1. Physical Science
Forces

2. The Nature of Force By definition, a Force is a push or a pull.
Just like Velocity & Acceleration Forces have both
magnitude and direction
components

3. Forces
A force causes an object to move, accelerate, change speed, or direction
Forces are represented by:
Arrows
Direction
Strength
represented by the length of the arrow

4. Balanced & Unbalanced Forces
Balanced forces – opposite and equal forces acting on the same object
result in NO motion of the object
Unbalanced forces – two or more forces of unequal strength or direction acting upon on an object
results in motion of the object

5. Balanced or Unbalanced Forces?

6. Force/Free body diagrams (to show forces)
used to show the relative magnitude and direction of all forces acting upon an object in a given situation.
a special example of vector diagram
size of the arrow represents
amount of force

7. Force / Free-body Diagrams
direction of the arrow shows the direction which the force is acting
each force arrow is labeled
The object is usually represented by a box. Force arrows are drawn from the center of the box outward in the direction which the force is acting.
(look at types of forces also)

8. Combining Forces
Net force: All forces are added or subtracted to create one total force
If net force is Zero then there is no change in motion.
If there is a net force there is an acceleration

9. Force Problem
What is the net force on an object being pulled toward the west with a force of 30N and another force pulling the object toward the east with a force of 75N?

10. Friction
a force that opposes the motion of objects that touch as they move past each other
acts at the surface where objects are in contact
All moving objects encounter friction
Without it most motion would be impossible
4 types, static, sliding, rolling, fluid

11. Static Friction The force that keeps an object from moving
It is the largest frictional force
Always opposite direction of the applied force
Pushing a Car
Walking

12. Sliding Friction
Once the object is in motion it experiences sliding friction
Opposite direction from applied force
Less than static friction so less force is needed to keep it in motion

13. Rolling Friction
As something rolls, the object and floor bend slightly
This bend causes rolling friction
It is a much smaller force than static friction
As much as 1000 times smaller
Allows you to move heavy objects
Ball bearings reduce friction

14. Fluid Friction It opposes the motion in the liquid
Like swimming, it is hard to move
If you are in the air, fluid friction is called air resistance
At higher speeds it is very noticable

15. Force of Gravity a force that acts between two objects
an attractive force, pulls objects together
causes objects to accelerate downward
Falling objects, gravity pulls down, What pushes up?
air resistance acts in opposite direction
Terminal Velocity- when Gravity and air resistance cancel each other out (velocity of falling body becomes constant)
Skydiving and falcons
Forces Montage

16. May the forces be with you and not against you!!

17. Terminal Velocity
See elephant problem on page 10 and 11 of Netwon’s laws Smart Notebook file!!

18. Projectile Motion When an object not only goes up and down but out
It is a curved path
Air resistance and gravity are the only forces acting on a projectile
What falls faster, an object that falls straight down, or one that has a horizontal velocity?
Myth busters bullet #2
This one shows the end?

19. Newton’s Laws of Motion
Begins Here!!

20. Great Scientists
Aristotle- Incorrectly said force was required to keep an object in constant motion
Galileo- with no resistance objects would move indefinitely
Newton- based on Galileo’s findings he came up with his law’s of motion

21. Newton’s 1st Law of Motion
AKA The Law of Inertia
Inertia- an objects tendency to resist
changes in motion
an object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity until acted on by another force.
Remember:
The greater the mass of an object the greater the inertia

22. Eureka Inertia Video
Eureka Inertia Video

23. Check your Understanding on Newton’s first law

24. You need to remember this about Inertia!!!
Mass is the measure of inertia of an object!!!
So, which would have more inertia?
0.1 kg baseball traveling at 20 m/s
5 kg bowling ball traveling at 3 m/s
10 kg sled traveling at 0 m/s
0.001 kg bumblebee traveling at 2 m/s
Which would have the least?

25. Newton’s 2nd Law
The acceleration of an object is equal to the net force acting on it divided by the objects mass
A= F/m so F=ma
Acceleration is always in the same direction of the net force
An object will have greater acceleration if a greater force is applied

26. Newton’s Second Law of Motion F=ma
Force = mass x acceleration
F=ma ; a= F/m ; m= F/a
What is the basic unit for mass?
Kilogram
What is the basic unit for acceleration?
Meter/sec/sec
Therefore the basic unit for Force is
(kilogram)( meter/sec/sec)
An object with a mass of 1 kg accelerating at 1 m/s/s has a force of 1 Newton

27. Eureka – Weight vs. Mass

28. Newton’s 2nd Law & Force of Gravity
Have you heard of the FORCE of gravity?
Gravity: the force that pulls objects towards each other
Since gravity is a force it also obeys Newton’s second law
F=ma
Since objects fall at the same speed, their acceleration is the same.
All objects accelerate at the rate. Here on Earth the rate is:
Ag=9.8 m/s2 Or
Ag=32 ft/s2
With this experiment, Galileo proved Aristotle wrong
Air resistance keeps things from falling equally
With this experiment, Apollo 15 astronauts proved Galileo right.
(link to You Tube)

29. Elephant and Terminal Velocity

30. Weight and Mass Weight is the force of gravity acting on an object
Weight (N) = mass (g) x acceleration of gravity (m/s2)
Note: just a version of F=ma, F = mass x gravity
FYI:
1 pound = Newtons
so 1/4 lb is slightly more that 1 N
so a 1/4 lb burger is a "Newton" burger

31. Newton’s 2nd Law & Weight
F=ma
So, weight is a type of Force
The formula for weight: Weight = mass x Ag
Since Ag= 9.8 m/s2 then
Weight = mass x 9.8 m/s2
Remember:
1 newton = 0.22 pounds

32. Your weight on other planets & 3 different types of stars

33. Newton’s 2nd Law

34. Math Practice
A boy pushes forward a cart of groceries with a total mass of 40.0 kg. What is the acceleration of the cart if the net force on the cart is 60.0 N?
What is the upward acceleration of a helicopter with a mass of 5000 kg if a force of 10,000 N acts on it in an upward direction?

