Ch9 Textbook Exercise

Activity 9.1                                                                                                                              p.4

1.          stopped

2.          starts

3.          faster

4.          direction

Experiment 9.1                                                                                                                    p.6-7

Part A

(a)    extends

(b)    force

Part B

2.     (Answer depends on the type of rubber band used.)

3.     (Answers depend on the types of rubber bands used.)

        The force required to stretch different types of rubber band by 3 cm may be different.

Checkpoint 9.1                                                                                                                       p.9

1.      The force of the rolling bowling ball starts the motion of the pins.

2.     

 

                       

3.    (a)    spring balance / newton balance
(b)    newton
(c)    N

4.      (a)    C
(b)    N
(c)    N
(d)   C

Activity 9.2A                                                                                                                         p.11

Experiment 9.2A                                                                                                                  p.12

3.     (Answer depends on the weight used and the paper surface.)

4.     (Answers depend on the weight used and the surfaces.)

Experiment 9.2B                                                                                                             p.13-14

1.     It moves and then stops.

2.     (a)    The puck moves for a longer distance before it stops.

        (b)    Friction is reduced when air is present between the puck and the bench.

Experiment 9.2C                                                                                                                  p.16

Part A

1.     It moves and then stops.

2.     (a)    The puck moves for a longer distance before it stops.

        (b)    The bamboo sticks roll. This reduces the friction between the puck and the bench.

Part B

1.     The weight spins for a short time and then stops.

3.     (a)    The weight spins for a longer time.

        (b)    The marbles roll. This reduces the friction between the weight and the lid.

Activity 9.2B                                                                                                                         p.20

1.       (a)    There are bulges on the material wrapping the bicycle handle, which prevents slipping.

(b)       The grooves on the tyres increase friction and prevent the car from skidding.

(c)        The rough surfaces on the gloves increase friction and prevent the ball from slipping away.

(d)       Edges of stairs are covered with a plastic lining, which prevents slipping.

2.     · 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.

        (any two or other reasonable answers)

Checkpoint 9.2                                                                                                                     p.21

1.     Using a lubricant, using ball bearings (or other reasonable answers)

2.     · 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.     (a)    increased

(b)    reduced

4.     · Friction is reduced because there is a layer of air between the train and the rails.

        · Air resistance is reduced because the train has a streamlined shape.

        (or other reasonable answers)

Experiment 9.3                                                                                                                     p.24

Object	Weight (N)
wooden block (with a hook)	(Answer depends on the wooden block used)
200 g metal weight (with a hook)	about 2 N
pencil box and a rubber band	(Answer depends on the pencil box and rubber band used)

Checkpoint 9.3                                                                                                                     p.25

1.     (a)    force of gravity of the Earth

        (b)    the Earth’s centre

        (c)    force of gravity of Mars

        (d)   Mars’ centre

E 2.     (a)    matter

            (b)    mass

Experiment 9.4A                                                                                                             p.28-29

Part A

2.     Both students A and B move backwards. They move away from each other.

3.     Both students A and B move backwards. They move away from each other.

Part B

The student moves backwards.

Experiment 9.4B                                                                                                             p.30-31

3.     It moves quickly along the string.

4.     When the clip is removed, air is ejected from the balloon. The ejected air exerts a force on the             balloon, pushing it in the opposite direction.

Experiment 9.4C (Demonstration)                                                                                     p.32

3.     (a)    The water is ejected downwards.

        (b)    It moves upwards.

Checkpoint 9.4                                                                                                                     p.38

1.          C