Forces - Pressure and speed

Question 1

how to calculate pressure

Answer 1

pressure (Pa) = force / area of the surface

Question 2

what factors affect the pressure in a liquid

Answer 2

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

Question 3

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

Answer 3

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

Question 4

how does density affect the pressure in a liquid

Answer 4

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

Question 5

how does the gravitational field strength affect pressure

Answer 5

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

Question 6

what is the equation for pressure in a liquid

Answer 6

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

Question 7

what is upthrust

Answer 7

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

Question 8

what is atmosphere

Answer 8

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

Question 9

when is the atmosphere most dense

Answer 9

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

Question 10

what is the relationship between pressure and atmosphere

Answer 10

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

Question 11

Why does pressure decrease as we go higher above earth

Answer 11

• 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

Question 12

why do mountain climbers need to carry oxygen w them

Answer 12

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

Question 13

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

Answer 13

• 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

Question 14

what is the difference between speed and velocity

Answer 14

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

Question 15

what is speed

Answer 15

• the distance the object travels in a given time

Question 16

how to calculate velocity using displacement

Answer 16

displacement/time taken

Question 17

what is the typical walking speed

Answer 17

1.5m/s

Question 18

what is the typical running speed

Answer 18

3 m/s

Question 19

what is the typical cycling speed

Answer 19

6 m/s

Question 20

typical speed for a moving car

Answer 20

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

Question 21

typical speed for a moving train

Answer 21

55 m/s

Question 22

typical speed of plane

Answer 22

250 m/s

Question 23

speed of sound waves

Answer 23

330 m/s (in air)

Question 24

what is acceleration

Answer 24

the rate of change in velocity

Question 25

what is the equation for acceleration

Answer 25

acceleration = change in velocity / time

Question 26

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

Answer 26

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

Question 27

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

Answer 27

uniform

Question 28

what is an objects initial velocity if it is stationary

Answer 28

0

Question 29

How to find speed on a distance time graph

Answer 29

finding the gradient

Question 30

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

Answer 30

constant

Question 31

what is the objects speed when there is a flat line

Answer 31

stationary

Question 32

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

Answer 32

increasing speed (acceleration)

Question 33

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

Answer 33

deceleration

Question 34

how to find the gradient of a curved line

Answer 34

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

Question 35

what does the gradient tell us in a velocity time graph

Answer 35

the acceleration

Question 36

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

Answer 36

that the acceleration is constant

Question 37

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

Answer 37

that there is a constant deceleration

Question 38

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

Answer 38

that velocity is constant

Question 39

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

Answer 39

rate of acceleration is increasing

Question 40

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

Answer 40

find the area under the curve

Question 41

what can the average speed of walking etc depend on

Answer 41

- age - terrain - fitness - distance travelled

Question 42

what happens when particles collide with walls of the container

Answer 42

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

Question 43

what is the pressure of the atmosphere caused by

Answer 43

air molecules colliding with a surface

Question 44

why would a crisp packet inflate when its in an aeroplane

Answer 44

- 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

Question 45

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

Answer 45

- because the water at the bottom of the container is at a higher pressure than the water at the top

Question 46

why does the pressure of a liquid increase with depth

Answer 46

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

Question 47

how to explain why objects float or sink using an example

Answer 47

- 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)

Question 48

for an object to float, what needs to happen

Answer 48

the upthrust must equal the objects weight

Question 49

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

Answer 49

the weight of the water displaced by the object

Question 50

how will an object float

Answer 50

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

Question 51

why will an object sink in water

Answer 51

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

Question 52

difference between distance and displacement

Answer 52

- 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

Question 53

What affects the speed of sound?

Answer 53

Temperature, Sound travels faster and warmer days

Question 54

what is velocity

Answer 54

speed in a given direction

Question 55

what happens to an object moving in a circle

Answer 55

if its speed is constant, its velocity is constantly changing

Question 56

what is acceleration

Answer 56

change in velocity over a given time

Question 57

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

Answer 57

2m/s^2

Question 58

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

Answer 58

2000N