1. Motion
Chapter 11

2. Standards Students will:
SPS8. Determine the relationship between force, mass and motion
SPS8a Calculate velocity and acceleration
SPS8c Relate falling objects to gravitational force
SPS8d Explain difference in mass and weight

3. Observing Motion
Motion- change in position in relation to a reference point.

4. Measuring Motion: Distance
Distance- how far an object moves on a path
Displacement- how far between starting and ending points on a path

5. Measuring Motion: Speed
rate of motion
distance traveled per unit time
speed = distance
time

6. Measuring Motion: Speed (cont’d)
Instantaneous Speed
speed at a given instant
Average Speed-
= total distance
total time

7. Measuring Motion: Velocity
speed in a given direction
can change even when the speed is constant!

8. Calculating Velocity: Distance/Speed/Time Triangle

9. Graphing Speed/Velocity
X axis- usually independent variable (time)
Y axis- usually dependent variable (distance)
Slope of straight line= vertical change
horizontal change

10. Graphing (cont’d) slope = velocity steeper slope = faster velocity
straight line = constant velocity
flat line = 0 velocity
(no motion)

11. Calculating Slope Choose two points on graph to calculate slope.
Distance Vs Time 16
Choose two points on graph to calculate slope.
Calculate the vertical and horizontal change.
Divide the vertical change by the horizontal change. 14 . 12 10
Distance (m) 8 . 6 4 2 1 2 3 4 5
Time (s)

12. Calculating Slope(cont’d)
Distance Vs Time 16
1. point 1: d= 6m t= 1s point 2: d= 12m t= 4s 2. vert ∆- 12m-6m= 6m horiz ∆- 4s-1s= 3s 3. slope= 6m = 2m/s 3s 14 . 12 10
Vertical
change
Distance (m) 8 . 6
Horizontal
Change 4 2 1 2 3 4 5
Time (s)

13. Practice Problem A B Who started out faster? A (steeper slope)
Who had a constant speed? A
Describe B from min.
B stopped moving
Find their average speeds.
A = (2400m) ÷ (30min) A = 80 m/min
B = (1200m) ÷ (30min) B = 40 m/min A B

14. Measuring Motion: Acceleration
the rate of change of velocity
change in speed or direction
Centripetal acceleration
circular motion (even if speed is constant, direction is always changing)
ex. Moon accelerates around Earth

15. Measuring Motion: Acceleration
Positive acceleration
-“speeding up”
Negative acceleration
-“slowing down”

16. Calculating Acceleration
a= vf – vi t
a= ∆ v
a- acceleration
vf- final velocity
vi- initial velocity
t- time

17. Calculating Acceleration (cont’d)
List given, then unknown values.
Write equation for acceleration.
Insert known values into equation and solve.
Vf-Vi
a t t

18. Practice Problem 1
A flowerpot falls off a second-story windowsill. The flowerpot starts from rest and hits Mr. Mertz 1.5s later with a velocity of 14.7m/s. Find the average acceleration of the flowerpot. Given: Remember: Solve: t= 1.5s a= vf – vi a= 14.7m/s-0m/s Vi= 0m/s t 1.5s Vf= 14.7m/s a= 14.7m/s a= ? 1.5s a= 9.8m/s2

19. Practice Problem 2
Joseph’s car accelerates at an average rate of 2.6m/s2. How long will it take his car to speed up from 24.6m/s to 26.8m/s2? Given: Remember: Solve: a= 2.6m/s2 t= (vf-vi) ÷ a vf= 26.8m/s2 vf-vi t= 26.8m/s2-24.6m/s2 Vi= 24.6m/s2 a t 2.6m/s2 t= ? t= 2.2m/s 2.6m/s2 t= 0.85s

20. Practice Problem 3
A cyclist travels at a constant velocity of 4.5m/s westward and then speeds up with a steady acceleration of 2.3m/s2. Calculate the cyclist’s speed after accelerating for 5.0s. Given: Remember: Solve: vi= 4.5m/s vf= vi + a x t vf= ? vf-vi vf= 4.5m/s + (2.3m/s2 x 5.0s) a= 2.3m/s2 a t vf= 4.5m/s m/s t= 5.0s vf= 16m/s

21. Graphing Acceleration
Distance/Time
On Distance-Time
graph:
Acceleration is shown as a curved line

22. Graphing Acceleration
Speed/Time
On a Speed-Time graph:
Slope of straight line= acceleration
Positive slope- speeding up
Negative slope- slowing down
Flat line- constant velocity
(no acceleration)

23. Newton’s Laws of Motion
2nd Law of Motion:
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
Force = mass x acceleration or or
F= ma

24. Force
Force- push or pull that one body exerts on another

25. Fundamental Forces 4 types: 1. gravity 2. electromagnetic
3. weak nuclear
4. strong nuclear
Vary in strength
Act through contact or at a distance

26. Forces Force Pairs: forces moving in opposite directions
Balanced forces: do not
move; push equally on each other
Unbalanced forces:
acceleration (movement) in the direction of larger force

27. Force Pair Examples

28. Friction Friction: force that opposes motion between 2 surfaces
Static Friction: nonmoving surfaces
Kinetic Friction: moving surfaces- sliding or rolling
(sliding friction is greater than rolling friction)

29. Friction Facts Necessary for all motion
Rougher surfaces create greater friction
Greater mass creates greater friction
Lubricants reduce friction

30. Newton’s First and Second Laws
Chapter 12

31. Newton’s Laws of Motion
1st Law of Motion: Law of Inertia
An object at rest will remain at rest;
An object in motion will continue moving at a constant velocity unless acted upon by a net force.

