F2 IS 2nd Term WS02 9.2 Answers

2nd Term WS 02 Submission date：_____________ Name：______________________ Class & no.：2 _________(     )

9.2       Friction

i    Words to know:

	English term	Write the words again	Chinese term
1	Friction		磨擦力
2	Oppose		相反 / 對抗
3	Slide / sliding		滑動
4	Air (or water) resistance		空氣 (或水) 阻力
5	Air cushion		氣墊
6	Lubricant		潤滑劑
7	Rollers		滾子
8	Ball bearings		滾珠軸承
9	Streamlined shapes		流線型

i     Concept checking: Decide whether the following statements are true or false, and try to rewrite the true statements.

1      Friction only causes inconvenience.                                                                               True / False

Friction sometimes causes inconvenience.

2      Oil reduces friction by separating two contacting surfaces.                                         True / False

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i    Multiple choice: Circle the letter of the best answer for each question.

1.      Which of the following properties of an object is NOT affected by a force?

1. Shape
2. Weight
3. Mass
4. Direction of motion

2.      Which of the following is/are NOT example(s) of reducing friction?

(I)                 The air cushion of a hovercraft

(II)               The streamlined shape of a racing car

(III)             Covering a wet floor with a piece of thick cloth

1. (I) only
2. (III) only
3. (I) and (II) only
4. (II) and (III) only

i    Short question

1.      Suggest TWO ways to reduce friction between two contacting surfaces.

Using a air cushion / a lubricant / ball bearings (any TWO)

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2.      Suggest TWO examples from daily life where friction is useful to us.

Friction between our shoes and the ground enables us to walk or run.

Friction between a door knob and our hand enables us to open the door.

(OR other reasonable answers)

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3.      Suggest TWO examples in daily life where friction is increased.

We use a towel to increase friction when trying to open the lid of a bottle.

/ Hiking boots have deep grooves on the sole to increase friction and prevent slipping.

/ The plastic non-slip grip on a ball-pen prevents slipping and makes writing easier.

/ Using a folk or chopstick to pick up food.

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4.      What energy change is involved when two objects are continuously to rubbed against each other?

Kinetic energy is changed into heat energy.