Block moving on a frictionless loop

AI Thread Summary
To determine the minimum height from which a block can be released to complete a loop on a frictionless slide, it is essential to consider the forces acting on the block at the top of the loop. The block must maintain a minimum speed to ensure it remains in contact with the surface, which is influenced by gravitational force. The discussion highlights confusion about the need for a force counteracting gravity, emphasizing that vertical acceleration at the loop's peak can suffice. Understanding the dynamics of circular motion is crucial, as demonstrated by real-life examples like roller coasters. The key takeaway is that maintaining sufficient speed at the top of the loop is vital for the block's contact with the slide.
phosgene
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Homework Statement



A block moves on the frictionless slide shown in the diagram. What is the minimum height from which the block can be released if it is to complete the loop without leaving the surface of the slide? (Assume that the dimensions of the block are small compared to R, and that there is no energy associated with rotational motion of the block.) Hint: Think about the minimum speed of the block at the top of the loop if it is to remain in contact with the surface.

physicsdiagram-1.png


Homework Equations



?

The Attempt at a Solution



I have no idea at all! I mean, for the block to stay in contact with the top of the loop, it would need some kind of force to counteract gravity. Even if it was moving really fast, wouldn't the slightest influence of gravity pull it away from the loop? But I can't think of any force acting against gravity. Well, I'm pretty sure that this reasoning is wrong, because I've seen something like this done in real life. So I'm totally stuck..
 
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haven't you ever seen a rollercoaster go around a loopdeloop? Or swinging water over your head in a bucket and it not coming out? What force is applied to something that is moving in a circle?
 
phosgene said:
But I can't think of any force acting against gravity.
There does not necessarily have to be a force acting against gravity at the top of the loop if the object is accelerating vertically downward at that point. Is it?
 

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