1. Forces
FORCEMAN

2. Goals
Construct an explanation based on experimental evidence to support the claims presented in Newton’s three laws of motion.
Explain the difference in mass and weight.
Relate falling objects to gravitational force
Analyze and interpret data to identify the relationship between mass and gravitational force for falling objects.
Apply Newton’s three laws to everyday situations by explaining the following:
-Inertia
-Relationship between force, mass and acceleration Equal and opposite forces

3. What causes things to move?
What is a force?
A push or a pull that one body exerts on another.

4. Balanced

5. Question: Can there be balanced forces on a object and the object still have motion?

6. The Body will Accelerate
Unbalanced
If the forces acting on a body are "unbalanced" this means that there is a "net" or "resultant" force.
The object will do one of the following:
Speed Up
Slow Down
Change the Direction of its Motion
In other words….
The Body will Accelerate

8. Questions: How do we measure force?
Newtons
SI unit of force is the Newton (N).
Defined as the amount of force that when acting on a 1 kg object produces an acceleration of 1m/s2.
Therefore, 1N = 1 kg • m s2

9. What will happen? Abruptly stopping a cart with a suitcase on top….
You set your coffee cup on the dash and then make a sharp left turn…..
You throw a tennis ball in outer space.

10. Newton’s First Law

11. Newton’s First Law

12. Newton’s First Law ?What do you mean by “Net Force”?
An object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force.
?What do you mean by “Net Force”?
Net means: Final Sum, so net external force is the sum of all the forces acting on the object.

13. Newton’s First Law
Newton’s First Law is also called the Law of Inertia.
Inertia is the tendency of an object to resist any change in its motion.
Question: Does an object at rest still have inertia?

14. Why does the ladder continue to move?
Inertia!

15. Why does the person continue to move?
Inertia!
Clip

16. Lab Activity
Question: How will the different balls affect the distance the block moves? Be able to explain your answer…

17. Newton’s Second Law F=ma
The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the object’s mass.
F=ma
Clip

18. Newton's 2nd Law of Motion

20. Force = mass x acceleration
Newton's 2nd Law of Motion:
Force = mass x acceleration
F = m x a
Mass is in kg
Acceleration is in m/s2
Force is in kg x m/ s2 (or N)
Let’s do a sample problem…next slide 

21. Force Problems:
What force is needed to give an object with a mass of 25.0 kg an acceleration of 15.0 m/s2 ?
Formula
F = ma
Given:
Unknown:
m = 25.0 kg
a = 15.0 m/sec²
F = ?
F = (25 kg)(15 m/sec²)
F = 375 kg•m/sec² = 375 N

22. Newton’s Third Law of Motion
…to every action force there is an equal and opposite reaction force

23. Newton’s Third Law
"Every action has an equal and opposite reaction."

24. Action-Reaction forces act on different objects

26. Hockey Video Clip

27. Newton’s 3 laws

28. Forces that oppose motion

29. Friction

30. Forces that oppose motion
-Friction is a force that opposes motion between two surfaces that are touching each other.
Friction Song 1
Friction Song 2
Acts in the opposite direction of the motion

31. -Air resistance is the force air exerts on a moving object
Forces that oppose motion
-Air resistance is the force air exerts on a moving object

32. Friction What Causes Friction?
Microscopic, electrostatic interactions between contacting surfaces
Friction

33. 3 types of Friction
Static Friction
Sliding Friction
Rolling Friction

34. Types of Friction Types of friction:
1. Static – force required to overcome inertia of a stationary object

35. Static friction- occurs between the surfaces of 2 objects that touch but do not move against each other. Static friction must be overcome for one of the objects to move.

36. Static Friction (FS)

37. Not enough static friction

38. Types of Friction (cont’.)
2. Sliding – force required to keep an object sliding at a constant speed
3. Rolling – force required to keep an object rolling at a constant speed
To decrease friction, surfaces can be lubricated with a liquid such as oil.

40. Friction Song

41. FRICTION LAB

42. CLIP
The amount of force required to overcome static friction is always greater than the force required to overcome sliding or rolling friction.

43. GRAVITY!! 1- Masses (greater mass means more gravity)
The force of gravity is an attractive force between objects.
The amount of GRAVITATIONAL FORCE between objects depends upon their:
1- Masses (greater mass means more gravity)
2- Distance apart (greater distance means
less gravity)
*All objects fall toward the earth at the same rate of acceleration, regardless of their masses!

44. Calculating the Gravitational Force

46. Weightlessness
Gravity in
Space
Moon
Moon Hammer & Feather

47. Free fall and Terminal Velocity
The opposing force of air resistance increases with speed.
Objects accelerate towards the Earth until the force of gravity is cancelled or balanced by this air resistance.
This is the highest speed an object can reach.
Different objects have different terminal velocities.

48. Practice Problems

49. Weight is measured in Newtons (N).
Weight is the force of gravity between the earth and a body on its surface.
Weight ≠ mass!
Weight is measured in Newtons (N).
BECAUSE IT’S A FORCE!

50. Could your weight change by simply going to the top of a mountain?

51. Weight W = (g)(m) Ex. Mass = 100kg Acc.= 9.81 m/s2 Weight = 981 N
When the mass of an object and the acceleration due to gravity are known, the weight of an object can be calculated.
W = (g)(m)
Ex. Mass = 100kg Acc.= 9.81 m/s2
Weight = 981 N

52. Example Problem What is your weight if your mass 4.52 kilograms?
Given: Unknown:
m = 4.52 kg W = ?
g = a = 9.8 m/sec²
Formula: W = mg
W = (4.52kg)(9.8 m/sec²)
W = kg•m/sec² = N

54. Projectile Motion
Projectiles follow a curved path because of the Earth’s gravitational pull.
They have 2 types of motion that are independent of each other:
1. Horizontal motion
2. Vertical motion

55. Projectile Motion Which will hit the ground first?
A ball that is dropped straight down or a ball that is “shot” out horizontally?
* An object launched horizontally will land on the ground at the same time as an object simply dropped from the same height!!!!

56. Another Example of Projectile Motion

57. only centripetal is the real force
Circular Motion
Roller Coaster Clip
An object moving in a circular motion at the same speed is accelerating toward the center because its direction is constantly changing.
Centripetal acceleration is acceleration toward the center of a curved path.
'Centripetal' comes from the Latin word for 'center seeking'
Centrifugal 'force' is really a function of the inertia of the object being pushed into a circle. It is not really a force at all, it is simply the tendency of an object to go in a straight line.
only centripetal is the real force

58. Circular Motion cont.’
Centripetal force is the force that causes a moving object to move in a curved path
Without a centripetal force, an object in motion continues along a straight-line path.
With a centripetal force, an object in motion will be accelerated and change its direction.

60. Amusement Park Forces

61. Review of Newton’s 3 laws