1. Nov. 14, 2017 You need: Clean paper (2) / pencil
HW: Wolf WS, Formula challenge, Ch.2 notes (only 2nd and 3rd had Ch.2)
Warm Up:
Toon Train is traveling at the speed of 10 m/s a the top of a hill. Five seconds later it reaches the bottom of the hill and is moving at 30 m/s. What is the rate of acceleration of Toon Train? (show your work)
I CAN: recognize and define balanced and unbalanced forces.
Nov. 14, 2017

2. In math terms… Distance Speed = Time
A “change in position over time” is the same as saying:
Distance
Speed =
Time

3. D S T Speed = Distance Time Time = Distance Speed
Distance = Speed x Time D S T

4. How can we describe motion?
Motion can be described by:
DISTANCE (how far did it travel?)
TIME (how long did it travel?)
SPEED (how fast did it travel?)
DIRECTION (which way did it go?)
ACCELERATION (does the motion change?)

5. Speed vs. Velocity
SPEED – tells you have fast or slow something is moving (changing position).
Example = 25 km/h
VELOCITY – tells you speed AND DIRECTION! (changing position in a certain direction)
Example = 25 km/h EAST

7. 5 m/s
7.5 m/s
10 m/s
12.5 m/s
14 m/s
12.5 m/s
10.7 m/s
8.75 m/s
6.7 m/s
4 m/s

8. 70 50
Distance (m) 30 10 1 3 5 7 9
Time (sec)

9. Acceleration Acceleration is the CHANGE in speed.
Acc = Speed (final) – Speed (initial)
total time

10. 14 10
Speed (m/s) 6 2 1 3 5 7 9
Time (sec)

13. 13. Goldie Goldfish, a speed swimmer, loves to race around the park’s pond, which is 0.5 miles around. If she can swim 20 laps around the track in 2 hours, what is her average speed?
Speed = Distance
Time
10 miles = =
5 miles / hour
2 hours
Distance = 0.5 miles...for ONE lap
Goldie can go 20 laps…so 20 x 0.5 miles...for total distance

14. 14. It takes Stu, a slimy slug, 20 minutes to travel from his favorite bush to the local trash can (a trip of 30 m), how FAR can he travel in 1 hour (60 min)?
Distance = Speed x time =
1.5 m / min x
1 hour
60 min =
90 meters
Speed = Distance / time
Stu can go 30 meters in 20 min, so…
Speed = Distance
Time
30 meters
1.5 m / min = =
20 min

15. 18. Toon Train is traveling at the speed of 10 m/s a the top of a hill
18. Toon Train is traveling at the speed of 10 m/s a the top of a hill. Five seconds later it reaches the bottom of the hill and is moving at 30 m/s. What is the rate of acceleration of Toon Train?
Acc. = Sp (f) – Sp (i)
Time
30 m/s – 10 m/s
20 m/s = =
5 sec
5 sec
Acc. = 20 m/s
5 sec
Acc. = 4 m/s
1 sec =
4 m/s/s =
4 m/s2

16. Quick Quiz You MAY use your notes and homework.
You may NOT use your textbook or neighbor (or neighbor’s notes).
Bubble answers onto the scan-tron.
#20 is on the board.

17. Which team are you most thankful for?
Imagineers
Seekers
Orient Express
Tigers

18. Chapter 2 - textbook Define force.
What information do you need to know to DESCRIBE a force?
What is the difference between “contact force” and “noncontact force”?
Explain weight.
Explain the relationship between mass and weight.

19. What do you know about force?
What do you need to know to describe a force?
What happens if forces are both acting on the same thing?

20. Let’s try something You have a rope (marked with a twist tie).
Drape it across the desks to a table partner across from you.
Each of you will need to pull on the rope in such a way as to make sure the twist tie does NOT move.
How did you do it?

21. Let’s try again Same scenario.
Drape it across the desks to a table partner across from you.
Each of you will need to pull on the rope in such a way as to make sure the twist tie does move toward ONE of the pair.
How did you do it?

22. What would you call that?
If it doesn’t move?
If it does move?
Sketch an example of each onto your paper.
Give two examples of balanced forces and two examples of unbalanced forces.

23. Introduction to
FORCES

24. A FORCE is a PUSH or PULL in a particular DIRECTION.
FORCES
When you ride a bike, your foot PUSHES against the pedal. The push makes the wheels of the bike move.
When you drop something, it is PULLED to the ground by gravity.
A FORCE is a PUSH or PULL in a particular DIRECTION.

25. FORCES FORCES AFFECT HOW OBJECTS MOVE.
Forces can affect motion in the following ways: They can make objects:
START MOVING
MOVE FASTER
MOVE SLOWER
STOP MOVING
CHANGE DIRECTION
CHANGE SHAPE
BIG SCIENCE IDEA

26. FORCES
Identify each picture as a PUSH or a PULL. Is the force causing a change in speed or direction or both?

27. Forces cause ACCELERATION.
Since forces cause changes in SPEED or DIRECTION of an object, we can say that forces change VELOCITY, so….
Forces cause ACCELERATION.

