Biomechanics- Fluid mechanics Flashcards
(9 cards)
Which one of the following will increase the drag experienced by a cyclist?
A Following another cyclist closely
B Travelling at a higher velocity
C Wearing tight-fitting clothes
B
The photograph below shows Laura Kenny cycling at the Rio 2016 Olympics.
Analyse how Laura Kenny has maximised her speed in the photograph. Use Bernoulli’s principle of lift and knowledge of the factors that influence drag.
(Total 15 marks)
AO1 – Knowledge of Bernoulli’s principle of lift and factors affecting drag using simple statements
Bernoulli’s principle is to do with lift force and downforce created when air flows over an aerofoil or object. Where there is an increase in the velocity of air there is a decrease in the pressure. Where flow is fast, pressure is low and 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. There are two types of drag, surface drag and form drag. Factors that affect drag include the velocity of the body or air, the cross sectional area, the shape of the body and type of surface.
AO2 – Application of Bernoulli’s principle of lift and factors affecting drag to the cyclist
Due to the streamlined position of Laura Kenny, the air travelling over the top of her has a shorter distance to travel than the air underneath. This means the air above is travelling at a slower velocity, which therefore creates a higher pressure. This creates a downward lift force with the tyres applying more force to the track.
Drag acts in the opposite direction of motion and so will be slowing Laura Kenny down. In order to minimise the amount of drag Laura Kenny can consider the factors that affect drag including, her cross sectional area, the shape she makes on the bike and type of surface. Therefore, as shown in the photograph, Laura Kenny wears a streamlined helmet, tight clothing and adopts a streamlining position on the bike i.e. her back is parallel to the track, her arms are tucked in close to her body which all reduce form drag. To reduce surface drag the tyres are very thin on the bike and her suit is very smooth.
AO3 – Analysis / evaluation of Bernoulli’s principle of lift and factors and the impact of reducing drag to allow the cyclist to achieve a faster speed
Factors that affect drag include the speed Laura Kenny is travelling at, the cross sectional area of Laura Kenny’s body and bike, the shape of Laura Kenny and type of surface. Therefore, as shown in the photograph, Laura Kenny can reduce drag by wearing a streamlined helmet. This is beneficial because it will allow the air to pass quicker over the top of the helmet reducing the drag created which means Laura Kenny can cycle faster.
Although speed is a factor that can influence drag, Laura will use the other factors such as her clothing and body position to ensure she cycles as fast as she can therefore she won’t reduce her speed in order to reduce drag.
Credit other relevant analysis of how a cyclist can increase their speed using Bernoulli’s principle of lift and knowledge of the factors that influence drag.
Max 15 marks
Explain the methods used to reduce the forces acting on a cyclist whilst racing.
(Total 4 marks)
- Friction (between wheels and track) acts against cyclist
- Air resistance/Fluid Friction (acting against cyclist moving through air)
- Acts in opposite direction of motion
- Increases as cyclist’s speed increases
- Cyclist needs to reduce forces to achieve a higher speed/velocity
- Reduce friction by using thin / high pressured tyres
- Reduce friction by streamlining
- Creating smooth flow around cyclist / reducing turbulent flow / drag reducing profile drag / turbulence behind
- Reduce frontal / forward cross sectional area
- Reduce surface friction of air on cyclist / specialist smooth clothing / helmet
- Reduce turbulence behind cyclist / change body shape to smooth airflow behind cyclist
Explain how a high angle of attack will affect the distance travelled by the discus.
[total 3 marks]
AO1
* The discus does not travel as far/stalls (1).
AO3 (sub max 2 marks)
* A high angle of attack 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 of the discus becomes more and more separated (1).
Max 3 marks
Describe a cyclist’s use of the Bernoulli effect to increase his speed.
[total 5 marks]
Award one mark for each of the following points (max 4 marks):
* Body forms an aerofoil shape, creating angle of attack
* Air travels further under cyclist
* Air travels faster under cyclist
* Creates low pressure under cyclist
* (Bernoulli) Force formed from high to low pressure
* Bernoulli force downwards/down force
Discus is another athletic event.
Describe how a lift force can be generated by a discus in flight.
[total 4 marks]
Air molecules striking the under surface of the discus are accelerated (1) this causes a pressure difference between the upper and lower surfaces of the discus (1). This creates a pressure gradient (1) creating a lift force/Bernoulli effect (1).
Accept other relevant responses as to how a lift force can be generated by a discus in flight.
Give three sporting examples of how a swimmer can reduce drag during a race.
[total 3 marks]
* Ensuring they’re in a streamlined position (accept appropriate examples of a streamlined position) (1)
* Wearing a swimming hat. (1)
* Wearing specialised swimwear. (1)
* Removing body hair. (1)
Accept any other appropriate example of how the swimmer can reduce the effect of drag throughout a race.
Explain how a lift force is imparted to a discus during flight and explain its effects on the flightpath of the discus.
[total 5 marks]
- Discus is an aerofoil shape
- Takes on an appropriate angle of attack to the direction of motion
- Air has to travel further over the top of the discus
- Air travels faster over the top of the discus
- This creates a low pressure area on top of the discus called the Bernoulli principle
- Air tries to move from high to low pressure (creating the lift force)
- Makes flight path non parabolic/asymmetrical
- Lengthens flight path/discus travels further / is in air for longer
Analyse how an athlete can maximise the distance a discus travels.
Use your knowledge of the factors affecting horizontal displacement of projectiles and the Bernoulli principle in your answer.
[total 15 marks]
AO1 Knowledge of the factors affecting horizontal displacement of projectiles and the Bernoulli principle
* Angle of release, dependent on the height of release and height of landing of the projectile.
* Speed of release, the greater the speed of release, the greater the horizontal displacement of the projectile.
* Height of release, the greater the release height, the greater the horizontal displacement.
* The Bernoulli principle states where air flow is fast over the surface of an object pressure is low, where air flow is slow over an object pressure is high.
AO2 Understanding of how the factors affecting horizontal displacement of projectiles and the Bernoulli principle affect the flight of a discus
* Release height of discus out of the athlete’s hand is greater than the landing height.
* The faster the athlete spins in the circle the greater the speed of release.
* Height of release depends on the height of the athlete / technique.
* The discus needs to be thrown with the optimal angle of attack for the Bernoulli principle to take effect (this is between 25 and 40 degrees).
* Athlete throwing the discus will try to optimise the speed, height and angle of release as well as the angle of attack.
AO3 Analysis of the impact the factors affecting horizontal displacement of projectiles and the Bernoulli principle will have on the distance the discus travels
* (Release height of discus out of the athlete’s hand is greater than the landing height) therefore the optimum angle of release is less than 45°.
* If the angle of release is above optimal the speed of release will be slower due to air resistance meaning the discus will travel a shorter distance before landing.
* The speed of release can be increased by improving the throwers power / suitable training method.
* Taller athletes with better technique will be able to optimise horizontal displacement due to a greater height of release.
* If the angle of attack is optimal, air travelling over the top of the discuss will have further to travel, travelling faster, creating low pressure.
* Air travelling under the discuss will have less distance to travel, moving slower creating high pressure.
* Air will move from high to low pressure creating lift and optimising the distance the discus travels.
Accept any other appropriate analysis of the factors affecting horizontal displacement of projectiles and the Bernoulli principle’s impact on the distance a discus travels.
