1. Motion & Forces

2. Standard
SPS8. Students will determine relationships among force, mass, and motion.
Calculate velocity and acceleration.
b. Apply Newton’s three laws to everyday situations by explaining the following: Inertia, Relationship between force, mass and acceleration, Equal and opposite forces
c. Relate falling objects to gravitational force
d. Explain the difference in mass and weight.

3. What is Motion?
Motion: A change in position of an object compared to a reference point

4. What is a Force?
FORCE = Any push or pull which causes something to move or change its speed or direction

5. What is a Force? Forces can be BALANCED or UNBALANCED
Balanced forces are equal in size and opposite in direction and they don’t change motion.

6. What is a Force?
Unbalanced forces are not equal in size and or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results.

7. What is a Force?
Unbalanced forces are not equal in size and or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results.

8. - The Nature of Force
Combining Forces
The combination of all forces acting on an object is called the net force.

9. What is a Force? Balanced Forces? Unbalanced Forces?
Can you think of examples of forces?
Balanced Forces?
Unbalanced Forces?

10. Types of Forces I. Contact Forces II. Non-Contact Forces
Frictional Force
Normal Force
Applied Force
Spring Force
Air Resistance Force
II. Non-Contact Forces
Gravitational Force
Electrical Force
Magnetic Force

11. Drawing Free-Body Diagrams
Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.

13. What is Gravity? GRAVITY: An attraction force between all masses
Newton’s universal law of gravitation: Every object in the universe exerts a gravitational attraction on all other objects in the universe
The amount of gravitational force depends upon the mass of the objects and the distance between the objects

14. Law of Universal Gravitation

15. - Friction and Gravity
Gravity
Two factors affect the gravitational attraction between objects: mass and distance.

16. What is Gravity? The greater the mass, the greater the force
The greater the distance, the less the force
Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2 near the surface of the Earth

17. Newton's Laws of Motion

18. The tendency of an object to resist any change in its motion
Inertia
A property of matter
The tendency of an object to resist any change in its motion
The greater the mass the greater the inertia
The greater the speed the greater the inertia

19. More Mass More Inertia Less Mass Less Inertia

20. Inertia in Effect 1st Law

21. Newton's Laws of Motion
First Law: An object at rest stays at rest or an object in motion, stays in motion (in the same direction/at the same speed) unless acted upon by an unbalanced force
Also called the law of inertia

23. Momentum: The quantity of motion
A property of moving objects
Calculated by: P = mv
(p = momentum, m = mass, v = velocity)
Law of conservation of momentum: the total amount of momentum of a group of objects does not change unless outside forces act on the objects

24. Momentum = Mass x Velocity
Which has more momentum: a 300lb football player moving at 5m/s or a 200lb quarterback moving at 10m/s?

25. Answer: Momentum of the 300lb player is 300lbs x 5m/s = 1500lb-m/s
Momentum of the quarterback is
200lbs x 10m/s = 2000lb-m/s
The quarterback has a greater momentum!

26. 1st Law

27. Newton's Laws of Motion
Second law: The greater the force applied to an object, the more the object will accelerate. It takes more force to accelerate an object with a lot of mass than to accelerate something with very little mass.
The player in black had more acceleration thus he hit with a greater amount of force

28. Newton's Laws of Motion Second law:
The greater the force, the greater the acceleration
The greater the mass, the greater the force needed for the same acceleration
Calculated by: F = ma
(F = force, m = mass, a = acceleration)

29. Fnet = MA
Net Force = Mass x Acceleration

30. Fnet = MA
Small masses are…
easy to accelerate.

31. Fnet = MA
Which car wins the race assuming drag, friction and Fnet are the same for both?
40g
51g

32. Examples of Newton’s 2nd Law
a) hitting a baseball, the harder the hit, the faster the ball goes
b) accelerating or decelerating a car
c) the positioning of football players - massive players on the line with lighter (faster to accelerate) players in the backfield
d) a loaded versus an unloaded truck

33. Examples of Newton’s 2nd Law
The second law states that unbalanced forces cause objects to accelerate with an acceleration which is directly proportional to the net force and inversely proportional to the mass. This one is telling us that big heavy objects don’t move as fast or as easily as smaller lighter objects. It takes more to slow down a charging bull then to slow down a charging mouse.

