P1.3 - Pressure Flashcards
why do balloons expand when air is blown into it? (3)
- gases move quickly in all directions
- so, they collide with the surface of the ballon
- each collision produces a force
- so, when more air is blown, more force is applied to the balloon causing it to expand
how does temp affect gas pressure? (3)
- particles gain more kinetic energy (1)
- causes more frequent collisions (1)
- makes more force on surface (1)
- more pressure
what is the unit of pressure?
Pa (Pascals)
what is the unit of force?
N (newtons)
what is the unit of area/surface area?
m^2 (meters squared)
what is the equation to work out pressure
force / area
(force over area)
what is extrapolating?
- basically ‘estimating’ what the result would be on a graph
(shown as a dotted line) - an extended dotted line downwards
what can you use to measure the pressure of a gas?
a manometer
what can you use to measure the pressure of air that is trapped in a bottle?
a pressure gauge
explain why it is dangerous to throw a canister full of pressurised gas in a fire? (3)
- the gas particles heat up (1)
- increasing the pressure within the can
- start moving quickly in all directions, exert a high force on the surface area of the canister (1)
- if canister is unable to width stand the force, it would explode (1)
explain the extent to which pressure is, or is not proportional to the temperature of a gas
- temp and pressure have a directly proportional relationship as long as the volume is constant
- the pressure of gas also depends on its volume as well as its temperature
State the direction of the force of a gas on the surface of a container
90 degrees (right angle)
If pressure is increased (within a closed system) how does the volume change?
- and explain the relationship (name)
The volume decreases
INVERSELY PROPORTIONAL
What is the equation for pressure and volume?
+ explain why
Pressure(Pa) x volume (m^3) = constant
+ since pressure and volume are inversely proportional, if you half one the other doubles, and so their product would always equal to the same amount
In terms of the particles why are pressure and volume inversely proportional?
- if you half the volume, the number of collisions per second between the gas particles and container doubles
Vice versa. If you double volume, the number of collisions per second halves
Why is there a higher atmospheric pressure at the surface compared to higher up?
Air is more dense at Earth’s surface, meaning the particles are more tightly packed together, so the particles collide more frequently.
If the force is so great (100 000N per square metre on earth’s surface), why do objects not collapse?
As there is the same pressure pushing outwards at the same time (forces are equal in all directions = equilibrium)
Why does a bag of crisps expand as it rises?
- since within the bag the air pressure is still the same as the ‘surface pressure’ - high
- but the outside has a lower pressure LESS PARTICLES PUSHING DOWN
- so force pushing outwards > force pushing inwards, so not in equilibrium
Explain why people who climb mt Everest need oxygen cylinders
- as there are less gas particles pushing down upon the other gas particles at a higher level
-so, there is a smaller pressure - but, as pressure and volume are inversely proportional, the gas particles have more space to move around in
- therefore, oxygen levels decrease per volume (so not enough for us)
OR
- gravity is weaker higher up (away from core), so pull is less = can move around easier = less density
What is the equation to calculate pressure in a liquid at a particular depth?
1) think ‘what factors would affect pressure in a liquid?’
Pressure = height x density x gravitational field strength
(Pa). (M). (Kg/m^3). (N/kg)
Why does the pressure of a liquid vary with depth?
- higher depth = more water molecules are compressed by the weight of all the water molecules above that layer
- pushes water molecules, and so has higher pressure
What is liquid pressure?
Water molecules colliding with each other, or the container
How is pressure affected by a more dense/less dense liquid?
- more dense = more mass per volume = more more weight pushing down = a higher pressure
In reality, what other factor affects a submerged objects pressure?
- the atmospheric pressure, as it also pushes down on the water, which then pushes down on more water
- and pushes down on the object
State which law reinforces the idea of an upwards force on a floating object?
Newton’s third law
- anything that is floating has an upwards force to balance its weight (remember weight is a force)
In terms of pressure, explain why objects float
- top of object = smaller force pushing downwards (lower depth = lower pressure)
- bottom of object = larger force pushing upwards (higher depth = higher pressure)
- so the pressure difference causes an upwards resultant force (so it floats)
What is the equation to calculate pressure?
Pressure = force/ area
(Pa). (N). (m^2)
What is the equation to see if an object would float?
(Pressure at bottom x area at bottom) -(pressure at top x area at top) = weight
Simply put, what factor decides whether an object would float or sink?
Whether the pressure difference with area is enough to balance the weight
If you want a heavy object (like a submarine) to float, what should you do?
- decrease the mass (lower weight acting downwards)
- increase the surface area (so it can balance the weight easier with the upthrust)
