lecture 7 Flashcards
(19 cards)
friction?
force that arises when ever a body moves, or tends to move across the surface of another
limiting friction?
there is a limit to the frictional force with which movement between two surfaces can be resisted
what is elasticity?
the ability of body returns to its original shape after being deformed
what is sliding friction?
the frictional force between 2 surfaces when there is movement between them
what influences rolling friction?
weight, radius of the rolling object, surfaces deformability, coefficient of friction
what happens when a ball hits a fixed surface?
both the ball and the surface are compressed slightly, the ball then rebounds from the surface and both bodies strive to restore to their former shape
what is direct impact?
bodies are moving in a straight line towards each other, one is static and the other is moving at a right angle
provide an example of direct impact?
goalkeeper punching away a lobbed shot
what is oblique impact?
when bodies do not collide “head on”, a bounce pass in basketball
a body travelling obliquely to a surface has what?
both vertical and horizontal and vertical velocity components with respect to the surface
what prevents injuries in impact?
use appropriate technique and equipment to reduce injuries and optimise performance tasks involving impacts
what does average force experienced depend on during momentum?
the time over which the motion changes
how do you reduce experienced force?
spread the force over a longer period of time
3 types of friction?
rolling, limiting and dynamic
what is the coefficient of restitution ?
is the measure meant of elasticity
what factors affect the coefficient of friction between 2 surfaces?
material and roughness
what happens when the surface is not horizontal?
there is an increase in friction when there is an incline
give an example of rolling friction?
surface wet or dry, ground hard or soft, length of the grass, or way it is lying
what happens to magnitude of friction when a ball is spinning prior to contact?
it is modified to rate and direction of the spin
