Angular Acceleration and Gravity

[AManNamedPhil]

Hello all,

The other day I observed an occurrence in my Physics class which I do not understand. The teacher set up a rotating platform with a second platform attached to it, so it made a 45 degree angle with the rotating platform.

He then proceeded to put a ball at the top of the second platform, and spun the whole thing and the balls did not fall for quite some time ~30 seconds.

How come the ball doesn't immediately roll down the elevated platform? I have thought about this and don't really get it.

Thanks

 

[Ian]

Phil,
The ball on the second platform will experience a force which will try to increase its raduis of rotation if the angular velocity is high enough to overcome the downward force of the Earth's gravity.
As the rotating platform loses velocity (due to frictional forces) the centrifugal force on the ball will also fall accordingly until it is less than the downward pull of gravity. After that the ball will roll down the incline. The key to keeping the ball 'suspended' is the velocity of rotation of the platform.
If you have a children's round-about in your local park stand on its perimeter while someone spins it round quickly and you will physically feel the force on your body and you will be compelled to lean toward the axis of rotation (in the centre). As the rotation slows you will feel the force on your body reduce accordingly, and your angle of lean will change.
The same thing happens to the ball on the platform.

 

[astrokreng]

for sharing your observation and question with us. It sounds like you witnessed an experiment demonstrating the concept of angular acceleration and gravity. In this scenario, the ball on the elevated platform is experiencing two forces: the centrifugal force from the rotation of the platform and the force of gravity pulling it down. These two forces are in equilibrium, meaning they are balanced and cancel each other out. This is why the ball does not immediately roll down the platform.

However, as the rotation continues, the centrifugal force decreases due to the decreasing radius of the rotating platform. This results in an unbalanced force, causing the ball to eventually roll down the platform. This phenomenon is known as angular acceleration, where an object experiences a change in its rotational speed.

In summary, your observation demonstrates the relationship between angular acceleration and gravity. It also highlights the importance of understanding forces and their effects on objects in motion. Keep asking questions and exploring these concepts – that's what being a scientist is all about!