1. Aristotle 4th Century Natural Motion Up or down Violent Motion
Newton’s 1st Law
Aristotle
4th Century
Natural Motion
Up or down
Violent Motion
Pushed or pulled

2. Galileo Galilei 1564-1642 Force is a push or pull
Newton’s 1st Law
Galileo Galilei
Force is a push or pull
Friction is the force between materials- caused by irregularities in surface
Inertia
Galileo explains his discoveries to the pope

3. Motion and Forces
Inertia
Inertia (ih NUR shuh) is the tendency of an object to resist any change in its motion.
It will keep moving at the same speed and in the same direction unless an unbalanced force acts on it.

4. Motion and Forces
Inertia
The velocity of the object remains constant unless a force changes it.
If an object is at rest, it tends to remain at rest. Its velocity is zero unless a force makes it move.

5. Motion and Forces
Newton's Laws of Motion
The British scientist Sir Isaac Newton (1642–1727) was able to state rules that describe the effects of forces on the motion of objects.
These rules are known as Newton's law's of motion.

6. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
Newton's first law of motion is that an object stays at rest or stays at a constant velocity unless acted upon by a net (unbalanced) force
This law is sometimes called the law of inertia.
( you might know this as an object at rest stays at rest, an object in motion stays in motion unless acted upon by an unbalanced force)

7. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
What happens to the speed of a sliding object on ice?
Without friction speed doesn’t change…. You just keep going!

8. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
What happens to the speed of a sliding object if I put the same object on carpet?
With friction speed changes dramatically. You slow down, not because it is “natural” but because there is a force slowing you down

9. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
Where did we see Newton’s 1st Law with projectiles?
Horizontal !
No horizontal net force means motion is constant
x=vt

10. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
Coin in car
Also at your feet because it maintains the initial horizontal velocity while in the air

11. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
Does this law pertain to moving objects, objects at rest or both?

12. Forces Push or pull Can be At-a-distance Gravity/charges Contact
Motion and Forces
Forces
Push or pull
Can be
At-a-distance
Gravity/charges
Contact
friction

13. the forces do not cancel each other
Motion and Forces
Unbalanced Forces
the forces do not cancel each other

14. Motion and Forces
Unbalanced Forces
The students are pushing on the box in the same direction.
These forces are combined, or added together, because they are exerted on the box in the same direction.

15. Motion and Forces
Balanced Forces
The net force on the box is zero because the two forces cancel each other.
Forces on an object that are equal in size and opposite in direction are called balanced forces.

16. Possible Motions What are the possible motions for an object with
Motion and Forces
Possible Motions
What are the possible motions for an object with
Unbalanced forces Balanced Forces

17. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
How much force does it require to keep a cannonball going once launched into outer space?
None!

18. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
Demonstrations
Astronauts
Tablecloth
Eggs
Seatbelts

19. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
Table cloth
Static (stuck) friction = net force when moving slow
Kinetic (moving/sliding) friction = net force when moving fast
Kinetic is much weaker than static friction

20. Newton's First Law of Motion
Motion and Forces
Newton's First Law of Motion
stuck together
strong
walking
Sliding past
weak
Sliding into home base

21. Newton’s Second Law
If you push horizontally on your book with a force of 1 N to make the book slide with a constant velocity, how much is the force of friction on the book?
1 N ?
1 N

22. Newton’s Second Law
a freebody diagram shows the forces acting on an object (at the center of mass) using arrows

23. Newton’s Second Law
Newton’s second law of motion states that a unbalanced (net force) results in an acceleration

24. Unbalanced Forces
net force is the combination of forces acting on an object (unbalanced force)
FNet Newtons
When two students are pushing with unequal forces in opposite directions, a net force occurs in the direction of the larger force.

25. Mass m kg NOT Volume (space) Force IS
Property of objects that resists a change in motion (inertia)
How much “stuff” or how many atoms
Measured in kilograms
m kg

26. Acceleration is how quickly velocity changes
Acceleration is how quickly velocity changes. When the velocity of an object changes, the object is accelerating.
Symbol: a
Unit: m/s2

27. Newton’s Second Law
Fnet= ma
Fnet
m a
Newton’s second law of motion states that a net force (unbalanced force) results in an acceleration

28. Net Forces
Large mass vs Small mass

29. Math Practice

30. Gravity
What is gravity?
Gravity is an attractive force between any two objects that depends on the masses of the objects and the distance between them.

31. Gravity
What is gravity?

32. Weight The gravitational force exerted on an object
Gravity
Weight
The gravitational force exerted on an object
Arrow that points downward on every freebody diagram
Symbol: W
Unit : Newton

33. Mass IS Inertia Tendency of an object to resist a change in motion
Motion and Forces
Mass IS
Inertia
Tendency of an object to resist a change in motion
Symbol: m
Unit: kg

34. Earth’s Gravitational Acceleration
Gravity
Earth’s Gravitational Acceleration
Close to Earth’s surface, the acceleration of a falling object in free fall is about 9.8 m/s2.
This acceleration is given the symbol g and is sometimes called the acceleration of gravity.

35. Gravity
Weight
Because the weight of an object on Earth is equal to the force of Earth’s gravity on the object, weight can be calculated from this equation: W
W= mg
m g

36. Gravity
Weight and Mass
The table shows how various weights on Earth would be different on the Moon and some of the planets.

37. Gravity
Centripetal Force
An unbalanced force that cause a change in direction is a centripetal force.

38. Centripetal Force and Traction
Gravity
Centripetal Force and Traction
Anything that moves in a circle is doing so because a centripetal force is accelerating it toward the center.

39. Centripetal Force and Traction
Gravity
Centripetal Force and Traction
This centripetal force is the frictional force between the tires and the road surface.
This centripetal force is the sides of the washer

40. The Third Law of Motion
Newton’s Third Law
Newton’s third law of motion describes action-reaction pairs this way. When one object exerts a force on a second object, the second one exerts a force on the first that is equal in strength and opposite in direction.
TWO OBJECTS!!!

41. The Third Law of Motion
Action and Reaction
When a force is applied in nature, a reaction force occurs at the same time.
When you jump on a trampoline, for example, you exert a downward force on the trampoline.
Simultaneously, the trampoline exerts an equal force upward, sending you high into the air.

42. Action and Reaction Forces Don’t Cancel
The Third Law of Motion
Action and Reaction Forces Don’t Cancel
According to the third law of motion, action and reaction forces act on different objects.
Thus, even though the forces are equal, they are not balanced because they act on different objects.

43. Action and Reaction Forces Don’t Cancel
The Third Law of Motion
Action and Reaction Forces Don’t Cancel
For example, a swimmer “acts” on the water, the “reaction” of the water pushes the swimmer forward.
Thus, a net force, or unbalanced force, acts on the swimmer so a change in his or her motion occurs.

44. The Third Law of Motion
Rocket Propulsion
In a rocket engine, burning fuel produces hot gases. The rocket engine exerts a force on these gases and causes them to escape out the back of the rocket.
By Newton’s third law, the gases exert a force on the rocket and push it forward.

45. Force Pressure Area
Pressure is a force that is over an area of contact P
Pascals or N/m2

46. Force Pressure Area

47. Force Pressure Area F
Pressure = Force/ Area
P A