# Define Inertial frame of reference and Non-inertial frame of reference

Let’s Define the Inertial frame of reference and the Non-inertial frame of reference. A frame of reference can be any one of these two types: Inertial frame of reference & Non-inertial frame of reference

## Define the Inertial frame of reference & explain

Inertial frame of reference—is that frame of reference in which Newton’s laws of motion are applicable. An inertial frame of reference is one that is either stationary or moving with a constant velocity.

In an inertial frame of reference, the laws of motion are always valid. No imaginary force needs to be ‘made up’ in order to explain the motion of objects within inertial frames of reference.

Since the laws of motion are true for both a stationary frame of reference and for one that is moving with a constant velocity, there is no physical experiment that can be done within an inertial frame of reference to distinguish whether such a frame is stationary or moving at a constant velocity.

To illustrate this, imagine being on an airplane that is flying smoothly at a steady speed. The flight steward serves tea and coffee as easily as in a restaurant; a person can walk up and down the aisle as they would in a cinema; and dropping ball results in it falling vertically under the influence of gravity and no other force. With ear muffs on and the blinds closed, it is not possible to tell whether the plane is indeed in flight or stationary on the ground.

## Define the Non-inertial frame of reference & explain

The non-inertial frame of reference—are those in which Newton’s laws of motion are not applicable. An accelerated frame of reference is a non-inertial frame of reference. A rotating frame of reference is a non-inertial frame of reference.

For a non-inertial frame of reference, the laws of motion do not hold true. For example, if a tennis ball is placed on the floor of a bus, when the bus accelerates forward, the ball rolls backward. For an observer who is inside this non-inertial frame of reference, no force is observed acting on the ball, yet the ball does not remain stationary. This obviously violates the laws of motion since Newton’s first law of motion states that an object will remain stationary or moving with a constant velocity in the same direction unless being acted upon by an unbalanced (net) force.

Here, a fictitious (fake) force, that is, a false backward force, needs to be introduced in order to maintain the validity of the laws of mechanics. The existence of a fictitious force is one of the most distinctive features of a non-inertial frame of reference and allows it to be distinguished from an inertial frame of reference. Such forces are also known as ‘inertial forces or pseudo force’, the centrifugal force is an example.

Define Inertial frame of reference and Non-inertial frame of reference
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