1. S I R I S A A C N E WTON
( ) JP

2. JP

3. JP

4. (1686) Philosophiae Naturalis Principia Mathematica
In this work, he proposed three “laws” of motion: JP

5. NEWTON’S FIRST LAW :
“Every body continues in a state of rest or uniform motion in a straight line unless impressed forces
act upon it.” JP

6. “Every body continues in a state of rest or
parked up
NEWTON’S FIRST LAW :
“Every body continues in a state of rest or
uniform motion in a straight line unless
impressed forces act upon it.” JP

7. AAAAAAAH
STATE OF REST
UNLESS ……. ! JP

8. YOU UNDERSTAND WHAT I AM SAYING
NEWTON’s FIRST LAW
… constant velocity, unless ……..
YOU UNDERSTAND WHAT I AM SAYING JP

9. THE PRACTICAL MEASURE OF INERTIA IS
NEWTON’s FIRST LAW INTRODUCES THE IDEA OF INERTIA
THE RELUCTANCE OF A BODY AT REST TO MOVE
(OR OF A MOVING BODY TO CHANGE ITS STATE OF MOTION)
MASS
THE PRACTICAL MEASURE OF INERTIA IS JP

10. The greater the mass of a body, the greater its INERTIA
Make me JP

11. Car stops but inertia carries pendulum forward
CAR SEAT
BELT
locking rod
pivots
seat belt
Car stops but inertia carries pendulum forward
ratchet wheel
Direction of motion JP

12. WHEN FORCES ARE BALANCED
OBJECTS IN MOTION, STAY IN MOTION
[SAME SPEED & DIRECTION]
OBJECTS AT REST, STAY AT REST JP

13. A body is in a state of equilibrium if the forces acting on it are in balance
2 forces balanced
8 N 8N
1200
1200
1200
3 forces balanced JP

14. THERE ARE TWO CONDITIONS FOR A BODY TO BE IN EQUILIBRIUM:
THE SUM OF THE FORCES IN
ANY DIRECTION IS ZERO
THE SUM OF THE MOMENTS
ABOUT ANY POINT IS ZERO JP

15. CAN YOU EXPLAIN WHAT HAPPENS BELOW?JP

16. WHEN FORCES ARE NOT BALANCED
A RESULTANT FORCE CHANGES A BODY’S VELOCITY JP

17. NEWTON’S SECOND LAW :
“THE RATE OF CHANGE OF MOMENTUM OF A BODY IS DIRECTLY PROPORTIONAL TO THE RESULTANT EXTERNAL FORCES ACTING UPON IT, AND TAKES PLACE IN THE DIRECTION OF THAT FORCE” JP

18. A RESULTANT FORCE PRODUCES A CHANGE7
FORCE 7
FORCE 7
FORCE 7
FORCE
A RESULTANT FORCE PRODUCES A CHANGE
IN A BODY’S MOMENTUM
A RESULTANT FORCE AN ACCELERATION JP

19. F = m a JP

20. u n i t s NEWTON’S SECOND LAW F in Newtons m in kilograms
a in metres per second2 JP

21. ACCELERATION IS DIRECTLY PROPORTIONAL TO THE APPLIED FORCE
acceleration / ms-2
force / N
N.B. - STRAIGHT LINE THROUGH THE ORIGIN JP

22. GRAPH OF ACCELERATION VERSUS MASS
acceleration / ms-2
mass / kg
F = m a JP

23. ACCELERATION IS INVERSELY PROPORTIONAL TO MASS OF THE BODY
acceleration / ms-2
N.B. - STRAIGHT LINE THROUGH THE ORIGIN JP

24. NEWTON’S SECOND LAW IS USED IN TWO FORMS
Where F is the RESULTANT FORCE JP

25. JP

26. “ACTION AND REACTION ARE ALWAYS EQUAL AND OPPOSITE”
NEWTON’S THIRD LAW :
“ACTION AND REACTION ARE ALWAYS EQUAL AND OPPOSITE”
“IF A BODY A EXERTS A FORCE ON BODY B, THEN B EXERTS AN EQUAL AND OPPOSITELY DIRECTED FORCE ON A” JP

27. WELL ACTION AND REACTION ARE ALWAYS EQUAL AND OPPOSITE!!
devishly
clever
I’LL PULL HIM
WELL ACTION AND REACTION ARE ALWAYS EQUAL AND OPPOSITE!! JP

28. WELL ACTION AND REACTION ARE ALWAYS EQUAL AND OPPOSITE!!
SO WHY DOES THE GIRL MOVE FASTER? JP

29. NEWTON’S THIRD LAW PAIRS
THEY ARE EQUAL IN MAGNITUDE
THEY ARE OPPOSITE IN DIRECTION
THEY ACT ON DIFFERENT BODIES JP

30. NEWTON’S THIRD LAW PAIRS
SIMILARITIES
DIFFERENCES
The 2 forces act for the same length of time
The 2 forces act on different bodies
The 2 forces are in opposite directions
The 2 forces are the same size
The 2 forces act along the same line
Both forces are of the same type JP

31. THE CLUB EXERTS A FORCE F ON THE BALL
THE BALL EXERTS A N EQUAL AND OPPOSITE FORCE F ON THE CLUB F F JP

32. Drawing Free-Body Diagrams
A free-body diagram singles out a body from its neighbours and shows the forces, including reactive forces acting on it.
Free-body diagrams are used to show the relative magnitude and direction of all forces acting upon an object in a given situation.
The size of an arrow in a free-body diagram is reflective of the magnitude of the force. The direction of the arrow reveals the direction in which the force is acting. Each force arrow in the diagram is labeled to indicate the exact type of force. JP

33. Free body diagram for the ship
Tug assisting a ship
Free body diagram for the ship
Upthrust [buoyancy]
Thrust from engines
SHIP
Pull from tug
weight
Friction JP

34. EXAMPLE 1 - A LIFT ACCELERATING UPWARDS
If g = 10 ms-2, what “g force” does the passenger experience?
The forces experienced by the passenger are her weight, mg and the normal reaction force R.
a = 20 ms-2 R
The resultant upward force which gives her the same acceleration as the lift is R – mg. mg
Apply F = ma
R – mg = ma
Hence the forces she “feels”, R = ma + mg
The “g force” is the ratio of this force to her weight.
JP ©