34. Newton's Laws of Motion
third law: For every action force, there is an equal and opposite reaction force. (Forces are always paired)

35. Water is pushed and it pushes back and the boat is pushed forward.

36. 3rd Law
There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.

37. Newton’s 3rd Law in Nature
Consider the movement of a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forward, moving the fish through the water.
The size of the force on the water equals the size of the force on the fish; the direction of the force on the water is opposite the direction of the force on the fish.

38. 3rd Law
Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

39. Consider the flying motion of birds. A bird flies by use of its wings
Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. Action-reaction force pairs make it possible for birds to fly.

40. Other examples of Newton’s Third Law
The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).

41. Action/Reaction Forces
Baseball pushes glove leftwards Action
The glove pushes the baseball rightward Reaction

42. 3rd Law
The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases.
The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction.

43. Examples of Newton’s 3rd Law
rockets leaving earth
guns being fired
c) jumping out of a boat onto the dock

44. Weight is a measure of the gravitational force between two objects
The greater the mass the greater the force (weight)
Measured in units called Newtons (N)

45. Free fall - the motion of a falling object when the only force acting on it is gravity

46. Weightlessness – free from the effects of gravity

47. Terminal velocity- gravity will accelerate an object until air resistance (friction) does not allow it to go any faster.
gravity
air resistance

48. Air resistance: The force of air exerted on a falling object
The air pushes up as gravity pulls down
Dependent upon the shape and surface area of the object
When the air resistance equals the force of gravity, terminal velocity is reached
Terminal velocity is the highest velocity that an object will reach as it falls

49. What is Friction?
What are some ways athletes uses friction?

50. What is Friction? Friction = A force that opposes or slows down motion
Caused by the physical contact between moving surfaces
The amount of friction depends upon the kinds of surfaces and the force pressing the surfaces together
Friction changes motion into heat

51. There are four main types of friction:
What is this unbalanced force that acts on an object in motion?
Friction!
There are four main types of friction:
Sliding friction: ice skating
Rolling friction: bowling
Fluid friction (air or liquid): air or water resistance
Static friction: initial friction when moving an object

52. Friction  
the resistance force that occurs when two surfaces travel past each other.
causes physical warping
generates heat

53. Friction  
the resistive force that occurs when two surfaces contact each other.  

54. Sliding friction-the drag force created when the surface of one object slides across the surface of another object.
Sliding Friction Lab
Object
Surface
force (Newstons)

55. Pauline needs to measure the sliding friction of a brick
Pauline needs to measure the sliding friction of a brick. How should she go about doing this?
She should attach a string to the brick and drag the brick so that it gradually speeds up along the surface of a table at a constant speed and read the force in newton’s on the scale.
If you want to measure the weight/mass of the brick hang the brick from a string attached to a spring scale and read the force exerted on the brick due to gravity.

56. Record the Maximum Force (F) (Before the Battery Begins to Move)
Maximum Force F = 110 g

57. Record the Weight (W ) of the Battery
Fw=mass x gravity
580 g

58. N F fs Spring Scale W Surfaces in Contact M1
Experimenting with different materials and contact forces (weights) will yield different values for the coefficient of friction. The implication of this is clear, different materials grip or slide better or worse with respect to each other, and to increase traction on hard surfaces it is best to add weight directly over the driving wheels of a vehicle.

59. Cue Question Check ) What units are used to measure speed?
) What units are used to measure acceleration?
3) What is name of the unit used to measure force in the metric system?

60. Force by Brainpop
) What famous physicist are units of force named after?
) What does velocity measure?
) If Moby has a mass of 50 kg and Tim has a mass of 40 kg, who would require more force to move?

61. Newton’s Laws by Brainpop
) Why does a ball roll across a rug and come to a stop?
) What is a net force?
) Give an example of Newton’s 3rd Law: