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# Tag Archives: moment of inertia

## Theorem of parallel axis

State the theorem of parallel axes for the **moment of inertia**.

Maulik

## Physics of Diving

When a high diver in a swimming event springs from the board and “tucks in”, a rapid spin **result**. Why is this?

Answer: This is the consequence of **conservation** of **angular** momentum.

The **angular** momentum of a **body** is the **product** of Moment of inertia (*A measure of rotational inertia and it depends on the mass as well as distribution of mass about the axis of rotation. Farther the masses, greater will be the rotational inertia*) and the

**angular**

**velocity**(The speed of

**rotation**)

The **angular** momentum of a **body** remains unchanged in the **absence** of any external torque.

When the diver dives, he is giving his **body** a turning and takes off with his limbs stretched. In the stretched **position**, the **moment of inertia** is more. When he “tucks in”, the **moment of inertia** decreases. But since this happens without any external torque, it would **result** in an increase in **angular** **velocity** so as to keep the **angular** momentum constant.

## How wheel + Tyre diameter affects a vehicle’s speed

I have been told a larger wheel/tyre decrease acceleration because its harder to turn the wheel making the car rev slower.

But the same person tells me it will increase the top speed.

My question is if the car has a max rev of 8000rpm but only reaches 7000rpm in its highest gear would a smaller wheel/tyre not make it easier for the car to rev higher thus possible increasing the top speed by using a smaller wheel?

(Garry asked)

**Answer**:

**top speed**other conditions remaining the same.

## What is the Physics involved when a cat dropped upside down lands on four legs?

If a cat is held upside down and dropped, it is able to execute a twist and to land upright, even if it has no initial angular momentum.

*To Quote from Conceptual Physics by Paul G Hewitt:*

“Zero-angular momentum twists and turns are performed by turning one part of the body against the other. While falling, the cat rearranges its limbs and tail several times to change its rotational inertia (moment of inertia) repeatedly until it lands feet downward. During this maneuver the total angular momentum remains zero. When it is over, the cat is not turning. This maneuver rotates the body through an angle, but it does not create continuing rotation. To do so would violate angular momentum conservation”