1. Newton’s Laws of Motion

2. This is true, but does it mean that objects stop by themselves?
Early Thoughts on Motion
From the time of the ancient Greeks to the Medieval age, scientists believed that things tended to stop if left to themselves.
This is true, but does it mean that objects stop by themselves?

3. Galileo investigated this idea with several experiments.
BJU Press Art
Physical Sc. text p. 109

4. Early Thoughts on Motion
Galileo concluded that objects have no natural tendency to stop.
In order for an object to stop, it must be affected by some outside influence.
He called this property inertia.

5. Newton’s Laws of Motion
Newton had clocks that were accurate enough to make time measurements.
He extended Galileo’s studies and formulated his laws of motion.

6. First Law—Inertia Objects at rest remain at rest.
Objects in motion continue in that motion.
Both of these statements change if a net unbalanced external force acts on the object.

7. First Law—Inertia We cannot measure inertia directly.
We measure it indirectly by measuring the mass of an object.

8. First Law—Inertia
If no net force acts on an object, it is in equilibrium.
If any unbalanced force acts on an object, it will change its motion.
The force can be a contact force or a field force or a combination of both.

9. First Law—Inertia Summary:
Inertia is the property of all objects to have an unwilling-ness to change motion.
The more mass an object possesses, the more inertia it has.

10. Second Law—Accelerated Motion
This law states the relationship between force, mass, and acceleration in the form of an equation.
F = ma

11. Second Law—Accelerated Motion
If both sides are divided by m
F = ma m m F
we get .
a = m

12. Second Law—Accelerated Motion
If both sides are divided by a
F = ma a a F
we get .
m = a

13. This is a direct relationship.
Second Law—Accelerated Motion F = m a
increases
increases
If the force increases on an object (constant mass), what happens to the acceleration?
Acceleration increases.
This is a direct relationship.

14. This is why a more powerful engine makes a vehicle go faster.
Second Law—Accelerated Motion F = m a
increases
increases
This is why a more powerful engine makes a vehicle go faster.

15. This is an inverse relationship.
Second Law—Accelerated Motion
increases F = m a
decreases
If the mass of the object increases (constant force), then the acceleration …
decreases.
This is an inverse relationship.

16. Second Law—Accelerated Motion
increases F = m a
decreases
An inverse relationship occurs when one variable going up causes another variable to go down.

17. Second Law—Accelerated Motion
increases F = m a
decreases
This is why a truck with a load accelerates more slowly than when it is empty.

18. Second Law—Accelerated MotionF = m a
If there is no net (unbalanced) force on the object, it does not accelerate.

19. Every action produces an equal and opposite reaction.
Third Law— Action-Reaction
Every action produces an equal and opposite reaction.

20. Third Law— Action-Reaction
When you jump forward out of a boat onto the pier, the boat is pushed backward.

21. Third Law— Action-Reaction
For every force exerted on a system by its surroundings, the system exerts an equal but opposite force on its surroundings.
No force could be exerted if this did not happen.

22. Third Law— Action-Reaction
Even though we call this the “action-reaction” law, motion is not required.

23. Third Law— Action-Reaction
A baseball pushes down on the desktop.
The desktop resists that force with an equal but opposite force.
desk’s force on the ball
BJU Press Art
Physical Sc. text p. 105
ball’s force on the desk

24. Third Law— Action- Reaction
What would happen if an elephant were lowered onto a desk?

25. Third Law— Action-Reaction
What would happen if an elephant were lowered onto a desk?
The desk would collapse because it could not resist with an equal but upward force.

26. Third Law— Action-Reaction
The earth attracts the moon.
The moon attracts the earth with an equal but opposite force.
BJU Press Art
Physical Sc. text p. 113
moon’s force on earth
earth’s force on moon

27. Third Law— Action-Reaction
Rockets utilize this principle. Hot gases exert a force downward and the rocket itself is pushed upward with an equal but opposite force.

28. BJU Press Art
Physical Sc. text p. 113

29. unbalanced large small instantaneous
Newton’s First Law of Motion states that the motion of an object will change when this type of force is applied.
unbalanced
large
small
instantaneous

30. Measuring inertia is really measuring
time.
space.
mass.
distance.

31. What force is required to accelerate an object with a mass of 1,000 kg 2 m/s2?

32. Which Law?

33. Which Law?
2nd Law of Motion

34. Which Law?

35. Which Law?
1st Law of Motion

36. Which Law?

37. Which Law?
3rd Law of Motion

38. Which Law?

39. Which Law?
1st Law of Motion

40. Which Law?

41. Which Law?
2nd Law of Motion

42. Which Law?

43. Which Law?
3rd Law of Motion

44. a contact force that opposes the movement of an object
Friction
a contact force that opposes the movement of an object

45. Friction motion friction
That means the friction vector always points away from the direction of the object’s movement.
BJU Press Art
Physical Sc. text p. 90
motion
friction

46. Friction There are four types of friction: Static – stationary
Kinetic – sliding
Rolling
Fluid

47. Friction There are many factors that affect the amount of friction:
If an object is moving against a surface, there will be friction.
Different amounts of materials create different amounts of friction.

48. Friction
Increasing the force pushing the object against the surface increases the amount of friction.

49. Friction
The friction between stationary objects (static friction) is greater than moving friction.
This means that it takes more force to get something moving than it does to keep it moving.

50. Normal Force This does not mean “usual” force.
The term “normal” in physics means perpendicular (90°) to a surface.

51. Normal Force
When you stand upright, your weight pushes straight down. The earth resists that downward force with an equal and opposite upward force, the normal force.
Of course, this “straight upward” force is perpendicular to the ground.

52. Normal Force
If you are on a sloped surface, like a hill, you are still being attracted straight down to the center of the earth, but it is slanted when compared to the slope of the hill.
The normal force angles so that it remains perpendicular to the ground.

53. Normal Force normal force friction sliding force weight BJU Press art
Physical Sc. text p. 114

54. perpendicular to the roof
A carpenter is standing on the angled roof of a house. What is the direction of the normal force between the carpenter and roof?
straight up
parallel to the roof
straight down
perpendicular to the roof

55. perpendicular to the roof straight down parallel to the roof
A carpenter is standing on the angled roof of a house. What is the direction of the force of the carpenter’s weight?
perpendicular to the roof
straight down
parallel to the roof
straight up