32. Inertia Objects move only when net force is applied.
Objects maintain state of motion.
Inertia is related to mass.
(small mass can be accelerated by small force
large mass can be accelerated by large force)

33. Newton’s Laws of Motion
2nd Law of Motion:
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
Force = mass x acceleration or or
F= ma

34. Newton’s Second Law For equal forces, large masses accelerate less
Force is measured in newtons (N)
1N= 1kg x 1m/s2 F m a

35. Practice Problem 1
Zoo keepers lift a stretcher that holds a sedate lion. The lion’s mass is 175 kg and the upward acceleration of the lion and stretcher is 0.657m/s2. What force is needed to produce acceleration of the lion and stretcher? Given: Remember: Solve: m= 175 kg F = m x a a= 0.657m/s2 F = 175 kg x 0.657m/s2 F= ? m a F = N F F

36. Practice Problem 2
A baseball accelerates downward at 9.8 m/s2. If
gravity is the only force acting on the baseball and is
1.4N, what is the baseball’s mass?
Given: Remember: Solve:
F= 1.4 kg/m/s m = F
a= 9.8 m/s a
m= ? m = 1.4 N
9.8 m/s2
m = .14 kg F m a

37. Weight and Mass Weight- measure of gravity on an object
Not equal to mass (constant everywhere)
Measured in Newtons
weight = mass x free-fall acceleration (9.8m/s2)
free-fall
m g acceleration w

38. Gravity Force of attraction between 2 objects in the universe
Increases as:
- mass increases
- distance decreases
Affects all matter

39. Gravity Quiz 1
Who experiences more gravity - the astronaut or the politician?
More distance
Less distance

40. Gravity Quiz 2
Which exerts more gravity, your hand or your pencil ?

41. Gravity Quiz 3 Would you weigh more on Earth or Jupiter?
(Hint: Which planet has the greater mass?)

42. Free Fall Acceleration
Occurs when Earth’s gravity is only force acting on an object
In absence of air resistance, all objects accelerate at same rate
g = 9.8 m/s2
g = 9.8 m/s2 g = 9.8 m/s2 g = 9.8 m/s2 g = 9.8 m/s2 g = 9.8 m/s2

43. Air Resistance
Force of air on a moving object which opposes its motion
Aka fluid friction or drag
Depends on objects:
- speed
- surface area
- shape
- density

44. Air Resistance (cont’d)
Terminal velocity=
maximum velocity reached by a falling object
Reached when…
F gravity = F air resistance
(no net force)

45. Projectile Motion Projectile- Any object thrown in air
Only acted on by gravity
Follows parabolic path- trajectory
Has horizontal and
vertical velocities
V oy
V ox

46. Projectile Motion (cont’d)
Horizontal Velocity
depends on inertia
remains constant
Vertical Velocity
depends on gravity
accelerates downward at 9.8 m/s2

47. Projectile Motion Quiz
A moving truck launches a ball vertically (relative to the truck). If the truck maintains a constant horizontal velocity after the launch, where will the ball land (ignore air resistance)?
A) In front of the truck
B) Behind the truck
C) In the truck
Answer: C because horizontal and vertical velocities are
independent of each other

48. Newton’s Laws of Motion
3rd Law of Motion:
When one object exerts a force on a second object, the second object exerts an equal but opposite force on the first.

49. Newton’s Third Law Forces always occur in pairs
Forces in a pair do not act on the same object
Equal forces don’t always have equal effects

50. Newton’s Third Law
Problem: How can a horse pull a cart if the cart is pulling with equal force back on the horse?

51. Newton’s Third Law Answer:
Forces are equal and opposite but are acting on different objects
Forces are not balanced
The movement of the horse depend on the forces working on the horse.

52. Momentum Momentum- quantity of motion = mass x velocity
units: kg x m/s p m v

53. Practice Problem 1
Find the momentum of a bumper car if it has a total mass of 280 kg and a velocity of 3.2 m/s. Given Remember Solve m = 280 kg p = mv v = 3.2 m/s p =(280kg)(3.2m/s) P = ? P = 896 kg  m/s vv p m v

54. Practice Problem 2
The momentum of a second bumper car is 675 kg·m/s. What is its velocity if its total mass is 300 kg? Given Remember Solve p = 675 kg·m/s v = p ÷ m m = 300kg v =(675kg·m/s)÷(300kg) v = ? v = 2.25m/s p m v

55. Conservation of Momentum
Law of Conservation of Momentum:
Total momentum of two or more objects before a collision is the same as it was before the collision (momentum is conserved).

56. Jet Car Challenge 2 skewers 1 balloon 1 cardboard base CHALLENGE:
Construct a car that will travel a least 3 meters using only the following materials:
scissors
tape
4 plastic lids
2 plastic straws
Use your knowledge of Newton’s Laws to make this thing go!