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OCR GCSE P1-P5 > P1.3 - Pressure > Flashcards

P1.3 - Pressure Flashcards

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1
Q

why do balloons expand when air is blown into it? (3)

A
  • 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
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2
Q

how does temp affect gas pressure? (3)

A
  • particles gain more kinetic energy (1)
  • causes more frequent collisions (1)
  • makes more force on surface (1)
  • more pressure
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3
Q

what is the unit of pressure?

A

Pa (Pascals)

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4
Q

what is the unit of force?

A

N (newtons)

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5
Q

what is the unit of area/surface area?

A

m^2 (meters squared)

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6
Q

what is the equation to work out pressure

A

force / area

(force over area)

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7
Q

what is extrapolating?

A
  • basically ‘estimating’ what the result would be on a graph
    (shown as a dotted line)
  • an extended dotted line downwards
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8
Q

what can you use to measure the pressure of a gas?

A

a manometer

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9
Q

what can you use to measure the pressure of air that is trapped in a bottle?

A

a pressure gauge

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10
Q

explain why it is dangerous to throw a canister full of pressurised gas in a fire? (3)

A
  • 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)
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11
Q

explain the extent to which pressure is, or is not proportional to the temperature of a gas

A
  • 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
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12
Q

State the direction of the force of a gas on the surface of a container

A

90 degrees (right angle)

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13
Q

If pressure is increased (within a closed system) how does the volume change?
- and explain the relationship (name)

A

The volume decreases

INVERSELY PROPORTIONAL

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14
Q

What is the equation for pressure and volume?

+ explain why

A

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

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15
Q

In terms of the particles why are pressure and volume inversely proportional?

A
  • 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

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16
Q

Why is there a higher atmospheric pressure at the surface compared to higher up?

A

Air is more dense at Earth’s surface, meaning the particles are more tightly packed together, so the particles collide more frequently.

17
Q

If the force is so great (100 000N per square metre on earth’s surface), why do objects not collapse?

A

As there is the same pressure pushing outwards at the same time (forces are equal in all directions = equilibrium)

18
Q

Why does a bag of crisps expand as it rises?

A
  • 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
19
Q

Explain why people who climb mt Everest need oxygen cylinders

A
  • 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
20
Q

What is the equation to calculate pressure in a liquid at a particular depth?
1) think ‘what factors would affect pressure in a liquid?’

A

Pressure = height x density x gravitational field strength
(Pa). (M). (Kg/m^3). (N/kg)

21
Q

Why does the pressure of a liquid vary with depth?

A
  • 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
22
Q

What is liquid pressure?

A

Water molecules colliding with each other, or the container

23
Q

How is pressure affected by a more dense/less dense liquid?

A
  • more dense = more mass per volume = more more weight pushing down = a higher pressure
24
Q

In reality, what other factor affects a submerged objects pressure?

A
  • the atmospheric pressure, as it also pushes down on the water, which then pushes down on more water
  • and pushes down on the object
25
Q

State which law reinforces the idea of an upwards force on a floating object?

A

Newton’s third law

  • anything that is floating has an upwards force to balance its weight (remember weight is a force)
26
Q

In terms of pressure, explain why objects float

A
  • 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)
27
Q

What is the equation to calculate pressure?

A

Pressure = force/ area
(Pa). (N). (m^2)

28
Q

What is the equation to see if an object would float?

A

(Pressure at bottom x area at bottom) -(pressure at top x area at top) = weight

29
Q

Simply put, what factor decides whether an object would float or sink?

A

Whether the pressure difference with area is enough to balance the weight

30
Q

If you want a heavy object (like a submarine) to float, what should you do?

A
  • decrease the mass (lower weight acting downwards)
  • increase the surface area (so it can balance the weight easier with the upthrust)

OCR GCSE P1-P5 (14 decks)

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