Unit 10 Flashcards
Describe friction
the force that resists relative motion between two bodies in contact. The force you need to drag one object across another.
The value of the force of friction, Ff is
calculated
using:
Ff = μR
Where μ is the coefficient of friction
and R is the normal reaction force.
Describe the coefficient of friction.
The coefficient of friction (μ) is a constant based on the two surfaces/materials which are in contact.
The coefficient of friction depends on the materials used. As an example, ice on steel has a low coefficient of friction – the two materials slide past each other easily – while rubber on pavement has a high coefficient of friction – the materials do not slide past each other easily.
They are measured on a scale of 0-1 (no units).
0 = No friction
1 = Lots of friction
Distinguish between the coefficient of static friction and dynamic friction
Static Friction - the friction between two objects when objects are not moving (the force
needed to start the movement)
ex. between a tennis racket and the hand
ex. between the shoe and the ground when running
Dynamic Friction - the friction between two objects when one or both of the objects are
moving (force maintaining the movement)
ex. skis gliding across the snow
Explain the influence of friction on sports performance
Advantages
- good in sports such as sprinting because it prevents feet from slipping on the surface
- frictional forces help to move the object by friction (ex. spikes to run fast or studs in football)
- with friction, the ridges in our skin can helps us grab objects and hold on to them (ex. gripping a badminton/tennis racket)
Disadvantages
- bad in sports such as skiing because you want minimal friction in order to slide and accelerate (waxing skis can help reduce friction)
- friction makes it more difficult when one has to move and object (excess friction can make it difficult to slide a box across the floor or walk through deep snow)
- excess friction = extra energy, therefore energy is being wasted
Define drag
Drag - the force or forces acting to oppose the motion of an object through a fluid medium
such as air or water.
- water is harder to push through than air
Talk about surface drag and how it can be minimized
Surface Drag - between the body and the fluid- when swimming, the water must move around your body and limbs
↳ a thin layer of water next to the body actually sticks to it, and moves with it causing up to 30% resistance
To reduce surface drag athletes can:
- wear tight-fitting clothing made of a smooth fabric
- streamlined headgear
- shave off body hair to improve their ability to feel the water and coordinate
movements
State the different types of drag
Form, Surface and Wave
Talk about form drag and how it can be minimized
Form Drag - refers to resistive forced caused by the shape of an object or body- shape, smoothness and orientation of the body can all affect a cyclist’s form drag
↳ crouching while cycling can lower resistance by 30%
↳ swimming with your head up makes you unstreamlined and causes form drag
↳ whereas swimming in a streamline position reduces water and air resistance and
therefore reduces form drag
To reduce form drag athletes can:
- change the frame designs on bikes
- maintaining a streamlined position in swimming
- crouching while cycling
Talk about wave drag and how it can be minimized
Wave drag- opposing force caused by the body or object making waves in the fluid
- a swimmer will create waves within the fluid which will resist the motion of an object
- the size of the waves will depend on how your body is positioned in the water
- if the swimmer gets too close to the surface of the water the wave drag will be bigger, whereas if they are further away from the surface of the water, the waves will be smaller, meaning there is less drag
Discuss factors that influence the amount of drag in sports
- Clothing for swimmers and skiers that is tighter can reduce drag (surface)
- In velodrome cycling, the shape and structure of the helmet and bicycle reduces drag (form)
- Streamlining (in cycling, adopting a crouch position and wearing skin suits increases speed and reduces drag) (wave/form)
- How close or how far a swimmer is from the surface of the water (wave)
Annotate a free-body diagram showing the direction of relevant forces acting on an
athlete or object in sports
Look at wix website for reference
