Problem understanding rolling motion

• Phyman1109
In summary, when you roll a pen under your hand, the pen moves the same distance as the length of your hand, which is half the length of the pen.
Phyman1109
we know that in rolling motion the top of drum has linear velocity 2v if the centre of mass has linear velocity v. thus if a board moves over a drum without slipping it wil roll 2vt=2L if the center of mass moves vt=L in time t, and this result is independent of size of the drum. but when i do this with a pen or pencil rolling by my hand i always find that the pen moves the distance equal to length of my hand. do it yourself and please comment on this.

Phyman1109 said:
we know that in rolling motion the top of drum has linear velocity 2v if the centre of mass has linear velocity v. thus if a board moves over a drum without slipping it wil roll 2vt=2L if the center of mass moves vt=L in time t, and this result is independent of size of the drum. but when i do this with a pen or pencil rolling by my hand i always find that the pen moves the distance equal to length of my hand. do it yourself and please comment on this.
So you are claiming that when you roll your hand over a pen, that the pen moves at the same rate as your hand? So if you start with the pen at your fingertips, the pen remains at your fingertips as your hand moves? I don't see how that is possible.

Better try that again!

Doc Al said:
So you are claiming that when you roll your hand over a pen, that the pen moves at the same rate as your hand? So if you start with the pen at your fingertips, the pen remains at your fingertips as your hand moves? I don't see how that is possible.

Better try that again!
i am saying that when i roll the pen under my hand from fingertips to end of palm without letting my hand slip over the pen, the pen traverse the same distance as the length of my palm which it should cover only half of the length.

Phyman1109 said:
i am saying that when i roll the pen under my hand from fingertips to end of palm without letting my hand slip over the pen, the pen traverse the same distance as the length of my palm which it should cover only half of the length.
Compare the distance your hand moves with respect to the table with the distance the pen moves. Your hand moves twice as far.

Thus your hand moves with respect to the pen (which is moving) the same distance that the pen moves with respect to the table. This is what you are describing, which makes perfect sense.

Doc Al said:
Compare the distance your hand moves with respect to the table with the distance the pen moves. Your hand moves twice as far.
oops..i got it..i was making a mistake: i was measuring distance to end of the palm. Thanks.

What is rolling motion?

Rolling motion is a type of motion in which an object moves forward while also rotating around a fixed axis. This is commonly observed in objects like wheels, balls, and cylinders.

What causes rolling motion?

Rolling motion is caused by the friction between the object and the surface it is rolling on. This friction creates a torque that causes the object to rotate as it moves forward.

How is rolling motion different from sliding motion?

In rolling motion, the object is in continuous contact with the surface it is rolling on, while in sliding motion, there is no such contact. Additionally, rolling motion involves both translational and rotational motion, while sliding motion only involves translational motion.

What are some real-life examples of rolling motion?

Some common examples of rolling motion include a car moving on its wheels, a ball rolling down a hill, and a bicycle moving forward while its wheels rotate.

How is rolling motion relevant in scientific research?

Rolling motion is relevant in many scientific fields, such as physics, engineering, and robotics. Understanding the principles of rolling motion can help in designing and optimizing various machines and mechanisms, as well as in studying the movement of objects in different environments.

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