28. FORCES 1) Strength of the Forces 2) Direction of the Forces
More than one force can act on an object at one time. What happens to the object when forces act depends on 2 things:
1) Strength of the Forces
2) Direction of the Forces

29. FORCES Forces may WORK TOGETHER or OPPOSE each other.
When 2 or more forces act on an object, the forces combine to form a net force.
Forces may WORK TOGETHER
or OPPOSE each other.

30. FORCES
If the forces cancel each other out, and do not cause the object to move, the forces are said to be BALANCED.
If the forces don’t cancel each other out – 1 force is stronger than the others – the forces are UNBALANCED and will cause a CHANGE IN MOTION.

31. MEASURING FORCE The strength of a force is measured in NEWTONS.
The symbol is (N).
We use a SPRING SCALE to measure force.

32. MEASURING FORCE Always “zero” your balance before use.
Pull gently and with constant force.
Practice using your spring scale to drag items across your desk.

33. Try on your own!
Take off a shoe (one per table) – keep your socks ON!!
Use the “mystery tool” to push or pull the shoe across the table.
Flip the shoe so that the laces are down and try again.
Write your observations!

34. Shoe lab
Record the amount of force at the moment the shoe first moves!
Record your data!

35. COMBINING FORCES = 5 N right + 10 N right 5 N right
Two forces in the same direction can add together to produce a larger net force.
5 N
right + =
10 N
right
5 N
right

36. COMBINING FORCES = 5 N right - 5 N left 10 N left
Two forces in opposite directions can subtract to produce a smaller net force in the direction of the larger force.
5 N right - =
5 N left
10 N left

37. COMBINING FORCES 0 N = - 5 N right 5 N left
Two forces may cancel each other out (if equal and opposite) to produce NO NET FORCE.
5 N right
5 N left - =
0 N
(No Net Force)

38. Circle the best answer:
The forces shown above are PUSHING / PULLING forces.
The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.
The forces shown above are EQUAL / NOT EQUAL.
The forces DO / DO NOT balance each other.
The net force is N TO THE RIGHT / N TO THE LEFT / ZERO.
There IS / IS NO motion.

39. Circle the best answer:
7) The forces shown are PULLING / PUSHING forces.
8) The forces shown are WORKING TOGETHER / OPPOSITE FORCES.
9) The forces shown are EQUAL / NOT EQUAL.
10) The forces DO / DO NOT balance each other.
11) The stronger force is pulling RIGHT / LEFT.
12) Motion is the to the RIGHT / LEFT.

40. 50 N
NET FORCE
200 N
150 N
Two movers are trying to move a heavy box. One mover pushes to the right with a force of 150 N. The other mover pushes to the left with a force of 200 N.
a) Draw & label the forces on the diagram.
b) What is the net force? N LEFT
c) Will the box move? YES
d) If yes, in what direction? LEFT

41. 14) Two movers are trying to move a heavy chair
14) Two movers are trying to move a heavy chair. One mover PULLS to the left with a force of 200 N. The other mover PUSHES to the left with a force of 200 N.
a) Draw & label the forces on the diagram.
b) What is the net force?
400 N LEFT
c) Will the chair move?
YES
d) If yes, in what direction?
LEFT
400 N NET FORCE
200 N
200 N

42. MIKE
Four children are fighting over the same toy. Mike is pulling North with a 50 N force, Justin is pulling East with a 40 N force, Chantal is pulling South with a 50 N force, and Tykera is pulling West a 30 N force.
a) Draw & label the forces on the diagram.
b) Is there a net force on the toy?
YES = 10 N EAST
c) In which direction will the toy move?
EAST
d) Who gets the toy?
JUSTIN
50 N
TYKERA
JUSTIN
30 N
40 N
50 N
10 N
Net Force
CHANTAL

43. Try this twist!
Use the spring scale to pull the shoe across the table.
This time, try different surfaces. Have one person hold down the wax paper as someone pulls the shoe across.
Write your observations!
Remember to record the amount of force needed to start motion!

44. FRICTION

45. The force that slows the ball to a stop is FRICTION.
What will happen when the ball is released?
When the ball reaches the bottom of the slope, will it keep moving forever?
The force that slows the ball to a stop is FRICTION.
Since the ball stops, there must be a force acting to slow the ball down.

