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AQA Physics GCSE > Forces - Pressure and speed > Flashcards

Forces - Pressure and speed Flashcards

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1
Q

how to calculate pressure

A

pressure (Pa) = force / area of the surface

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2
Q

what factors affect the pressure in a liquid

A
  • gravitational field strength
  • weight of the water above the object
  • molecules surrounding the object colliding
  • density of liquid
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3
Q

how does the weight of water above an object affect the pressure in a liquid

A
  • if the object moves deeper, the pressure due to weight will increase, as there would be more water above the object
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4
Q

how does density affect the pressure in a liquid

A

the denser the liquid, the larger the mass per unit volume, so the larger it’s weight would be

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5
Q

how does the gravitational field strength affect pressure

A

it is what determines the weight of a given mass, so a bigger gfs would mean a larger weight

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6
Q

what is the equation for pressure in a liquid

A

pressure = height of the column if liquid x density of liquid x gravitational field strength

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7
Q

what is upthrust

A

when an object has a larger upwards force from the bottom than it has a downward force from the top

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8
Q

what is atmosphere

A

a thin layer of gases that surround the Earth, made up of mostly nitrogen, oxygen, greenhouse gases

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9
Q

when is the atmosphere most dense

A

at the surface of the Earth
(at the earths surface there are the greatest number of air molecules in a given volume)

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10
Q

what is the relationship between pressure and atmosphere

A

the further away from the Earth you get, the lower the pressure, as density decreases

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11
Q

Why does pressure decrease as we go higher above earth

A
  • at ground/sea level, there are a lot more particles around the object,so there will be more frequent collisions with the surface of the object, and if there are more collisions, there’ll be a greater force overall
  • an object at sea/ ground level is at the very bottom of the atmosphere, so it’ll have a huge weight pressing down on it, and since weight is just a different force, it will contribute to its pressure
  • the object in the air will have fewer particles above it so the force of weight will be smaller
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12
Q

why do mountain climbers need to carry oxygen w them

A

because the air is so thin, air pressure is too low

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13
Q

what factors affect whether or not an object will float or sink

A
  • whether or not the force of upthrust is greater than the force of weight, if upthrust is greater, object will float, if weight is greater, object will sink
  • the density of an object - a denser object will sink whilst a less dense object will float
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14
Q

what is the difference between speed and velocity

A

speed is a scalar quantity, meaning it only has magnitude
eg - 4m/s

however velocity is a vector quantity with both magnitude and direction
eg- 55m/s BACKWARDS

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15
Q

what is speed

A
  • the distance the object travels in a given time
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16
Q

how to calculate velocity using displacement

A

displacement/time taken

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17
Q

what is the typical walking speed

A

1.5m/s

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18
Q

what is the typical running speed

A

3 m/s

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19
Q

what is the typical cycling speed

A

6 m/s

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20
Q

typical speed for a moving car

A

25 m/s on a motorway
13 m/s on a main road

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21
Q

typical speed for a moving train

A

55 m/s

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22
Q

typical speed of plane

A

250 m/s

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23
Q

speed of sound waves

A

330 m/s (in air)

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24
Q

what is acceleration

A

the rate of change in velocity

25
Q

what is the equation for acceleration

A

acceleration = change in velocity / time

26
Q

why can we only ever find the average acceleration, and not the exact

A

because over a period of time, an objects acceleration may have varied, rather than being the same

27
Q

what words do we use to describe an object moving at constant acceleration

A

uniform

28
Q

what is an objects initial velocity if it is stationary

A

0

29
Q

How to find speed on a distance time graph

A

finding the gradient

30
Q

what is the objects speed when there is a straight diagonal line

A

constant

31
Q

what is the objects speed when there is a flat line

A

stationary

32
Q

what is the speed when the line gets steeper on a distance time graph

A

increasing speed (acceleration)

33
Q

what does a decrease in gradient in a distance time graph show

A

deceleration

34
Q

how to find the gradient of a curved line

A
  1. draw a tangent
  2. pick two points and divide the rise over run
35
Q

what does the gradient tell us in a velocity time graph

A

the acceleration

36
Q

what does a constant positive gradient tell us in a velocity - time graph

A

that the acceleration is constant

37
Q

what does a constant negative gradient tell us in a velocity time graph

A

that there is a constant deceleration

38
Q

what does a flat line tell us on a velocity time graph

A

that velocity is constant

39
Q

what does it mean when the line is getting steeper on a velocity time graph

A

rate of acceleration is increasing

40
Q

how do we find the distance travelled on a velocity time graph

A

find the area under the curve

41
Q

what can the average speed of walking etc depend on

A
  • age
  • terrain
  • fitness
  • distance travelled
42
Q

what happens when particles collide with walls of the container

A

they exert a force which acts at right angles to the wall (against the normal)

43
Q

what is the pressure of the atmosphere caused by

A

air molecules colliding with a surface

44
Q

why would a crisp packet inflate when its in an aeroplane

A
  • at ground level, the air pressure inside the bag is the same as the air pressure outside the bag
  • when aeroplanes are flying, the air pressure inside the cabin is kept at a slightly lower level than the air pressure on the ground
  • this means that the air pressure inside the bag is now greater than the air pressure inside the cabin, this causes the bag to inflate
45
Q

when we place holes in a container, why does the bottom hole push out water the furthest

A
  • because the water at the bottom of the container is at a higher pressure than the water at the top
46
Q

why does the pressure of a liquid increase with depth

A

because as the depth increases, there is a greater weight of liquid acting downwards

47
Q

how to explain why objects float or sink using an example

A
  • if an object is immersed in a liquid, the bottom of the object is at a greater depth than the top of the object
  • this means the bottom of the object experiences a larger pressure than the top
  • because of this, there is a larger force acting on the bottom of the object than the top (there’s a resultant force acting upwards)
48
Q

for an object to float, what needs to happen

A

the upthrust must equal the objects weight

49
Q

the size of the upthrust acting on the object is the same as…

A

the weight of the water displaced by the object

50
Q

how will an object float

A

if it can displace its own weight of water and the upthrust is equal to its weight

51
Q

why will an object sink in water

A

the object cannot displace a volume of water equal to its own weight, so it sinks
- therefore the weight of the object is greater than upthrust so the object sinks

52
Q

difference between distance and displacement

A
  • distance tells us how far an object moves
  • does not involve direction

DISPLACEMENT - tells us the distance that an object moves in a straight line from the start point to finish and must include direction

53
Q

What affects the speed of sound?

A

Temperature, Sound travels faster and warmer days

54
Q

what is velocity

A

speed in a given direction

55
Q

what happens to an object moving in a circle

A

if its speed is constant, its velocity is constantly changing

56
Q

what is acceleration

A

change in velocity over a given time

57
Q

what is the typical acceleration from a main road to a motorway

A

2m/s^2

58
Q

what would be the force required to move a family car from a main road to a motorway

A

2000N

AQA Physics GCSE (38 decks)

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