1. Newton’s First Law of motion (牛頓運動第一定律)
Ch.7
Newton’s First Law of motion
(牛頓運動第一定律)

2. 7.1 Experiment 1

4. The card moves away. 4

5. The coin falls on the cup.
The card moves away.
The coin falls on the cup. 5

6. The coin falls on the cup.
The card moves away.
The coin falls on the cup.
The coin tends to stay at rest. 6

7. 7.2 Newton’s First Law
“Every object remains its state of motion if there is no resultant force acting on it.”

8. If no (resultant) force is acting on the object, its state of motion will not be changed.8

9. R W 9

10. If no (resultant) force is acting on the object, a moving object will remains its velocity. The object will move at constant speed along a straight line (i.e. constant velocity/uniform motion). 10

12. The friction is smaller.12

14. friction 14

15. friction
weight 15

16. friction
weight
reaction 16

17. 17

18. resultant force = 0 18

19. resultant force = 0
friction = 60 N 19

20. resultant force = 0
friction = 60 N
reaction = weight = 100 N 20

21. 21

23. T R T f W W 23

24. T R T f W W
resultant force on X = 0
resultant force on Y = 0 24

25. resultant force on X = 0 resultant force on Y = 0 T = Wy = 30 N T R TWx Wy
resultant force on X = 0
resultant force on Y = 0
T = Wy = 30 N 25

27. f = T = 30 N 27

28. 28

29. According to Newton’s First Law, the passenger tends to remain its state of motion, i.e. it is moving with the car. As a result, when the car sudden stops, the passenger will move forward to the windscreen of the car. 29

30. 30

31. The cup tends to remain its state of motion, i. e
The cup tends to remain its state of motion, i.e. remains at rest according to Newton’s First Law. Therefore, when the tablecloth is pulled quickly, the cup remains at rest and does not follow the motion of the tablecloth. 31