10. Friction and Drag Flashcards
What is friction?
A force that acts parallel to the interface of two surfaces that are in contact, and opposes their relative motion.
How is friction calculated?
Ff = μR
Where μ is the coefficient of friction and R is the normal reaction force.
What is the coefficient of friction?
The coefficient of friction (COF, μ) is a dimensionless scalar quantity which is the ratio of the force of friction
(The magnitude of the coefficient of friction depends on the materials in contact: steel on ice (in ice skating) has a low coefficient of friction)
What is static friction?
when the surfaces of two objects are at rest relative to one another
What is dynamic friction
when an object is moving or sliding across a surface.
Distinguish between the coefficient of static friction and dynamic friction.
when a force is applied to attempt to move a stationary object over another surface, we consider the coefficient of static friction. At some point, the force applied is sufficient to overcome the static friction and the object will begin to move. Once the object is in motion, we consider the coefficient of dynamic friction. The coefficient of dynamic friction is usually lower than the coefficient of static friction.
Explain the influence of friction on sports performance.
Consider maximizing and minimizing frictional influences in order to enhance performance.
For example:
sports shoes (including spikes/cleats) and playing surface (grass, artificial surfaces, wood)
winter sports (skiing, ice skating)
use of a golf glove
cycling on an indoor sloping velodrome.
Define drag
Drag is the force or forces acting to oppose the motion of an object through a fluid medium such as air or water
Outline surface drag
As a body moves through a fluid, its outer surface catches a layer of the fluid nearby, slowing it down compared to the fluid further away and so causing drag. This can be minimized by changing the surface to reduce the interaction between surface and fluid.
Example: The use of shark-skin suits in swimming or shaving the swimmer’s body to make it smooth.
Outline form drag
As a body pushes against a fluid, the fluid pushes back (action and reaction). By streamlining the body and minimizing the surface area facing the direction of the motion, this type of drag is reduced.
Its caused by the body and the object
Example: Cyclists adopting a low profile position
Outline wave drag
When a body moves along the surface of a fluid (usually water) some fluid is displaced to form a wave. These waves cause additional forces that oppose motion. Wave drag can be reduced by avoiding motion at the interface between air and water.
Example: Swimming underwater for as long as is allowed at the start of a race.
