fluid mechanics

Question 1

when an aerofoil is travelling what is the difference in velocity between the 2 directions the air will take

Answer 1

the air that travels over the top of the aerofoil will travel with higher velocity and underneath will have lower velocity

Question 2

when an aerofoil is travelling what is the difference in pressure between the 2 directions the air will take

Answer 2

the air travelling over the top with greater velocity will create an area with lower pressure and underneath where the air is travelling with lower velocity there will be higher pressure

air that travels quickly gains dynamic pressure and looses static pressure creating a pressure difference

Question 3

how does a discuss get upwards lift

Answer 3

because of the bernoulli principle the higher pressure underneath will cause the discuss to lift because the air will want to move to the lower pressure area

Question 4

what is lift

Answer 4

causes the object to move perpendicular to the direction of travel

enabling objects to stay in the air for longer increasing their horizontal displacement

Question 5

what is the angle of attack

Answer 5

this is the tilt of a projectile relative to air flow, it creates a difference between the airflow.

this alters the velocity of the airflow and therefore the pressure creating upward or downward lift force

Question 6

explain how a high angle of attack will affect the distance travelled by the discus (3)

Answer 6

AO1: the discus doesnt travel as far, it is stalled.

AO3: a high aoa will mean the discus produces less lift/more drag (1) as a result air begins to flow less smoothly over the top of the discus (1) meaning that air flow over the top becomes more and more separated (1)

reference to downwards lift and a switch in the air pressure gradient

Question 7

definition of drag force

Answer 7

it is the resistance force experienced when travelling through a fluid environment and acts in the opposite direction

has a negative effect on velocity

it is a combination of air resistance and friction

Question 8

what are the two types of drag

Answer 8

surface and form

Question 9

what is surface drag and what is it also known as

Answer 9

relates to the friction between the surface of of the object and the fluid environment

skin drag

Question 10

what is a fluid environment

Answer 10

liquid or gas, water or air

Question 11

how can swimmers and cyclists reduce their surface drag

Answer 11

by wearing skin tight clothing and shaving their body hair

Question 12

what is form drag

Answer 12

refers to the impact of the fluid environment on the object, relating to how streamlined the object is

Question 13

how do cyclists reduce their form drag

Answer 13

drafting which is changing the leader, Belgian tourniquets

Question 14

how do swimmers and cyclist reduce their form drag

Answer 14

by creating the smallest possible cross sectional front area

Question 15

how can sprinters reduce their form drag

Answer 15

by keeping their arms close to their body and keeping their hands flat

Question 16

what is laminar flow

Answer 16

when there is no turbulence behind the object

Question 17

what is vortex flow

Answer 17

when there is turbulence behind an object which acts to pull back the performer

Question 18

which type of flow is good which is bad

Answer 18

laminar flow is good and vortex flow is bad

Question 19

how do cyclists reduce their form drag

Answer 19

tuck in, specialised helmet and bike, reduce front cross-sectional area

Question 20

what is streamlining

Answer 20

involving shaping a body so that it can move as effectively and quickly through a fluid as possible, this creates less turbulence (vortex flow) reducing form drag and increasing speed (laminar flow)

reduces friction for a cyclist

Question 21

analyse how laura kenny has maximised her speed in the photograph (IP), use bernouliis principle of lift and knowledge of the factors that influence drag (15)

AO1:

Answer 21

BP is to do with lift force and downward force created when air flows over an aerofoil, where there is an increase in the velocity of air there is a decrease in the pressure, where flow is fast, pressure is low, where flow is slow pressure is high.

lift force is a force that acts perpendicular to the direction of travel

drag acts in the opposite direction of motion and so will slow something down.

2 types: surface and form

factors that affect drag: velocity of body or air, cross sectional area, shape of body, type of surface

Question 22

analyse how laura kenny has maximised her speed in the photograph (IP), use bernouliis principle of lift and knowledge of the factors that influence drag (15)

AO2:

Answer 22

streamline position>air over the top has shorter dist than underneath, so it travels slower = high pressure = downwards lift force with tyres applying more force to the track

drag opposite direction so slows laura down.

minimise: streamlined helmet, tight clothing, streamlined position ie back is parallel to the track, arms tucked into the body (reduce form drag)
to reduce surface drag the tyres are very thin and suit is smooth.

Question 23

analyse how laura kenny has maximised her speed in the photograph (IP), use bernouliis principle of lift and knowledge of the factors that influence drag (15)

AO3:

Answer 23

streamlining with the helmet allows air to pass quicker over the top reducing drag created = cycle faster

other factors as well as like clothing and body position ensure cycles as fast as she can so wont reduce speed in order to reduce drag

Question 24

explain how a lift force is imparted to a discus and explain its effects on the flight path of the discus (5)

Answer 24

discus is a aerofoil shape
takes on an appropriate AOA to direction of motion.
air has to travel further over the top of the discus.
air travels faster over the top of the dicus.
this creates low pressure on top called the bernoulli principle.
air moves from high to low creating lift force.
makes flight path nonparabolic.
lengthens flight path so discus is in the air for longer.

Question 25

how does the bernoulli principle work for a cyclist

Answer 25

body forms an aerofoil shape creating an AOA
air travels further and faster under cyclist.
creates low pressure under cyclist.
air forced from high to low pressure.
forces bike down increasing tyre friction with the floor.

Question 26

friction between wheels and track for a cyclist acts…

and comment on drag for a cyclist

Answer 26

against the cyclist

air resistance/fluid friction acts against cyclist
increases as their speed increases
acts in opposite direction to them

Question 27

by cyclists using high pressure tyres what benefit does this have

Answer 27

reduces friction so can achieve higher velocity