11.3-5

Question 1

what is the force of gravity?

Answer 1

the force that any two objects attract each other

Question 2

what is the force of gravity exerted by the earth?

Answer 2

it pulls an object towards the earth’s centre

Question 3

is the force of gravity a contact force or a non-contact force?

Answer 3

non-contact force

Question 4

how would the force of gravity acting on an object change if the object’s mass increases?

Answer 4

the magnitude of the force of gravity acting on that object increases

Question 5

what is the weight of an object?

Answer 5

the force of gravity acting on the object

Question 6

how can weight be measured?

Answer 6

by using a spring balance

Question 7

what is the unit of weight?

Answer 7

newton (N)

Question 8

how does the weight change when the force of gravity acting on an object increases?

Answer 8

the weight increases

Question 9

what is the mass of an object?

Answer 9

it measures the amount of matter the object contains

Question 10

what is the unit of mass?

Answer 10

kilogram or gram

Question 11

how does the mass of an object change in different places? why?

Answer 11

it is the same because the amount of matter contained in the object is always the same

Question 12

how does the weight of an object change in different places? why?

Answer 12

it changes from place to place depending on the gravitational pull

Question 13

what is the difference between the moon’s gravitational pull and the earth’s gravitational pull?

Answer 13

the moon exerts a force of gravity on an object about one-sixth what the earth does

Question 14

what is the difference between an object’s weight on earth and its weight on the moon?

Answer 14

the object’s weight on the moon is one-sixth on the earth

Question 15

how is the weight of an object related to its mass?

Answer 15

it increases in proportion

Question 16

what is the ratio of weight to mass?

Answer 16

9.8 N/kg

Question 17

why does an object of a greater mass have a greater weight?

Answer 17

an object of a greater mass experiences a larger force of gravity and thus has a greater weight

Question 18

what is friction?

Answer 18

when an object slides or tends to slide over a surface, friction acts on the object and opposes the object’s sliding motion

Question 19

can friction act on objects that are not moving?

Answer 19

yes

Question 20

is friction a contact force?

Answer 20

yes

Question 21

what is air resistance?

Answer 21

when an object moves in air, an opposing force acts on the object

Question 22

how does the air resistance acting on the object change when the object’s speed increases?

Answer 22

the air resistance increases

Question 23

3 ways to reduce friction

Answer 23

1. use lubricants
2. separating surfaces using an air cushion
3. using rolling objects

Question 24

what are 2 examples of lubricants?

Answer 24

soapy water or lubricating oil

Question 25

how does a lubricant reduce the friction?

Answer 25

it creates a thin layer between the two surfaces, preventing them directly rubbing against each other

Question 26

how does adding a layer of air reduce the friction?

Answer 26

the air layer separates the two surfaces, preventing them from directly rubbing against each other, reducing the friction

Question 27

how can we reduce air resistance?

Answer 27

streamlining the shapes of objects

Question 28

how can we make use of friction when we are walking?

Answer 28

the friction between our shoes and the ground enables us to walk

Question 29

how can we make use of friction when we are holding a sushi with a chopstick?

Answer 29

we can hold the food because of the friction between it and the chopsticks, preventing it from falling

Question 30

how does the air resistance on the parachute help the skydiver?

Answer 30

the air resistance acting on the parachute slows the skydiver down and helps him land safely

Question 31

how do forces occur in?

Answer 31

pairs

Question 32

what are forces that act in pairs called?

Answer 32

action and reaction

Question 33

what is action and reaction?

Answer 33

newton's third law

Question 34

how do action and reaction act?

Answer 34

on different objects, in opposite direction, same magnitude