Linear Kinetics (Forces)

Question 1

What is Newton’s 1st law?

Answer 1

an object at rest or moving at a constant velocity at a straight line will stay that way unless acted upon by a external force

Question 2

What is Newton’s 2nd law?

Answer 2

The acceleration of a body is proportional to, and takes place in the direction in which the force acts. It is also inversely proportional to the body’s mass
F = ma

Question 3

What is Newton’s 3rd law?

Answer 3

• for every action there is an equal and opposite reaction
• for every force that is exerted by one body on another, there is an equal opposite force exerted by the second body on the first

Question 4

What is friction?

Answer 4

• force that resists the sliding of 2 objects in contact
• vector quantity
• opposite of sliding potential
• parallel to surfaces in contact

Question 5

What is normal force?

Answer 5

• vertical component (gravity) acts downwards

- ground reaction (normal) force acts upwards

Question 6

What is friction force?

Answer 6

• horizontal component: acts parallel to surface

- opposite to applied force (and to potential sliding direction)

Question 7

What is static friction?

Answer 7

2 surfaces are not sliding, but have the potential for movement

Question 8

What are the 3 factors that affect static friction?

Answer 8

• texture of surfaces
• weight of block
• applied force

Question 9

As friction increases, motive force needs to _____.

Answer 9

Increase

Question 10

What is the coefficient of friction (μ)?

Answer 10

• the proportion of friction force resisting the sliding motion of the object to the normal force holding the objects together
• a constant for any 2 surfaces
• how difficult it is to move a given surface over another surface

Question 11

How does texture affect static friction?

Answer 11

• grooves, scratches, and pores interlock/interact with texture on the other surface and impede motion
• the more interactions between the 2 surfaces, the higher the value of μ

Question 12

What is the value of μ for a totally frictionless interaction?

Answer 12

0.00

Question 13

What is kinetic friction?

Answer 13

• sliding surfaces

- grooves/pores “bumping”

Question 14

What is rolling friction?

Answer 14

• occurs when 1 surface is rolling over another
• ## still depends on coefficient of friction and normal force

Question 15

Coefficient of rolling friction is much ____ (less/more) than that of static of kinetic friction.

Answer 15

less

Question 16

Rolling friction is actually a specialized case of ____ friction.

Answer 16

• static

- trying to avoid sliding, want to maintain static friction

Question 17

What is the general term for a force that is perpendicular to friction?

Answer 17

Normal force

Question 18

What are the 3 types of friction?

Answer 18

• static
• kinetic
• rolling

Question 19

What is momentum?

Answer 19

• momentum of a body is a product of its mass and velocity
• momentum = mv
• vector quantity

Question 20

What are the units for momentum?

Answer 20

kg m/s or Ns

Question 21

What is the conservation of momentum?

Answer 21

• The total momentum of any given system will remain constant in the absence of any external forces
• the momentum prior to an action is the same as the momentum following the action

Question 22

What is impulse?

Answer 22

• constant force (F) x time (t) is called the impulse of the force
• the impulse of a force is equal to the change in momentum which it produces
• relates to Newton’s second law

Question 23

The best shock absorption technique is (relating to impulse):

Answer 23

decrease force over increased time (landings)

Question 24

The best way for abrupt change of direction is (relating to impulse):

Answer 24

increase force over decreased time

Question 25

The longer the time or larger the applied force, the ______ the change in velocity of body receiving force (duration of force application).

Answer 25

greater

Question 26

Energy transfers are not 100% efficient. Where does this loss of kinetic energy (energy due to motion) go?

Answer 26

- sound - heat - absorption by deformation of the bodies involved

Question 27

What are elastic collisions?

Answer 27

bodies involved separate after collision

Question 28

What happens in a perfectly elastic collision?

Answer 28

momentum and kinetic energy is conserved

Question 29

What are inelastic collisions?

Answer 29

- at least one body deforms | - bodies involved do not separate

Question 30

What is elasticity?

Answer 30

the tendency of an object to return to its original shape once it has been deformed

Question 31

What are the 2 classifications of elasticity?

Answer 31

- elastic impacts | - inelastic impacts

Question 32

What is the degree of elasticity?

Answer 32

coefficient of restitution (e)

Question 33

e is determined by...

Answer 33

- composition of the object - composition of the surface of the object - temperature

Question 34

The value of e ranges from...

Answer 34

0 (inelastic) to 1.0 (perfectly elastic)

Question 35

What are the 2 types of impacts to consider?

Answer 35

- direct | - indirect

Question 36

What are direct impacts?

Answer 36

when objects collide head on

Question 37

What are indirect impacts?

Answer 37

when objects collide at an angle

Question 38

_____ impacts are the ones we most commonly encounter in sports.

Answer 38

indirect

Question 39

For indirect impacts, the most important relationship to consider is that between the ______of ______ and ________. It is always measured from the _____.

Answer 39

- angles of incidence and reflection | - perpendicular

Question 40

The angle of reflection depends on:

Answer 40

- the elasticity of the object - the level of friction at the contact point - the amount of spin on the object

Question 41

What happens during direct contact?

Answer 41

outcome is usually spectacular and the deformation involves one or all of the colliding bodies

Question 42

Define pressure.

Answer 42

force (F) distributed over a given area (A)

Question 43

What are the units for pressure?

Answer 43

N per square m^2 or Pascals (Pa)

Question 44

How should you decrease pressure for landing pads?

Answer 44

increase area