)
= 659 N
The force required for impending motion, F = 659.
Do It Yourself
1. There are three types of friction problems. One of them is:
(a) Impending motion at a single point of contact (b) No-Impending motion at a single point of contact (c) Impending motion at all points of contact (d) Apparent Impending motion
FAQs on Impending Motion
1. What is lubricating friction?
Lubricated friction is defined by a situation where a fluid layer separates two solid surfaces. This fluid is the lubricating medium that reduces the force of friction acting between the two bodies as the fluid-solid interaction is characterized by the particles of fluid sliding in between the rough solid surface. This happens due to the flexible shape of the fluid. Therefore, fluid’s action on the surface of the solid reduces the friction experienced by it concerning the relative motion of other solid bodies. That is the reason for the wide use of lubricants in heavy industries to decrease the frictional force acting between two parts of the machine and make their operation smoother.
2. What is fluid friction?
Fluid friction is applicable for certain fluids which have viscosities moving relative to each other. This friction can be easily observed by interacting with honey and cream. Both honey and cream are very viscous fluids, and if tried to mix together, they cannot be mixed. This is due to the friction of fluid present in between them. Fluid friction can also be responsible for the accumulation of charges in gas pipelines which causes a very destructive fire in the facility housing.
3. What is skin friction?
When a solid object is moving through fluid skin friction occurs. For example, a submarine through the ocean. The surface of the solid experiences a frictional force due to the dragging force on the solid body. The dragging force is due to the viscosity of the liquid, which is the relative inertia of the particles of the fluid. The solid-body requires some external force to overcome this internal inertia, and that force is said to be manifested in the form of the drag force.
4. Give some important points regarding Impending motion?
The impending motion states the situation of an item that is about to slip from any surface.
The impending motion occurs when the static friction reaches its maximum limit.
The letter µK refers to the coefficient of kinetic friction. It is however can be used similarly as the coefficient of friction.
Static friction is the force that remains a body at rest.
To move a body it must first overcome the static friction.
Additionally, a body's highest static friction equals s times its standard force.
