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# Understanding Pseudo Force

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What is a pseudo force? Explain with the help of an appropriate example.

Solve the following problem using the concept of pseudo force:

Two rectangular blocks are stacked one over the other on a table. The lower and upper blocks have masses of 25 kg and 5 kg respectively. The coefficient of kinetic friction between the lower block and table is 0.3 and that between the two blocks is 0.6. A pulling force is applied to the lower block by means of a mass less rope attached to it.

a) Draw the free body diagram of the lower block "as seen" from the frame of reference of the table (or ground).

b) Draw the free body diagram of the upper block "as seen" i) from the frame of reference of the table (or ground), ii) from the frame of reference of the lower block.

c) At what acceleration of the lower block does the upper block start slipping relative to the lower block?

d) How much pulling force must be applied to the lower block to give it the acceleration calculated at c) above?

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https://brainmass.com/physics/energy/understanding-pseudo-force-556364

## SOLUTION This solution is FREE courtesy of BrainMass!

Force is defined as an effort in the form of a push or pull applied on a body in order to change its state of rest or of uniform motion in a straight line. However, in an accelerated frame of reference this definition of force tends to break down. For example, when a vehicle accelerates suddenly, a passenger sitting in the vehicle is thrown back with a force. Nobody has pulled or pushed the passenger. In other words, no external force as defined above has been applied on the passenger; what then throws her back? The phenomenon is on account of a property of matter known as "inertia". Due to inertia the passenger has a tendency to continue to remain at rest as the vehicle suddenly accelerates forward from rest. The lower part of her body being in direct contact with the seat moves forward along with the vehicle (dragged forward by the frictional force) whereas the upper part tends to remain at rest due to inertia; hence the throwing back.

To understand this phenomenon still better, let us consider a conveyor belt with a crate resting on it (fig.1 in the attachment). For simplicity let us assume there is zero friction between the belt and the crate. The belt initially at rest starts to accelerate at a rate = a as shown in the fig.. An observer A is standing on the belt (with her feet glued firmly to it) and another observer B is standing on the ground. How do the two observers see the crate? As there is no friction between the belt and the crate, there is no forward dragging force on the crate; the belt just slips below the crate. To the observer B (on the ground), the crate appears to be at rest (hence, observer B "sees" no force acting on it). However, observer A, who accelerates forward with the belt, sees the block accelerating backwards with acceleration = a (same as that of the belt in the forward direction). She "sees" a force of magnitude = ma acting on it in the backward direction (as per Newton's second law an object of mass = m accelerating with an acceleration = a must be subjected to a force of magnitude ma in the direction of the acceleration). We know the crate is not subjected to any force as defined earlier (push or pull); nonetheless, observer A "sees" the crate being subjected to a force = ma backwards. This apparent force (a force which appears to act on an object by virtue of the acceleration of the reference frame from which it is viewed) is called "pseudo force". In an accelerated reference frame, pseudo force is to be considered in addition to any other actual force(s) acting on the object.

For solution to the problem please refer to the attachment.

This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!

Â© BrainMass Inc. brainmass.com December 24, 2021, 11:18 pm ad1c9bdddf>
https://brainmass.com/physics/energy/understanding-pseudo-force-556364