Question

in lec 5 prof lewin first said that the idea behind the process of drying the lettuce was the same that worked for the marble...but then he says its the concept of percieved gravity that explains the drying so which one of the ideas is actually working in drying the lettuce?

Answer 1

its the centripetal acceleration. if the force that keeps it going in a circle is absent then the object will not change direction, hence no change in velocity and no acceleration. this will make it fly straight out. that causes the water to fly out of the vessel but not the lettuce. regarding perceived gravity, i think what he meant was that the centrip accel. is so much her than g, that the body feels like it the gravitational force is along the path of the circle. i hope i attempted to help.

Answer 2

as the water droplets stick to the inner surface of utensil ,same as a astronaut comes out oh his bed thru spokes as prof explained in a space station and gradually when droplets find a way out i.e. a hole in utensil it comes out tangentially as if string is cut off.

Answer 3

what prof lewin is saying is that the centripital acceleration causes your percieved gravity. if we take the lettuce in the culinder example. the culinder is spun and that causes the lettuce to have a centripital acceleration (so that it moves in a circle). now as we know F=MA therefore if there is an acceleration there is also a force causing it. this force is actually exerted by the wall of the culinder.

now if we think about how we actually percieve weight/gravity we can see why the centripital accelaration causes us to 'percieve' gravity. when we stand on the floor our only indicatio of our weight is the force in our feet which is caused by the floor pushing back on you. therfore we can only experience gravity/ weight through another force (we cannot directly percieve gravity only indirectly). therefore the lettuce while being spun will feel a force which it will 'percieve' to be gravity. so prof lewin is really saying the same thing when he says centripital accelaration and percieved gravity (he could also say the normal reaction force from the culinder wall if he wanted to).

another thing to point out though is the drying affect is actually caused by an absence of centripital acceleration. the rest of the culinder (and the lettuce) has a centripital acceleration but the water does not since there is nothing to do the pushing or the pulling so as a consequance of the spinning the water is thrown out at a tangent to the rotation.

hope this helped (and wasn't too long)