F2 IS 2nd Term WS03 Answers

2nd Term WS 03 Submission date：_____________ Name：______________________ Class & no.：2 _________(     )

9.3       Force of gravity

i      Words to know:

	English term	Write the words again	Chinese term
1	Force of gravity		重力/引力
2	Pull / Pulling		拉
3	Exert (... on…)		施加 (…於…)
4	Centre		中心
5	Celestial bodies		天體
6	Weight		重量
7	Mass		質量
8	Matter		物質

i      Fill in the blanks:

1      The Earth exerts a pulling force on every object on or around it.

         The force of gravity pulls objects towards the centre of the Earth

2      Other celestial bodies          also exert a force of gravity on objects on or around them.

3       The weight of an object on the Earth is the force of gravity exerted by the Earth on the object.

         It can be different when it is measured on different celestial bodies.

4       The mass of an object is the amount of matters it contains.

         It is the same in all places.

5       The unit of weight is newton while that of mass is kilograms or grams (g).

6       An astronaut is weighing a 2kg block on planet X and the reading is 10N. The mass of the block on planet X

         is 2kg and the mass of the block on the Earth is 2kg . The force of gravity exerted by

         planet X is on the block is 10N. The force of gravity of planet X is smaller (larger / smaller)

         than that of the Earth. The weight of the astronaut on planet X is smaller than his weight on the Earth

i      Skill development – Writing

1.      The Earth exerts a force of gravity on every object on or around it. The force pulls the objects

towards the centre of the Earth.

2.       The Moon exerts a force of gravity on every object on or around it. The force

pulls the objects towards the centre of the Moon.

3.       Mars (火星) exerts a force of gravity on every object on or around it.

The force pulls the objects towards the centre of the Mars.

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F2 IS 2nd Term WS02 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		摩擦力
2	Oppose		相反 / 阻礙
3	Slide / sliding		滑動
4	Air (or water) resistance		空氣 (或水) 的阻力
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      Fill in the blanks:

1      Friction is a force that opposes the sliding motion of objects. It acts along the contacting surfaces of two objects.

2      Air resistance opposes the motion of objects moving through air while

         water resistance opposes the motion of objects moving through water.

3       Explain how friction is reduced in the following examples.

i      Concept checking

Decide whether the following statements are true or false, and try to rewrite the true statements.

1       Friction always causes inconvenience.                                                                            True / False

Friction may cause inconvenience.

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

_____________________________________________________________________________________

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)

___________________________________________________________________________________________

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

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

Friction between a door knob and our hand enables us to open the door. (or other reasonable answers)

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

We sometimes 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.

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

Kinetic energy is changed into heat energy.

F2 IS 2nd Term WS01 Answers

2nd Term WS 01 Submission date：_____________ Name：______________________ Class & no.：2 _________(     )

9.1       Forces

i      Words to know:

	English term	Write the words again	Chinese term
1	Force		力
2	Motion		運動
3	Direction		方向
4	Speed		速度
5	Spring balance		彈簧秤
6	Newton		牛頓
7	Contact force		接觸力
8	Non-contact force		非接觸力

i      Fill in the blanks:

1      A force can:

         start the motion of an object; stop the motion of an object;

         change the direction / speed of motion of an object; and

         change the speed / direction of motion of an object.

2      In a school laboratory, we can use a spring balance to measure forces.

         The unit of force is newton and the symbol is N.

3       Contact forces are forces that act on objects through direct contact.

4       Non-contact forces are forces that act on objects without direct contact.