u2: dynamics

Question 1

define dynamics

Answer 1

study of motion including the forces involved

Question 2

define force

Answer 2

• a push or pull
• its range is infinite
• distance decreases impact

Question 3

inertia

Answer 3

• matter maintains its state of motion
• bigger mass = bigger inertia

Question 4

gravity

Answer 4

• weakest force
• has infinite range

Question 5

newton’s first law of motion

Answer 5

if there is no net force on an object, then the object will maintain a state of rest or constant velocity

Question 6

newton’s second law of motion

Answer 6

if there is a net force acting on an object, then the object will accelerate in the direction of the net force. the acceleration is directly proportional the net force and inversely proportional to the object mass

Question 7

newton’s third law of motion

Answer 7

if object A exerts a force on object B, then object B exerts an equal and opposite force on object A

Question 8

equation for first law

Answer 8

if Fnet=0, then object is at rest or constant velocity

Question 9

equation for second law

Answer 9

• if Fnet≠0, then acceleration is present
• F=ma so F∝a

Question 10

equation for third law

Answer 10

F(AonB) = - F(BonA)

Question 11

when finding gravity using Fg=mg, wht is the direction and units? how about normal force?

Answer 11

• units: N
• direction [twds centre of earth]
• normal force: same magnitude, change direction to [opposite centre of earth]

Question 12

if you’ve found Fg with Fg=mg, and u need to find normal force, how do u explain it?

Answer 12

• F(nety)=0 and F(nety) = Fg + FN
  OR
• forces are balanced, so Fg = -Fn

Question 13

define net force

Answer 13

the sum of all forces acting on an object

Question 14

how do we find net force in 2D

Answer 14

1. find net force in each coordinate direction
2. combine to find overall force

Question 15

how do we pick a coordinate system?

Answer 15

direction of motion/attempted motion must be aligned with one of the coordinate directions

Question 16

how do we typically represent direction in a horizontal plane?

Answer 16

traditional direction (NESW)

Question 17

why is finding net force important

Answer 17

it tells us:
- type of motion
- direction of motion

Question 18

net force conditions

Answer 18

• unabalanced: F(net)≠0, so a is present
• balanced: F(net)=0, so obj at rest or constant velocity

Question 19

condition and summation

Answer 19

• if F(net)=ma, F(net)=Fa+Fb+Fc
• if F(net)=0, F(net)=Fa+Fb+Fc

Question 20

what direction does Fair go?

Answer 20

• opposite of motion
• I.e. if ball goes up, Fair is down

Question 21

if something is being pulled across smooth ice/surface, what does it mean?

Answer 21

no friction

Question 22

if a child is pulling a sled, with the pulling rope going diagonally up, how do u draw the coordinate system?

Answer 22

• force is diagonal, but motion is horizontally straight
• so, coordinate is normal, with X pointing in motion