Why do stones bounce off the water?

In summary, objects bounce off the surface of water or other materials because of the way they interact with the media. Unlike light or toy cars, which can pass through or glide over a medium, objects like stones or bullets must displace the medium, causing it to create a sloped ramp for the object to bounce off of. This is why a stone will bounce off of water, and why bombs were able to be bounced during World War II. This is different from the way light or toy cars behave, as they are able to pass through or glide over the medium without displacing it.
  • #1
GiTS
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Why does a stone bounce off the surface of the water?

Why does a bullet bounce off of the surface when it strikes a material at an angle?

When I was learning about why glass water bend light, the use of a toy car rolling over different surfaces was used. The slowing down of one side of the car made it steer in that direction. Likewise, light acts similarly when striking glass at an angle.

So why don't other objects do this? When you try and bounce a stone off the water, the stone hitting the surface of the water should slow down causing it to steer into the water.

Same thing when a bullet hits the surface of anything it can go through, it should steer into the slower medium.

So why do they bounce off instead?

And for that matter, why do things bounce? I never got ho Newton's cradle worked.

Personally, I think it's witchcraft.
 
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  • #2
GiTS said:
When I was learning about why glass water bend light, the use of a toy car rolling over different surfaces was used. The slowing down of one side of the car made it steer in that direction. Likewise, light acts similarly when striking glass at an angle.

So why don't other objects do this?

Some do. It depends on the shape. A non spinning cube thrown at the water surface at an oblique angle will flip over forward, because the bottom is slowed more. Just like you say. Initial rotation around the vertical axis can stabilize an object and prevent the steering into the water, but if the object is symmetrical enough, this doesn't matter. A sphere can bounce off well.

GiTS said:
When you try and bounce a stone off the water, the stone hitting the surface of the water should slow down causing it to steer into the water.
A flat or even a roundish stone deforms the water surface such, that it forms a sloped ramp, on which the stone glides forwards & upwards:
http://en.wikipedia.org/wiki/Stone_skipping#Scientific_explanation
http://arxiv.org/pdf/physics/0210015v1

In WW2 they even bounced bombs. Conventional ones:
http://en.wikipedia.org/wiki/Skip_bombing
And special ones, that were initially spinning backwards:
http://en.wikipedia.org/wiki/Bouncing_bomb

ETA: Ultimately the main difference to the light & toy cart models you mentioned is how the object interacts with the media. Unlike in your examples the stone must actually displace the medium to move through it, and the boundary between the two media is not static.
 
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  • #3
Thank you A.T. for your conclusive and complete answer. My curiosity is satiated for today :approve:
 

1. Why do stones bounce off the water?

Stones bounce off the water due to the surface tension of the water. When an object, such as a stone, hits the water, it creates a small depression in the surface of the water. The surface tension of the water then pulls the water molecules together, causing the depression to bounce back and the stone to bounce off.

2. What makes some stones bounce higher than others?

The height of a stone's bounce is determined by its size, shape, and density. Smaller and flatter stones tend to bounce higher because they have less surface area and weight, allowing them to be propelled more easily by the surface tension of the water. Heavier and rounder stones have more weight and surface area, making it harder for them to overcome the surface tension and bounce as high.

3. Can all stones bounce off water?

Technically, all stones are capable of bouncing off water. However, some stones may be too heavy or too porous to create a significant depression in the water and therefore may not bounce as high. Additionally, very light or flat stones may not have enough weight or surface area to overcome the surface tension and bounce at all.

4. Why do stones sometimes sink instead of bouncing?

Stones may sink instead of bouncing if they are too heavy, too porous, or have a shape that does not allow them to create a significant depression in the water. They may also sink if they hit the water at a certain angle, causing them to break through the surface tension instead of bouncing off it.

5. Is there a limit to how many times a stone can bounce off the water?

There is no set limit to how many times a stone can bounce off the water. However, as the stone bounces, it loses energy due to friction and air resistance, which may cause it to eventually sink. The height of each subsequent bounce will also decrease as the stone loses energy, until it eventually stops bouncing altogether.

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