M3.2 forces in action

Question 1

what is centre of gravity

Answer 1

teh point where we assume all of the weight of a object

Question 2

where is the centre of gravity for objects of unifrom density

Answer 2

the geometric centre

Question 3

how to find the centre of gravity for regular objects

Answer 3

fold object
open and fold on a different plane
intersection point is COG

Question 4

irregular objects

Answer 4

hang object from a wire and clamp stand
hang a plumb line infront of the object
draw a line from the string
repeat on a different plane intersection = COG

Question 5

define equilibrium

Answer 5

the net moments on an object is 0 and the net forces on an object are 0
not moving or rotating

Question 6

define moment

Answer 6

moment is a turning effect either clockwise or anti-clockwise

Question 7

how to calculate moments at a angle

Answer 7

calculate the triangle length to the pivot (make a triangle with force distance from pivot and x(perpendiular to the force)) X to distance from pivot angle should be equal to the angle the force is at use triangle rules to prove etc

Question 8

how and when can you take a moment at a certain point

Answer 8

when a system is in equilibrium because no matter where the system pivots teh resultant moments and forces are 0

Question 9

define a couple

Answer 9

forces tht produce rotation and not movement
i.e two equal forces an equal distance from the pivot in opposite directions

Question 10

define fluids

Answer 10

a state where particles are in constant random motion
gasses or liquids

Question 11

what is archemides principle

Answer 11

upthrust is equal to the weight of the water displaces
(if ever confused look more deeply in the one note)

Question 12

what is upthrust on a floating object

Answer 12

upthrust must equal weight of the object
wieght of the object = weight of displaced fluid

Question 13

state the principle of moments

Answer 13

for a system in equilibirum the sum of the clockwise moments is equal to the sum of the anticlock wise moments

Question 14

When calculating pressure on a hollow tube how with some mass on top how would you do that

Bonus what about if internal radius (r)&raquo_space; Thickness (t)

Answer 14

calculate weight of the mass
then do force/area in contact
so mg/(π((r+t)^2-r^2)) because area of the cross section including the thickness subtract the area of cross section without the thickness
Just the are of the thickness

mg/(π(r^2+2rt+t^2)-(r^2))
mg/(π(2rt+t^2))

if r»t t^2 is irrelevant so goes it mg/π2rt

Crazy story this was a one mark multiple choice so idk man might be worth a skip

Question 15

When a 4 wheel drive car or a bike jumps over a gap from a ramp what may affect its trajectory

Answer 15

front wheel will leave first so back wheel would cause a moment and turning force to the vehicle and possibly lower its angle of trajectory

air resistance may slow down the vehicle

takes longer to cross the gap due to this