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

2. 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)

3. Motion What causes objects to move?

4. 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

5. Are these forces balanced?

6. 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.
Acceleration

7. 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)

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

9. a.k.a. Law of Inertia
Inertia: the property of an object (matter) that resists any change in velocity
- to make an object move (or stop) you must overcome it’s inertia

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

11. Do now What has more inertia Bowling ball or a ping-pong ball?
Volkswagen beetle or a garbage truck?
State Newton’s First Law

12. What are the outside forces that act on the object?

13. 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.

14. 3 Types of Friction
Static Friction- tries to prevent an object from moving
Sliding Friction- slows down an object sliding on a surface
Rolling Friction- needed to make a wheel turn

15. Can Friction be beneficial?
YES!
Walking
Writing

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

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

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

19. 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

20. 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

21. 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)

22. Do Now What are the forces that slow down or speed up motion? Friction
Gravity
Air resistance

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

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

25. 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!

26. Why does the elephant hit the ground first?

28. 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

29. f = m*a
The force exerted on the object is equal to the objects mass times the acceleration.
You can also solve for mass or acceleration.
The unit for force is the NEWTON (N)

30. 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

31. 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

32. 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

33. 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

34. Newton’s 3rd Law
to 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

35. Consider a fish in the water

36. 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.

37. In the top picture (below), Kent Budgett is pulling upon a rope which is attached to a wall. In the bottom picture, the 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.