Will a Basketball Sink or Float?

Perhaps you are learning about why certain objects float, while others sink. Or perhaps you are merely curious what happens to objects at home when they are thrown into a pool, say, for example, your basketball. Having never thrown it in a pool before, you might wonder whether your basketball will sink or float when it lands on top of a body of water.

When a basketball is placed on top of any body of water, it will float, not sink. This is due to the level of buoyancy a basketball has, and its lack of density. A basketball is not super dense and displaces more water, which is why it floats! 

This does not remain true for a fully deflated basketball, however, as the density of the basketball changes at this point.

Why Things Float or Sink

Have you ever considered why some things float on water, while other things sink? Rocks, for example, sink to the bottom of a pool or river, while an inflated ball, such as a basketball, floats on the surface. There are two scientific principles behind why some things float and some things sink: buoyancy and density.

Here is What Buoyancy is

Buoyancy is described as: the ability of entities or objects to float on water or in the air. The level of buoyancy an object has largely depends on two key factors: the amount of water the object is able to displace, and how much density an object has. 

The Average Buoyancy of a Basketball

A basketball is an object that contains air inside it, as well as being surrounded by air. When a basketball is placed on the surface of water, the air pressure below the ball pushes up harder than the air above the ball is able to. This pressure (the air below, and the air above pushing on one another) is what creates the buoyancy of the basketball.

It remains true that air is less dense than water, therefor hollow objects which contain air, such as a basketball, float.

If you were to remove half the air in a basketball, the ball will become less buoyant due to the decrease in pressure between the air above, below and inside the basketball. If the basketball is full of air, it will be at its most buoyant.

When a Basketball is Forced Under Water

It would take a significant amount of pressure to force a fully inflated basketball down to the bottom of a body of water. This is not physically possible for most humans to do on their own feat of strengths. You would need some kind of device to force the inflated ball under.

However, even if the water pressure below the surface were to cause any deflation in the ball, the ball would still rise to the surface despite its loss of internal volume. In fact, as it rises, it will shoot out of the water from the sheer force of being forced under when it is a buoyant object. 

What Happens When a Basketball is Deflated?

If you deflate a basketball half-way, the basketball will still float. If you deflate a basketball all the way, however, it will be at its least buoyant. Parts of the basketball skin will likely droop into the water. However, this does not mean the basketball skin will sink. 

However, if there is zero air what-so-ever in the skin of the basketball, at this point a basketball skin may begin to sink below the water. This is especially true if water replaces the air inside the basketball. Water will add weight to the basketball, cause the basketball to become dense and lose its level of buoyancy.

Is a Basketball Lighter or Heavier when Fully Inflated?

When a basketball is fully inflated it weighs more than when it is only partially inflated. This is because air contains weight and changes the volume of the basketball. To add air is to add weigh or volume to the object. To remove air, is to decrease the level of weight or volume of an object.

Using Density

Density is described as: the mass of a unit volume of a material substance. Translation? The density of an object is how much space that object takes up. In science, to discern the density of an object you divide the mass of a subject with its number of volume; D= M/V.

  • The Mass of a Basketball – a regulation NBA basketball (Spalding) has a mass of 0.625kg
  • The Volume of a Basketball – a regulation NBA basketball (Spalding) has a volume of 434 cubic inches.

The Average Density of a Basketball

The average density of a basketball ranges from 0.70/g/cm3 – 0.80g/cm3. This is what helps a basketball float. By comparison, a bowling ball’s average density ranges between 1.32-1.36g/cm3. To find the density of a basketball you divide its mass by its volume. 

Example: Basketball Density = 0.625kg/434 cubic inches.

A basketball is less dense than a bowling ball (as you can see through its calculated volume above.) This is why a basketball floats, while a bowling ball sinks.

Things That Float Vs Things that Sink

To fully grasp the concepts of buoyancy, density and an object’s volume, it is helpful to review a list of items that float and items that sink, so as to better picture what differentiates these things.

Things that Float

Here is a list of common objects that float due to low levels of density and higher levels of buoyancy.

  • A wooden log
  • A volleyball
  • Beach balls
  • Pool noodles
  • Pumpkins
  • Apples

Things that Sink

Here is a list of common objects that sink due to higher levels of density and lower levels of buoyancy.

  • A metal anchor
  • A baseball
  • Marbles
  • A bowling ball
  • Coins
  • Golf balls

Small Items Vs. Big Items

You might think that larger items would be more prone to sinking than smaller items, but this is not necessarily the case. In general, whether an object sinks or floats is not dependent upon and objects size, but rather how dense an object is and whether that density creates buoyancy or not. Take a big wooden log and a marble, for example.  Upon looking at two objects, you may think ‘surely the log will sink, and the marble will float.’ However, a log has less density per its mass than does a marble. 

On this train of thought, an objects shape is also not indicative as to whether it sinks or floats. A round object high in density will sink, just as a square or triangular object high in density will sink. 

The Key Take Away

As a general rule, a basketball will always float due to its hollow center and its low level of density, which causes it to be quite buoyant! It remains true that air is always less dense than water, therefore, hollow objects will float as opposed to sink.

If you remove an objects hollow center, fill it with water, and then drop it into a pool, at this point its volume has increased, as well as its density, and it is then likely to sink. When trying to understand which objects sink and which float, it is helpful to picture the difference in weight and density between a basketball and a bowling ball. 

When you understand that one sinks, while the other floats, you can begin to discern what other objects in your environment might sink while others might float!

If you found this post interesting, be sure to check “If the Sun Was a Basketball How Big Would the Moon Be?” & “Has a Basketball Team Ever Scored 0 Points?

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