1. Review for Quiz Tuesday
What is formula for speed?
Speed = distance/time
What must be included for velocity?
Direction
Define acceleration.
Rate of change of an objects speed
What is the formula for acceleration?
A = (final speed – initial speed) / time

2. Distance Vs Time Graph

4. Motion What causes objects to move?

5. Forces A push or pull on an object Measured in Newtons (N)
Causes movement
Stops movement
Determine the amount of movement
Measured in Newtons (N)
Instrument – Spring Scale

6. Are these forces balanced?

7. What affect do balanced/unbalanced forces have on motion?
Balanced: No change in velocity
Therefore constant speed or no motion.
Unbalanced: Always cause a change in motion in the direction of the net force.
(A net force is the sum of all the forces)

8. Newton’s 1st Law of Motion
an object in motion will stay in motion at the same velocity unless a net force acts on it!
an object at rest will remain at rest unless a net force acts on it!
(- the law of Inertia)

9. a.k.a. Law of Inertia Inertia = mass
Inertia: the property of an object (matter) that resists any change in velocity
To make an object move (or stop) you must overcome its inertia
What has more inertia
Bowling ball or a ping-pong ball?
Volkswagen beetle or a garbage truck?
Inertia = mass

10. Formula Inertia Equation (the easiest one this year!)
Inertia = mass (unit = kg)

11. Example What is newtons’ first law of motion?
How does this demonstrate it?

12. Friction A force that opposes motion Causes objects to slow down
Direction of the force is opposite the motion
The pushing force needs to be greater than the frictional force acting on the object for it to begin to move.

13. Newton’s 2nd Law
the acceleration on an object increases as the net force acting on the object increases
acceleration is in the direction of the force

14. F = MA
The force exerted on the object is equal to the objects mass x the acceleration.
You can also solve for Mass or acceleration.
The unit for force is the NEWTON (N)

15. Practice Problems A 20 kg object was accelerated at a rate of
6 m/s². What force was applied to it?
. F = ma F = (20)(6) F = 120 N

16. A force on an object accelerated it a rate of 7. 5 m/s²
A force on an object accelerated it a rate of 7.5 m/s². The object had a mass of 50 kg. What was the measure of the force?
F = ma F = (50)(7.5) F = 375 N

17. A force of 150 N was applied to a 10 kg object
A force of 150 N was applied to a 10 kg object. What was the acceleration produced?
. a = F a = 150 a = 15 m/s² m

18. An object was accelerated at rate of 35 m/s² from a force of 700 N
An object was accelerated at rate of 35 m/s² from a force of 700 N. What would the mass of the object have been?
. m = F m = 700 m = 20 kg a

19. Newton’s 3rd Law
For every action there is an equal and opposite reaction (for forces)
Action-Reaction Pairs of Forces
Action- one object exerts a force on a second object
Reaction- the second object exerts an equal but opposite force on the first

20. In the top picture (below), Kent Budgett is pulling upon a rope which is attached to a wall. In the bottom picture, Kent is pulling upon a rope which is attached to an elephant. In each case, the force scale reads 500 Newtons. Kent is pulling ...
a. with more force when the rope is attached to the wall.
b. with more force when the rope is attached to the elephant.
c. the same force in each case.

21. A fish uses its fins to push water backwards.
In turn, the water reacts by pushing the fish forwards, propelling the fish through the water.

22. For years, space travel was believed to be impossible because there was nothing which rockets could push off of in space in order to provide the propulsion necessary to accelerate. This inability of a rocket to provide propulsion is because ...
a. ... space is void of air so the rockets have nothing to push off of.
b. ... gravity is absent in space.
c. ... space is void of air and so there is no air resistance in space.
d. ... nonsense! Rockets do accelerate in space and have been able to do so for a long time.

23. DO NOW What is force that opposed motion? Friction
How do think mass affects the force of friction?
How do you think the surface the object is on affects friction?
How do you think surface area affects friction?

24. Forces & Motion Lab
1. What do you think will happen with the required force to move the block when mass is added to the block?
2. What do you think will happen with the required force to move the block when the surface that the block is being moved on is changed?
3. What do you think will happen with the required force to move the block when the surface area being dragged on a surface is changed?

25. Conclusions
According to the data what affect did adding mass have on the force?
What affect did changing the surface have on the force?
What affect did reducing the surface area have on the force?

26. Surface Area
If you have two heavy objects of the same mass, where one is half as long and twice as high as the other one, they still experience the same frictional force when you drag them over the ground.
This is because if the area of contact doubles, you may think that you should get twice as much friction. But when you double the length of an object, you halve the force on each square centimeter, because less weight is above it to push down.

