P11 Forces and Pressure Flashcards
what do particles in a gas and liquid exert on the walls of a container?
a force right angles to the walls of the container
what is a fluid?
gases and liquids
What is the formula for pressure?
P = F/A
What is the unit for pressure?
Pascal (Pa)
What is the atmosphere?
a thin layer of air around the earth
where is the atmosphere most dense?
at the surface of the earth as there are the most number of air particles
what happens to the atmosphere as altitude increases?
the atmosphere gets less dense
what is the pressure of the atmosphere caused by?
air particles colliding with a surface
why does atmospheric pressure decrease with height?
the number of air particles decreases above the surface
What increases the pressure of a column of liquid?
height
density of the liquid
gravitational field strength
why does an increase in the depth/height of a column of liquid increase the pressure?
there is a greater weight of liquid acting downwards
why does increasing density of a liquid increase the pressure?
they have a greater weight acting downwards
what is upthrust?
a resultant force acting upwards on an object due to the pressure difference at the top and bottom of the liquid
when does an object float?
when the upthrust of the object is greater than or equal to the weight
when does an object sink?
when the weight is greater than the upthrust
what links the upthrust exerted on an object and the amount of water it displaces?
the weight of the displaced water is equal to the upthrust acting on it
why can an object float in terms of the weight of water it displaces and upthrust?
if an object can displace its own weight of water, then the upthrust equals the object’s weight and it will float
why do low density objects float high in the water?
the object only has to displace a small amount of water before the displaced water’s weight equals the weight of the object.
what does an object float like if it has the same density as water?
the top surface of the object is at the surface of the water
why does an object sink?
the object cannot displace a volume of water equal to its own weight so the upthrust is less than the weight of the object so it sinks
what is pressure?
force per unit area
how do fluids exert pressure?
particles constantly collide with the surface of a container which exerts a force on the area of the surface
