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Welcome to our Physics lesson on **The Meaning of Centripetal Acceleration**, this is the fourth lesson of our suite of physics lessons covering the topic of **Kinematics of Rotational Motion**, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

We stated earlier that even when the rotational motion is uniform, the object has not the same velocity because of the change in direction, despite velocity may have the same magnitude. Therefore, we can assign an acceleration to this type of motion which is not as the traditional acceleration which takes place when an object sppeds up or slows down, but only because the velocity vector changes direction and thus, the difference between two such vectors in two different instants is not zero. As a result, when this difference (change in velocity) is divided by the time interval Δt it occurs, we obtain a non-zero acceleration, whose vector is directed towards the centre of circle. This is the reason why it is called "**centripetal acceleration**" (in symbols, a*⃗*_{C}) and not because the object itself point towards the centre. Look at the figure.

We can write:

a*⃗*_{C} = *v**⃗*_{2}-v*⃗*_{1}*/**∆t*

Obviously, the magnitude of centripetal acceleration does not depend only on the magnitude of velocity itself, but also on the radius of curvature. This is because greater the radius, larger the circle and smoother the curve. This means arcs resemble more and more to straight lines. When radius of circle is so long that arcs become straight, we cannot speak for centripetal acceleration anymore as it exists only in rotational motion. As an example in this regard, we can mention objects moving at short distances on Earth surface. We consider such paths as linear, despite the fact that the Earth is a sphere.

Therefore, we calculate the magnitude of centripetal acceleration by the formula

a_{C} = *v*^{2}*/**r*

The unit of centripetal acceleration is [m/s^{2}] although it is an acceleration that occurs only in rotational motion. Therefore, centripetal acceleration acts as a bridge between linear and rotational quantities.

Since the object is at rest, the only velocity we can assign to it, is the velocity of Earth rotation around itself. However, it is more convenient to use the concept of speed instead of velocity here, as we can apply the equation

v = *2πR**/**T*

where T = 24 h = 24 × 60 × 60 = 86400 s and R = 6371 km = 6 371 000 m. Therefore, we have

v = *2 × 3.14 × 6371000 m**/**86400 s*

= 463*m**/**s*

= 463

Therefore, centripetal acceleration of the person at equator is

a_{C} = *v*^{2}*/**r* = *463*^{2}*/**6 371 000* = 0.03 *m**/**s*^{2}

Compared to gravitational acceleration (g = 9.81 m/s^{2}) this centripetal acceleration is very small and thus, it is often negligible during the calculations. This is the reason why it is rarely taken into consideration during the soultion of exercises.

You have reached the end of Physics lesson **7.1.4 The Meaning of Centripetal Acceleration**. There are 4 lessons in this physics tutorial covering **Kinematics of Rotational Motion**, you can access all the lessons from this tutorial below.

Enjoy the "The Meaning of Centripetal Acceleration" physics lesson? People who liked the "Kinematics of Rotational Motion lesson found the following resources useful:

- Centripetal Feedback. Helps other - Leave a rating for this centripetal (see below)
- Rotation Physics tutorial: Kinematics of Rotational Motion. Read the Kinematics of Rotational Motion physics tutorial and build your physics knowledge of Rotation
- Rotation Revision Notes: Kinematics of Rotational Motion. Print the notes so you can revise the key points covered in the physics tutorial for Kinematics of Rotational Motion
- Rotation Practice Questions: Kinematics of Rotational Motion. Test and improve your knowledge of Kinematics of Rotational Motion with example questins and answers
- Check your calculations for Rotation questions with our excellent Rotation calculators which contain full equations and calculations clearly displayed line by line. See the Rotation Calculators by iCalculator™ below.
- Continuing learning rotation - read our next physics tutorial: Dynamics of Rotational Motion

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