1 Physics -- Rotational Dynamics

Explain in terms of angular momentum and rotational inertia, exactly how one "pumps up" a swing in the sitting position.

1 Answers

When one sits in the sitting position, the rotational inertia of the body decreases. Since no external torque acts on the swing during this, the change of angular momentum must be conserved. To ensure this, the decrease in rotational inertia of the body must be compensated by increase in angular velocity, and the increased angular velocity eventually pumps up the swing.

A flat uniform disk of radius 2R has a hole of radius R removed from the center. The resulting annulus is then cut in half along the diameter. The remaining shape has mass M. What is the moment of ...

What is the purpose of the spin cycle of a washing machine? Explain in terms of acceleration components.

The spin cycle in washing machine spins the clothes in the washing machine making them move circular. the continious circular motion by the spin cycle gives centripetal and pseudecentripetal ( centrifugal ) force. after the completion of wash, the centrifugal force generated makes the water in the clothes get extracted due to high force ( caused by acceleration due to the spin cycle ) and make clothes dry. so, it primarily acts as moisture absorbent.

How might you determine experimentally the moment of inertia of an irregularly shaped body about a given axis?

Using the parallel axis theorem

We note the angular speed and also the system energy. Using these information we calculate the moment of inertia of irregular shaped body.

Io=2E/w²

When we have moment of inertia of irregular shaped body, we can then use parallel axis theorem to solve the moment of inertia if the body about the given axis.

I=Io+md²

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To maximize the moment of Inertia of a flywheel while minimizing its weight, what shape and distribution of mass should it have? Explain.

We know that the moment of inertia of any rotating body is directly proportional to the square of the distance from its rotational axis. In the case of a flywheel, the position of an individual particle from the rotational axis matters for determining its moment of inertia. So, in order to maximize the moment of inertia, while minimizing its weight, we have to make a flywheel with the maximum possible radius while having gaps in the body, i.e. having spoke-like structures to hold the wheel. A...

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I, personally loved this problem. Though I am not that much interested in playing sports on my own, I love the beauty of physics behind each sport, and the way physics beautifies each sport.

Before approaching the question, let's know how diving is scored in Olympic games. The judges score looking at the starting position, approach, height, flight, and entry. The higher jump with a maximum number of somersaults and a perfect entry with a minimal splash is always considered the best one.

In the...

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Get the answer from Yo Yo Master.

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A student stands on a table rotating with an angular speed while holding two equal dumbbells at arm's length. He pulls his hands towards him, what's its consequence? But now, without moving anythin...

The angular speed of the student will increase. When the dumbbells are dropped on the floor, no external torque acts on the student and the turntable, and therefore the angular momentum must be conserved.
When the dumbbells are dropped, the rotational inertia of the student and turntable decreased. To compensate for the decrease in rotational inertia the angular speed of the student and the turntable must increase.

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Why does a long bar help a tightrope walker to keep his or her balance?

You are walking along a narrow rail and you start to lose your balance. If your start falling to the right, which way do you turn your body to regain balance? Explain

A helicopter flies off, its propellers rotating. Why doesn't the body of the helicopter rotate in the opposite direction?

In the air, there's nothing holding the body of the helicopter still - so the rotor blades spin one direction, butthe torque applied to spin the rotors tries to spin the bodyof the helicopter in the opposite direction. The little rotor on the tail helps keep the body of the helicopter pointed in the same direction.

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