Lecture 32 - Friction and Traction

Question 1

what is friction

Answer 1

the force that opposes the movement of two surfaces that are in contact with one another

Question 2

what is force locking

Answer 2

between two smooth materials

friction created by pressing two surfaces together

Question 3

form locking

Answer 3

relates to the nature of the surface - material properties of traction

Question 4

u in the friction equation describes the

Answer 4

describes the traction dynamics i.e shoe - surface interaction

Question 5

Us sets the limit for what

Answer 5

sets the limit for when sliding begins,

Question 6

if the force applied exceeds U FN, the object will

Answer 6

start to slide

Question 7

once sliding occurs Us is changed to

Answer 7

Uk

Question 8

Uk governs the …

Answer 8

resistance to ongoing motion

Question 9

Us dictates the relationship between

Answer 9

your weight force and your horizontal force, dictating when you slide

Question 10

once you start to slide….

Answer 10

the coefficient changes and becomes the coefficient that describes your ability to keep sliding

(coefficient of kinetic friction - Uk, when you are sliding)

Question 11

how does the coefficient of friction modify the Fh (horizontal force) required to slide

Answer 11

if u>1 then Fh must be very high to overcome normal force

if u<1 then sliding may occur with Fh less than Fn

Question 12

what are the injury considerations in tennis

Answer 12

1. traction
2. synthetic or artificial surfaces
3. environmental conditions

Question 13

the force holding two objects toegther is the …

Answer 13

always the normal force (weight force)

Question 14

what will an incline do to normal force

Answer 14

change the effectiveness of normal force

Question 15

an incline can make it easier to initiate ..

Answer 15

sliding

Question 16

weight force is the force due to gravity, acting vertically downwards, can be split into two components : what are they

Answer 16

parallel component

perpendicular component

Question 17

what is the parallel component of weight force

Answer 17

this pulls the object down the slope and is responsible for initiating motion

Question 18

what is the perpendicular component of weight force

Answer 18

this presses the object against the surface of the incline and determines the normal force

Question 19

how can a player create advantage for themselves when trying to tackle in rugby

Answer 19

pushes up and forward

• puts normal force on an incline, offsetting perpendicular component to give themselves an advantage

Question 20

surfaces with greater translation and rotational resistance between the shoe and surface have higher…. and what is this related to

Answer 20

knee and ankle movements

related to rotational injuries such as ACL etc

and long term degeneration

Question 21

artificial / synthetic surfaces may reduce … and what does this allow

Answer 21

sliding and rotational freedom

sliding allows reduction in loading by increasing the deceleration distance

Question 22

what is the increased rate of incidence of tennis injuries on non sliding vs sliding surfaces

Answer 22

200% higher incidence

Question 23

the magnitudes of maximum static friction and kinetic friction are determined by

Answer 23

by the coefficient of friction between the two surfaces and by normal reaction force pressing the two surfaces together

Question 24

the direction of friction force always …..

Answer 24

opposes the direction of motion or motion tendency