# Behaviour of a ping pong ball dropped in a can full of water.

• chirumu
In summary, the experiment involved dropping a can filled with water and a ping pong ball from a height of 1m onto pavement, first with a regular ball and then with a ball covered in vaseline. The observations showed that the regular ball bounced out of the can while the vaseline ball remained floating. The variables were constant and the independent variable was the type of ball. The normal ball adhered to the surface of the water due to its weight and surface tension, but the vaseline ball did not due to its waxy nature. The normal ball bounced out of the can due to a combination of water pressure, upwards force from the pavement, and buoyancy. It is difficult to accurately observe the movements of the falling objects without high
chirumu

## Homework Statement

I performed the following experiment in my backyard this afternoon.

A 500ml can is filled with water and a ping pong ball floats on its surface. The can is dropped from a height of 1m onto pavement. The experiment is then repeated with the exception that the second time round, the ping pong ball is covered in vaseline.

my observations:

THE NORMAL BALL:
as the can was falling the ball stayed on the surface of the water. When the can hit the ground the ball flew upwards. Water came out of the can.

THE VASELINE BALL:
as the can was falling the ball stayed on the surface of the water. When the can hit the ground the ball sort of 'fell' out of the can. From what i saw, i assume that if the system was perfect it would of stayed in the can.

I guess what I'm asking is: why did the normal ball bounce out of the can while the vaseline ball remained floating.

## The Attempt at a Solution

All variables were constant. The independant variable was the vaseline ball vs. the normal ball.

THE NORMAL BALL:
The ball falls with the same velocity as the can. There is no air resistance between the ball and water so resistance is the same as on the can. The ball adheres to the surface of the water (i ensured the ball was covered in water before performing the experiment). As the can falls the ball remains on the surface of the water due to bouyancy. When the can hits the ground it imposes a downwards force on pavement and the pavement causes an upwards force. The upwards force causes the water to move upwards taking the ball with it due to surface tension.

THE VASELINE BALL:
The ball falls with the same velocity as the can. There is no air resistance between the ball and water so resistance is the same as on the can. The ball does not adhere to the surface of the water due to its waxy organic nature. As the can falls the ball remains on the surface of the water due to bouyancy. When the can hits the ground it imposes a downwards force on pavement and the pavement causes an upwards force. The upwards force causes the water to move upwards, but the ball stays put because of surface tension so it resists the upwards force.

LASTLY:
It was really hard to keep an eye on the ball as it was falling. I kind of feel like the normal ball would of displaced more water and fallen deeper into the can on impact, then somehow a combination of water pressure (i'm not sure how to consider pressure in this case. I know that pressure would be greater at the bottom of the can), the upwards force and bouyancy caused it shoot upwards. However I'm not sure because i didnt actually see it happen.

You are showing a very good attitude at making experiments, drawing hypothesis, making variation, observing, and so on.
Said that, I think that the falling of an object is a quick movement and any naked eye observation produces rough and unmeasurable data. You'd need an high speed camera, something like 1000 frames/s, but those are expensive objects, out of reach for a domestic use.

## 1. How does the ping pong ball behave when dropped in a can full of water?

When a ping pong ball is dropped in a can full of water, it will initially sink due to its density being greater than that of water. However, as it sinks, it displaces water and creates an upward force called buoyancy. This buoyant force will eventually become equal to the weight of the ball, causing it to float at a specific level in the water.

## 2. Why does the ping pong ball float in the water instead of sinking to the bottom?

The ping pong ball floats in the water because of the upward force of buoyancy. As the ball displaces water, it creates a downward force called weight, which is equal to the ball's mass multiplied by the acceleration due to gravity. As long as the buoyant force is greater than the weight, the ball will float in the water.

## 3. How does the depth of the water affect the behavior of the ping pong ball?

The depth of the water will affect the behavior of the ping pong ball as it sinks. The deeper the water, the higher the pressure on the ball, which compresses the air inside the ball. This compression of air decreases the volume of the ball and increases its density, causing it to sink faster. The opposite is true for shallow water.

## 4. Does the temperature of the water affect the behavior of the ping pong ball?

Yes, the temperature of the water can affect the behavior of the ping pong ball. Cold water is more dense than warm water, so the ball will float higher in cold water than in warm water. Additionally, cold water can decrease the air pressure inside the ball, making it less buoyant and causing it to sink faster.

## 5. How does the shape of the ping pong ball affect its behavior when dropped in water?

The shape of the ping pong ball can affect its behavior when dropped in water. A smooth, round ball will experience less drag and sink slower than a ball with an irregular or rough surface. Additionally, a ball with a larger surface area will displace more water and experience a greater upward force of buoyancy, causing it to float higher in the water.

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