Joe_Fox said:
alex said:
So, Joe..... Are you saying that any material or object immersed in a fluid will tend to rise through the fluid if the fluid density is greater than the material density?
The force associated with buoyancy is the difference between the weight of the displaced fluid and the weight of the immersed material surely?
Density is the amount of and object (weight or mass) there is an a given
volume (the amount of water the object displaces).
So objects which weigh a lot and don't displace much water (have a low
volume) will sink, while objects which are light and displace a lot of water
will float.
The relationship, then is how well the object will float. If it floats, it
is less dense than water, and if it sinks it is more dense than water don't you think?
You might think something like a ship is more dense than water, after all,
it is made of metal which is certainly more dense than water, but, the ship
is filled with air, which is much less dense than water, and makes up the
difference. That is why, when a ship gets a hole in it, it sinks. The
water pushes out all the air and makes the total density of the ship
greater. When the water, metal, and air inside the ship become more dense than the water outside the ship, the ship will sink, which is amazing.
The Titanic had a big hole in it.
Holes.... Now that reminds me:
A black hole is a region of spacetime from which nothing can escape, even light.
To see why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is travelling when it leaves your hand and the higher the ball will go before turning back. If you throw it hard enough it will never return, the gravitational attraction will not be able to pull it back down. The velocity the ball must have to escape is known as the escape velocity and for the earth is about 7 miles a second.
As a body is crushed into a smaller and smaller volume, the gravitational attraction increases, and hence the escape velocity gets bigger. Things have to be thrown harder and harder to escape. Eventually a point is reached when even light, which travels at 186 thousand miles a second, is not travelling fast enough to escape. At this point, nothing can get out as nothing can travel faster than light. This is a black hole.