CH : 8 - force , lever , moment of force

Question 1

what is force

Answer 1

m = force is pull or push upon a object

Question 2

force can be differentiate into 2 , what is it

Answer 2

contact force (m) = involve physical contact 
{ frictional, buoyant , normal , elastic }
non-contact force (m) = do not involve physical contact 
{ gravitational , electrostatic , magnetic }

Question 3

(M) of weight

Answer 3

effect of gravitational force

Question 4

(M) normal force

Answer 4

force that acts perpendicular to the surface of an object

Question 5

(M) of gravitational force

Answer 5

force of attraction that cause objects to fall toward the earth

Question 6

(M) of elastic force

Answer 6

force that produces when an object is stretched or compressed

Question 7

(M) of frictional force

Answer 7

force that resists movement between 2 surfaces that are in contact with each other

Question 8

(M) buoyant force

Answer 8

the thrust force that acts on obj that is floating on surface of water

Question 9

(M) of electrostatic force

Answer 9

force of attraction and repulsion between two electrostatic changes

Question 10

(M) magnetic force

Answer 10

force of attraction and repulsion in magnetic field

Question 11

(M) of electrical force

Answer 11

force that produced when electrons move through a conductor

Question 11

(M) of electrical force

Answer 11

force that produced when electrons move through a conductor

Question 12

what will happen if there is no frictional force

Answer 12

• easily to fall down

- the moving car cannot stop moving

Question 13

when we light a match { huo cai } why it is hard to rub the stick onto the box

Answer 13

due to the frictional force

Question 14

what is the direction of frictional force

Answer 14

the opposite direction of motion

Question 15

what will happen if there is no gravitational force

Answer 15

all the things will float in the air

Question 16

what is the relationship between the surface of object and frictional force

Answer 16

the rougher the surface, the bigger the frictional force

Question 17

lists the characteristics of force

Answer 17

• magnitude (M) quantity of value of measurement
• direction (M) the path that has forces that move forward
• point of application (M) is the point which a force applied an object

Question 18

what is the unit for force

Answer 18

S.I unit = newton (N)

• 1kg = 10N
• 100g = 1N

Question 19

if the weight of an object on Earth is 600N, is the weight of an object on the moon as same as the Earth

Answer 19

no, because the weight of an object depends on gravitational force.
weight of an object = 600N/6 = 100N bcs ration of earth to moon is 1 : 6

Question 20

what is the (M) of action-reaction pair

Answer 20

equal in magnitude but opposite in direction

Question 21

what is the (M) Newton’s Third Law

Answer 21

states that every action force there is a reaction force with the same magnitude but opposite direction

Question 22

what is the effect of force

Answer 22

• moving stationary objects
• stopping moving objects
• changing the direction of motion of an object
• changing the speed of an object
• changing the size and shapes of an object

Question 23

the formula of buoyant of force

Answer 23

actual weight - apparent weight

Question 24

the factor that affects the buoyant force

Answer 24

- volume of liquid displaced = volume ^ , buoyant force ^ | - density of liquid displaced = density ^ , buoyant force ^

Question 25

the factor that affects the density of the object

Answer 25

- mass of molecules - density of molecules arrangement - state of material * ** hot air is less dense than cold air

Question 26

F > W

Answer 26

object = less dense than water buoyant force = more than weight object = float

Question 27

F < W

Answer 27

object = denser than water buoyant force = smaller than weight object = submerge

Question 28

application of density

Answer 28

``` CARGO SHIP = marked with Plimsoll line function - use to determine a safe level for ship ---> density of sea water is different at different places { due to temperature & concentration of salt } ```

Question 29

(M) of lever

Answer 29

a bar that rotates on a fixed point

Question 30

FIRST CLASS LEVER

Answer 30

= L F E = small effort/force can produce bigger force or can move a large load = L and E - same direction

Question 31

SECOND CLASS LEVER

Answer 31

= F L E = small effort can produce bigger force = L and E - opposite direction

Question 32

THIRD CLASS LEVER

Answer 32

= F E L = large effort move only a small load = L and E - opposite direction

Question 33

what is a moment of force

Answer 33

turning effect of force when a force is acting on an object and rotate the object at a fixed point

Question 34

factor that affect the moment of force

Answer 34

- force that applied | - perpendicular distance from fulcrum to force

Question 35

the formula for moment of force

Answer 35

force (N) x perpendicular distance from fulcrum to force (m)

Question 36

#formula for lever calculations

Answer 36

load x distance of load from fulcrum = effort x distance of effort from fulcrum