F2 - SEM2 - Force and motion - 11.4 Friction and air resistance

Question 1

T or F

Friction is a contact force

Answer 1

True

Friction is a contact force

Question 2

When an object slides over another object, where does the friction arise? What is the direction of friction?

Answer 2

The friction arise between two surfaces that are in contact with each other
The friction arise to oppose the motion

Question 3

What is the effect of friction on the motion?

Answer 3

Slow down or stop the motion

Question 4

Overlap the pages of 2 books alternatively and lift up one of the book. Why both books are lifted up?

Answer 4

Friction between the pages prevent the sliding motion of another book

Question 5

Insert a chopstick into a bottle of rice until it reach the bottom and the pull up the chopstick. Why the bottle of rice is lifted up?

Answer 5

Friction between the chopstick and the rice prevents the sliding motion

Question 6

Name one tools that can be used to measure the friction

Answer 6

Spring balance

Question 7

T or F

Pull an object on table,
Before the object starts to move, the pull force is less than the friction
When the object moves, the pull force is same as the friction

Answer 7

False

Before the object starts to move, the pull force is same as the friction
When the object moves, the pull force is greater than the friction

Question 8

Besides affecting the motion of the object, what are other effects that friction can produce when an object slides over another?

Answer 8

Heat effect - drill into a log can start a fire
Wear effect - worn-out bicycle tyre

Question 9

T or F

Air resistance is a non-contact force that opposite the motion of the object

Answer 9

False

Air resistance is a contact force that opposite the motion of the object

Question 10

What is the relationship between the speed of the object and the air resistance?

Answer 10

The faster the object, the greater the air resistance

Question 11

What is air resistance?

Answer 11

An opposite force acts on a object moving through air

Question 12

Explain why people use different ways to reduce the friction and air resistance

Answer 12

Prevent to slow down and even stop the object
Prevent the object from wear down as it moves against friction and air resistance

Question 13

Give 3 ways how to reduce the friction

Answer 13

Use ball-bearings - change the sliding motion to rolling motion, e.g. wheels on the luggage
Use air cushion - separate the object from the surface with a layer of air, e.g. hovercraft, the puck in the air hockey
Use lubricant oil - separate the object from the surface with lubricant oil, e.g. take off the ring using soap water

Question 14

How to reduce the air resistance?

Answer 14

Streamline the shape of the object, e.g. aeroplane, bicycle helmet

Question 15

Give some examples why friction and air resistance sometimes are essential in our life

Answer 15

Friction between shoes and the ground - walk without slip
Friction between pencil and paper - leaving mark on paper (pencil wear down)
Friction between chopsticks and food - pick up food
Friction between your hand and the lid of a jar - open the jar
Friction between brake pads and the wheel - slow down the wheel
Air resistance acting on the parachute - slow down the fall of skydiver and land safely