# Rotational Motion: Meaning of ∫v(t)dt - ∫Rw(t)dt

• gsimo1234
In summary, rotational motion is the movement of an object around a fixed point or axis, commonly seen in objects like wheels, gears, and planets. ∫v(t)dt represents the integral of velocity with respect to time and is used to calculate displacement, while ∫Rw(t)dt represents the integral of rotational velocity and is used to calculate angular displacement. These two integrals are related by the radius of rotation, which is important in understanding rotational motion in fields such as engineering, physics, and biology.
gsimo1234
This is merely a simple, but conceptual, problem. Say we have a cue ball of mass M and Radius R rolling without slipping on the pool table. What is the the meaning of the ∫v(t)dt - ∫Rw(t)dt where w(t) is the angular speed of the pool ball.

My guess is that this represents the length the ball has moved and the amount of radians that the ball has spun through. Am I correct?

You are correct about the first integral but not the second. Do dimensional analysis and you will see why.

Your guess is partially correct. The integral of v(t)dt represents the displacement of the ball, or the distance it has moved along its path. This is because v(t) is the velocity of the ball at any given time, and integrating it over time gives us the change in position.

The integral of Rw(t)dt, on the other hand, represents the angular displacement of the ball. This is because w(t) is the angular speed of the ball, and integrating it over time gives us the change in the angle through which the ball has rotated.

Therefore, the difference between these two integrals, ∫v(t)dt - ∫Rw(t)dt, represents the net displacement of the ball, taking into account both its linear and angular motion. In other words, it represents the total distance and direction that the ball has moved on the pool table.

It's also worth noting that since the ball is rolling without slipping, the relationship between its linear and angular speed is given by v = Rw, where v is the linear speed, R is the radius, and w is the angular speed. This means that we can rewrite the integral of Rw(t)dt as ∫v(t)/R dt, which further emphasizes the connection between the two integrals.

In summary, the integral of v(t)dt - ∫Rw(t)dt represents the net displacement of a rolling ball on a pool table, taking into account both its linear and angular motion. It is a useful concept in understanding the overall motion of rotating objects.

## 1. What is rotational motion?

Rotational motion refers to the movement of an object around a fixed point or axis. This type of motion is commonly seen in objects like wheels, gears, and planets.

## 2. What is the meaning of ∫v(t)dt?

∫v(t)dt is known as the integral of velocity with respect to time. It represents the area under the velocity-time curve and is used to calculate the displacement of an object over a given time interval.

## 3. What does ∫Rw(t)dt represent?

∫Rw(t)dt is the integral of rotational velocity with respect to time. It is used to calculate the angular displacement of an object over a given time interval.

## 4. How are ∫v(t)dt and ∫Rw(t)dt related?

∫v(t)dt and ∫Rw(t)dt are related by the radius of rotation, R. This means that for the same time interval, the angular displacement will be larger for a larger radius of rotation, and vice versa.

## 5. Why is understanding rotational motion important?

Understanding rotational motion is important in many fields, including engineering, physics, and biology. It allows us to design and analyze complex systems such as engines, turbines, and rotor blades. It also helps us understand the movement of living organisms, such as how animals walk or fly.

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