Friction and drag

Drag - the force or forces acting to oppose the motion of an object through a fluid medium such as air or water

Key terms related to drag:
Surface -refers to the interaction between body surface and the fluid
Form - refers to resistive forces caused by shape of object or body
Wave - opposing force caused by the body or object making waves in the fluid

10.1.6 - different types of drag
Surface drag - caused by friction of a fluid acting on the outer surface of a body moving through it and slowing it down.
Smooth surface = lower drag / Rough surface = higher drag

ways how elite swimmers limit surface drag:
- shaving body hair to have a smoother surface
- Swimmer caps
- Swimsuits that have a lower drag coefficient than skin

Form drag - as the body pushes against a fluid the fluid pushes back (newtons 3rd law: every action has an equal opposite reaction)
Streamlining the shape and surface area of an object moving.
Streamlined body = less form drag / Blunt body = higher form drag

How can you limit form drag in swimming, speed skating, cycling and lunge skeleton
Swimming Speed skating
- Shaving body hair - Low/crouched position (way of skating put one leg over another)
- Swimming caps - One arm is placed behind (Slipstreaming: going behind others)
- Lower drag swimsuits - Skin-tight suit

lunge/skeleton
- Suit
- Feet first and pointed (plantar flexion)
- Board/sleds waxed

Wave drag - Caused by waves developing on the water surface determined by the amount of surface area exposed to the direction of forward movement.
- as an object pushes through the surface of a fluid, the fluid is displaced forming a wave.
- Wave drag can be reduced by avoiding motion at the interface between air and water

When a simmer dives in or turns off the wall, how do they try to limit wave drag?
- wave drag reducing lane ropes
- Pool level with deck at the side
- swim underwater as long as possible

Friction - the force exerted by a surface as an object moves across it or makes an effort to move across it

Two types of friction:

Static
- the force that resists the movement of an object which is in contact with another surface
- The force it takes to move a static object
- Resists the nation of motion

Kinetic
- The force of two objects that are sliding against each other
- The force it takes to keep a moving object moving
- Resists motions of a moving object

Higher coefficient of friction = harder to move the object

Lower coefficient of friction = easier to move the object

The coefficient of friction is a constant based on two surfaces or materials which are in contact.

Assuming an equal amount of force is applied to both it is measured on a scale of 1-0 with 0=no friction and 1=lots of friction.

Force of friction = Ff

Resistance = R

coefficient of friction = μ

μ=Ff/R

R = weight of an object x 9.81 (to give you the force in newtons)

To minimise friction you decrease the size of the coefficient

To maximise friction you increase the size of the coefficient

Advantages of friction:
- Objects can be placed in position and shaped
- Help to move the object because of friction. Frictional force helps move an object with high speed (e.g. studs)
- The ridges of our skin on our fingers enable us to grab and hold objects (e.g. in badminton players use grip to hold the racket)
- The energy lost due to friction in trying to move the object is turned into heat (e.g. in Formula 1 tires)

Disadvantages of friction:
- There is wear and tear on objects. Lubrication is used to allow the parts to move easier and prevent wear and tear (e.g. greasing up a bicycle)
- Friction makes it more difficult to move an object. Excess friction can make it difficult to slide a box across the floor or walk through deep snow.
- In roller skating, rolling shoes and a smooth surface are used to minimise friction (e.g. a wooden cycling floor)
- Excess friction means extra energy thus energy is being wasted.