Density and Pressure Flashcards
What is the formula for
density?
density = mass / volume
p = m / v
What is density measured in?
grams per centimetre cubed (g/cm^3) or kilograms per metre cubed (kg/m^3)
How can you measure an object’s
mass?
using a mass balance
What is mass measured in?
kilograms (kg) or grams (g)
How can you measure the volume of a regularly shaped object?
volume = width x height x length
v = a x b x c
How can you measure the volume of an irregularly shaped object?
by submerging the object in water and finding how much water it displaces
(volume of object = volume 2 - volume 1)
(aka the displacement method)
What is volume measured in?
m^3
How woul you carry out the
displacement method?
Take a known volume of water in a measuring cylinder and fully submerge the object. The change in volume is your object’s volume.
What is the formula for
pressure?
pressure = force / area
P = F / A
What is area measured in?
m^2
What is a
fluid?
a solid or a gas
What is the formula for
pressure due to a liquid?
pressure = density x gravitational field strength x height
P = Pgh
to find the total pressure exerted by a fluid you need to add on atmospheric pressure
What is pressure measured in?
Pascals (Pa) or Newtons per meter squared (N/m^2)
What is height measured in?
metres (m)
What is
Archimedes principle?
An object in a fluid is subject to an upward force that is equal to the weight of the fluid it displaces. This force is called upthrust. This force reduces the apparent weight of the object because the resultant force acting on it is lower.
What is the formula for
weight?
(Archimedes principle)
weight = volume x density x gravity
W = vpg
(vogue)
How do you calculate
apparent weight?
(Archimedes principle)
apparent weight = object weight - upthrust
What is the formula for
the volume of a sphere?
v = 4πr^3 / 3
What is the formula for
pressure due to gas?
(U-tube manometer)
pressure due to gas = pressure due to column of liquid + atmospheric pressure
What is the formula for
pressure due to a column of liquid?
pressure = density x gravitational field strength x height
P = pgh
(more to read and understand rather than anything else)
Explain how pumping water into and out of the buoyancy tank of a submarine affects the depth of the submarine below the surface.
[6]
Due to Archimedes principle, the amount of upthrust on the submarine will not change when water is added/removed from the tank because the amount of liquid displaced by the submarine stays the same because the submarine’s volume stays the same. So, as more water is added to the tank, the submarine’s weight will increase and may overcome the force of upthrust. This would lead the submarine to sink (and vice versa). If the water is pumped out of the tank, the amount of upthrust will overcome the submarine’s weight and the submarine will rise to the surface of the water. This concept applies across varying degrees.
[6]
all written by me I’d like to mention
What is the general shape of a
solid?
regular, fixed, holds shape
What is the general shape of a
liquid?
fluid, can change, fills bottom of container
What is the general shape of a
gas?
fills container
Can a solid be compressed?
no
(volume stays the same)
Can a liquid be compressed?
no
(volume stays the same)
Can a gas be compressed?
yes
(volume can change)
What is the general packing of atoms or molecules in a
solid?
densely packed, arranged, vibrating
What is the general packing of atoms or molecules in a
liquid?
relatively dense, molecules slide over each other
What is the general packing of atoms or molecules in a
gas?
not very dense, molecules move freely
What are the general strength of forces in a
solid?
strong forces of attraction
What are the general strength of forces in a
liquid?
relatively strong forces of attraction
What are the general strength of forces in a
gas?
weak forces of attraction
What is some evidence supporting
kinetic theory?
- crystals and crystal structure
- images from microscopes
- diffusion of gases
- brownian motion
Define
brownian motion.
the random motion of particles in suspension
Why do air molecules move
rapidly and randomly in all directions?
because they are being bombarded by other air molecules from all sides
Using the continuous movement of particles in a gas,
explain why gases exert a pressure?
- Gas particles are in constant random motion.
- The particles collide with the walls of their container, which changes their dircetion.
- A change in direction requires a force to have been exerted on them by the container.
- This means the particles exert and equal and opposite force on the container
- These forces over an area exert a pressure.
The net force caused by gas pressure is always perpendicular to the surface of the container.
What is
Boyle’s law?
p1v1 = p2v2
1 and 2 refer to the gas in two different situations
What is necessary for
Boyle’s law?
constant temperature
What is the
pressure law?
If we increase the temperature of a fixed volume of a gas we increase the pressure.
What is the atmospheric pressure at the ground?
roughly 1 x 10^5 Pa
What happens to air pressure as height changes?
as you increase in height there is less air above you, which means the air pressure decreases
(and vice versa)
What is 0K in °C?
-273°C
What is
absolute zero?
where the particles have no kinetic energy and so are not moving and exert no pressure
Define
work.
the transfer of energy by a force
