# Q. In Resnick,Halliday,Krane book,in pseudoforces,it's written that: Imagine yourself riding in a car that is rounding a curve to the left.To a ground observer,the car is experiencing a...

Q. In Resnick,Halliday,Krane book,in pseudoforces,it's written that:

Imagine yourself riding in a car that is rounding a curve to the left.To a ground observer,the car is experiencing a centripetal acceleration and therefore,constitutes a non-inertial reference frame.If the car has smooth vinyl seats,you will find yourself sliding across the seat to the right.To the ground observer,who is in inertial frame,your body is simply trying to obey Newton's first law and move in a straight line,and it is the car that is sliding to the left under you.From your point of view in the non-inertial reference frame of the car,you must ascribe your sliding motion to a pseudoforce that is pulling you to the right.

Respected Sir/Madam,will you please make me understand this in simple language?I am really very confused.

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### 1 Answer

By definition, force is a push or pull. According to the First Newton's Law, an object with mass m, when force F is applied to it, will move with acceleration a, determined by the equation F = ma.

When this situation is observed from intertial reference frame, nothing changes. Since inertial frame moves with the constant velocity, its acceleration is zero, and the acceleration of the objects involved does not change.

Not so when this situation is observed from the non-inertial reference frame. Then, the acceleration will change and new acceleration can be found as

`a_(of) = a_o + a_f` ,

where `a_(of)` is the acceleration of the object in the non-intertial frame

`a_o` is the acceleration of the object

and `a_f` is the acceleration of the frame.

If we mulitipy this equation by mass m, we obtain

`ma_(of) = ma_o + ma_f`

The terms in this equation all have the dimension of the force. The term `ma_o` is still the actual physical force that caused the motion of the object in the first place. But the term `ma_f` , which arouse purely from the fact that frame is moving with non-zero acceleration, does not correspond to any actual force. However, since it has dimension of the force, it is called a pseudo-force.

In your example with a car making a curve, your acceleration relative to the car, `a_(of),`

will equlal `a_o` (your acceleration which is 0) plus `a_f` , the acceleration of the car. There is no actual force pulling of pushing you, but you still have acceleration `a_of` due to the pseudoforce

`F=ma_f` .

Hope this helps!

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