46. What is Friction?
Friction is a force that two surfaces exert on each other when they rub against each other.
The direction of the friction force is always OPPOSITE to the direction of the motion.
Direction of Motion
Friction Force

47. Direction of Intended Movement
Types of Friction
Static Friction opposes the motion of an object that is at rest
To make the object move, you have to exert a force larger than the force of static friction.
Direction of Intended Movement
Static Friction Force

48. Sliding Friction Force
Types of Friction
Sliding friction occurs when two solids slide over each other.
Sliding friction makes car brakes work and stops athletes from slipping.
Direction of Slide
Sliding Friction Force

49. Types of Friction
Rolling friction occurs when an object rolls across a surface.
Rolling friction is easier to overcome than sliding friction for the same materials.
Direction of Motion
Friction Force

50. Types of Friction
Fluid friction occurs when a solid object moves through a liquid or gas.
Air resistance is a type of fluid friction.
Direction of Motion
Friction Force

51. Which type of friction is slowing down the object in each situation?
You are slipping down a waterslide at Emerald Pointe.
You use a lot of force to slide a desk across the floor.
You’re riding a skateboard down the street and it slowly rolls to a stop.
You try to push the couch, but can’t seem to move it.
FLUID FRICTION
SLIDING FRICTION
ROLLING FRICTION
STATIC FRICTION

52. Friction Thought Questions
Why would you add oil to a rusty bike chain?
Why would you add sand to an icy driveway or road?
Why is it easier to move heavy furniture using a handcart rather than pushing it?
Why would a shoe company be interested in studying friction?
What would happen if we repeated the tug-of-war and one team had only socks on?

53. Review of Friction Forces
Friday, April 28, 2017
Stopped here

54. Review - What is Friction?
Friction is a force that two surfaces exert on each other when they rub against each other.
The direction of the friction force is always OPPOSITE to the direction of the motion.
It SLOWS down moving objects!
Direction of Motion
Friction Force

55. Conclusions Questions
Which surface material created the MOST frictional force?
Which surface material created the LEAST frictional force?
Give an example of a situation where we use a certain surface material to:
a) REDUCE friction
b) INCREASE friction

56. & AIR RESISTANCE The physics of falling
GRAVITY
& AIR RESISTANCE
The physics of falling

57. The Force of Gravity
Gravity is the force that pulls all objects down to the earth.
Rain falls from the sky down to earth…
If you drop a book, it falls to the ground…
If you trip, you’ll fall down…

58. Universal Gravitation
Actually in science, gravity is a force of attraction that acts between ALL objects (the earth, you, the desk, a book)
The force of gravity is much STRONGER for LARGER objects (more mass).

59. Universal Gravitation
Because the Earth is by far, the largest and closest object around, it has the greatest force of attraction...
So, no matter where you are on earth, all things fall to the ground due to gravity…

60. What is “free fall”?
When gravity is the ONLY force acting on an object, it is in free fall.
In that case, gravity is an UNBALANCED FORCE which causes the object to accelerate.

61. Acceleration due to Gravity
Calculate the acceleration of an object in free fall.
A = Final speed – initial speed
time
A = 50 m/s – 0 m/s
5 s
Acceleration = 10 m/s2

62. Objects in Free Fall Do all objects fall at the same rate?
If we dropped a bowling ball and a tennis ball from the same height, which would land first?

63. Question: How does mass affect the speed of a falling object?
Mass and Gravity
April 28, 2017
Question: How does mass affect the speed of a falling object?
Hypothesis: (What do you think will happen AND WHY?)
Observations & Data Collection:
Repeat each trial twice and record your observations.
Ping pong ball vs. Wooden ball:
Wooden ball vs. Metal ball:
Ping pong ball vs. Metal ball:
Conclusion: (One sentence)

64. Objects in Free Fall Do all objects fall at the same rate?
ALL objects in free fall travel at the same rate, regardless of mass!
In free fall, heavy objects and light objects fall at the same rate!

65. So, which will land first?
WHY does the penny land first?
Remember the force that opposes motion (slows things down)? FRICTION!
Falling objects experience friction with the air called AIR RESISTANCE that slows them down.

66. Air Resistance
The larger the object (more surface area), the more air resistance.
That’s why parachutes work! The upward force of the air acting on the LARGE parachute slows you down as you fall.

67. Air Resistance Draw a diagram showing the forces…
Gravity
Draw a diagram showing the forces…
Downward force of gravity is same on both.
Upward force of air resistance is greater on the feather.
The net force (down) is greater on the penny.
Net Force on Penny
Net Force on Feather

68. Without air resistance, all objects would fall at the same rate…
Galileo Drops the Ball
Hammer and Feather Drop on the Moon

69. That’s why astronauts weigh less on the moon!
Gravity on the moon?
The force of gravity is much weaker on the moon because…
It is much farther away from earth.
The moon is much smaller than earth.
That’s why astronauts weigh less on the moon!

70. Gravity Review
Gravity is the force that pulls all objects down to the earth.
When gravity is the ONLY force acting, ALL objects accelerate at a rate of 10 m/s2.
Mass doesn’t matter – in free fall, heavy objects and light objects fall at the same rate!

71. Air Resistance Review
Some objects take longer to fall – they are slowed down by FRICTION with the air called AIR RESISTANCE.
The larger the surface area, the greater the force of air resistance pushing up.
Without air resistance, all objects would fall at the same rate…

72. Draw a free body diagram of the sky diver and label ALL the forces.
Gravity = 1000 N
Air Resistance = 800 N
What is the net force?
Air Resistance = 800 N
Net Force = 200 N
Gravity = 1000 N