6.8 Liquid Pressure & Upthrust

Question 1

Why are liquid’s density the same everywhere?

Answer 1

They can’t be compressed

Question 2

When an object is in the water, the __________ force acting on an object is equal to the weight of fluid it has displaced. If this force is ______ to the object’s weight, then the object will float. If it is less than the object’s weight, it will sink.

Answer 2

upwards, equal

Question 3

Why does an object float?

Answer 3

It is less dense than the liquid it is in - it displaces a volume of water with a weight equal to its own weight before it’s completely submerged.

Question 4

Why does an object sink?

Answer 4

It is more dense than the liquid. It displaces a volume of water equal to its volume, but that weights less than the object. So the weight of the object is always greater than the upwards force.

Question 5

What are the factors which determine the pressure exerted by liquid? (3)

Answer 5

• The depth. At a greater depth, more pressure is exerted.
• The density of the liquid. More dense liquids exert greater pressure.
• The gravitational field strength, which is 9.8 N/m on earth.

Question 6

What are the units of pressure in a liquid?

Answer 6

Pascals (Pa)

Question 7

Upthrust is caused by:

Answer 7

The pressure on the bottom of the object being greater than the pressure on the top of the object