27. 4 Types of Friction
Static Friction- Acts on objects when they are at rest. Prevents the car from moving

28. Sliding Friction When two solid surfaces slide across each other.
Makes objects slow down and stop

29. Rolling Friction When an object rolls across a surface.
Sliding friction between two very smooth surfaces like wheels or a ball rolling along the floor.

30. Fluid Friction
Fluids are liquids or gases that flow. Fluid friction occurs when a solid object moves through a fluid.

31. How can friction be reduced?
Oil
Ball bearings
Ice

32. Can Friction be beneficial?
YES!
Walking
Writing

33. DO NOW What is the difference between mass and weight?
Mass is amount of matter, weight is a measure of gravity.
What is acceleration due to gravity?
9.8 m/s/s

34. Gravity A force of attraction between any two objects with mass
Controlled by mass and distance

35. Gravitational Force Attraction between objects Depends on: Mass
Greater the mass = Greater the gravitational force
Distance
Greater the distance = Smaller the gravitational force
Less Gravitational Pull
Greater Gravitational Pull
Greater Gravitational Pull
Less Gravitational Pull

36. Less pull of gravity = Greater Jump Earth is 6x larger than the moon Moon Gravity = 1/6 of the Earth Gravity
Not drawn to scale

37. What is the difference between mass and weight?
Mass: how much matter an object is made of.
Weight- measure of the force of the (Earth’s) gravity on an object
Example
Earth  weight = 180 lbs.
Moon  weight = 180lbs. = 30 lbs

38.
Friction curling video

39. Do Now What is Newton’s first law?
An object in motion will stay in motion unless a net force acts on it.
What is a net force?
The force that is left after they are added together.
What force opposes motion?
Friction

40. Acceleration due to Gravity
On Earth = 9.8 m/s²
Everywhere on Earth the force of gravity is the same so acceleration of a falling object is a constant number.
Although, this would only be constant in a vacuum. (an area with no atmosphere)

41. What slows down a falling object?
Air!
Air Resistance: the force of air opposite the motion of an object in an atmosphere
(fluid friction)
-force is controlled by the shape of the object (aerodynamics)
-force increases as the objects speed increases

42. Will the object always accelerate?
No, eventually the force of air resistance equals the force of gravity.

43. Terminal Velocity -forces become balanced -speed becomes constant
Terminal Velocity- maximum velocity reached by a falling object in an atmosphere
-forces become balanced
-speed becomes constant
-the object is still falling!

44. Why does the elephant hit the ground first?

47. Conclusion
Will an object always accelerate towards the ground at a rate of 9.8 m/s²?
What force causes objects to slow down as they fall?
What is the maximum velocity of a falling object called?

48. DO NOW What is Newton’s second law?
The acceleration on an object increases as the net force acting on the object increases
What is Newton’s third law?
For every action there is an equal and opposite reaction
Which law is a tug-of-war an example of?
Newton’s third law

49. Newton’s 2nd Law Continued
Momentum is a quantity representing the motion of a body. It is directly proportional to both mass and speed.
Momentum = mass x velocity
p = mv (p = momentum)
Unit = kg·m/s

50. Equivalent Momenta
Car: m = 1800 kg; v = 80 m /s p = 1.44 ·105 kg · m /s
Bus: m = 9000 kg; v = 16 m /s p = 1.44 ·105 kg · m /s
Train: m = 3.6 ·104 kg; v = 4 m /s p = 1.44 ·105 kg · m /s

51. Law of Conservation of Momentum
For a collision occurring between object 1 and object 2, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision.
The momentum lost by object 1 is equal to the momentum gained by object 2.

53. Solve Using Momentum Formula
How much momentum does a 25 kg mass moving at 25 m/s have?
P = mv P = (25)(25) = 625 kg m/s
How much momentum does a stationary 5500 kg mass have?
0, it’s not moving so V is 0

54. a: +40 (add the momentum of the bat and the ball)
c: +40 (the total momentum is the same after as it is before the collision)
b: 30 (the bat must have 30 units of momentum in order for the total to be +40)

55. Practice
A baseball player holds a bat loosely and bunts a ball. Express your understanding of momentum conservation by filling in the tables below.

56. A Tomahawk cruise missile is launched from the barrel of a mobile missile launcher. Neglect friction. Express your understanding of momentum conservation by filling in the tables below.

57. a: 0 (add the momentum of the missile and the launcher)
c: 0 (the total momentum is the same after as it is before the collision)
b: (the launcher must have units of momentum in order for the total to be 0)

58. Activity 1. Put 5 steel balls roughly in the center side by side.
2. Move one ball to the edge of the track and roll it down the track to the other four balls that are side by side.
3. Observe and record what happens.
4. Repeat this process by rolling 2,3 and 4 balls at once down the track side by side.