35. An automobile with a mass of 1200 kg accelerates at a rate of 3
An automobile with a mass of 1200 kg accelerates at a rate of 3.0 m/s2 in the forward direction. What is the net force acting on the automobile?
A 25-N force accelerates a boy in a wheelchair at 0.5 m/s2 What is the mass of the boy and the wheelchair?

36. During a test crash, an air bag inflates to stop a dummy’s forward motion. The dummy’s mass is 75 kg. If the net force on the dummy is 825 N toward the rear of the car, what is the dummy’s deceleration?

37. A bicycle takes 8.0 seconds to accelerate at a constant rate from rest to a speed of 4.0 m/s. If the mass of the bicycle and rider together is 85 kg, what is the net force acting on the bicycle? (Hint: First calculate the acceleration.)
a=(vf-vi)/t
= (4.0 m/s) / 8.0 s
= 0.50 m/s2
F=ma
= 85 kg x 0.50 m/s2
= 43 N

38. Eureka – Acceleration I
Eureka – Acceleration II

39. Begin Newton’s Laws Lab
Talk about rules, etc.

40. Forces Problem Worksheet
Have any questions before we take your quiz?

41. Newton’s 3rd Law of Motion:
For every action there is an equal & opposite reaction.
This means every time a force is applied in one direction an equal force is applied in the opposite direction.
If an object is not in motion, then all forces acting on it are balanced and the net force is zero!

42. Action-Reaction Forces
If you push against a wall it pushes back
These forces can cause motion, like a swimmer
They do not cancel each other out, because they act on different objects.
2 ice skaters

43. Rocket man video clip (stop after balloon)
Space Walk

44. Momentum The product of an object’s mass x velocity
Influences how easily an object can be stopped
High velocity or high mass cause a high momentum
For some reason, maybe because mass is designated as “m” in formulas, momentum is designated as “p”.
Therefore: p = mv
The unit for mass is kg, the unit for velocity is meter/second, therefore the unit for momentum is kg m/sec

45. Which has more momentum?
a kg golf ball with a speed of 60.0 m/s
a 7.0 kg bowling ball with a speed of 6.0 m/s
.046 kg x 60.0 m/s = 2.8 kg m/s
7.0 kg x 6.0 = 42 kg m/s

46. Conservation of Momentum:
When two or more objects interact (collide) the total momentum before the collision is equal to the total momentum after the collision
If no net force acts on a system, then the total momentum of the system does not change
In a closed system, loss of momentum of one object equals the gain in momentum of another object

47. Momentum – 2 moving objects
During this collision the speed of both box cars changes. The total momentum remains constant before & after the collision. The masses of both cars is the same so the velocity of the red car is transferred to the blue car.

48. Momentum – 1 moving object
During this collision the speed red car is transferred to the blue car. The total momentum remains constant before & after the collision. The masses of both cars is the same so the velocity of the red car is transferred to the blue car.

49. Momentum – 2 connected objects
After this collision, the coupled cars make one object w/ a total mass of 60,000 kg. Since the momentum after the collision must equal the momentum before, the velocity must change. In this case the velocity is reduced from 10 m/sec. to 5 m/sec.

50. Momentum Videos
Bill Nye – Momentum
Momentum and collisions video clip

51. Data Analysis – Momentum

52. Questions that make you go Hmmmmmmm….
1. Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?
When you pull up on the handlebars, the handlebars push down on you, and this force is transmitted to the pedals.
2. Lets say you are weighing yourself on a set of bathroom scales. You are standing next to the sink in the bathroom. If at the same time while you are standing on the scales you reach under the sink and pull up on the sink, will the scales register your weight to be more or less than what they would register if you didn't pull up on the sink?
the scales would register heavy. Since you are lifting up on the sink, the sink is pushing down on you with an equal but opposite force and this would be transmitted to the scales.

53. 3. Lets repeat the question in the situation above except that you push down on the top of the sink instead of pulling up on the bottom of the sink. What will your weight be this time compared to what it would be if you did not push down on the sink?
The scales would register lighter. Since you are pushing down on the sink it is pushing up on you with an equal force which tends to lift you up off the scales some and therefore they register light.

54. Eureka – Momentum (Speed)

55. Forces that can be found anywhere in the universe
Universal Forces
Forces that can be found anywhere in the universe

56. Electromagnetic Force
Electric and Magnetic Forces are the only forces that can both attract and repel
Electric forces- between charged particle, positive attracted to negative
Clothes in a dryer
Magnetic forces- N and S poles, opposites attract, likes repel

57. Nuclear Forces
Two forces- a strong and a weak force hold an atom together
The strong nuclear force overcomes the protons repulsion force
This force is over 100x stronger than electric forces
The weak force is involved in radioactive processes

58. Gravitational Force Attractive force between any two masses
This force is very small compared to all the rest
Newton came up with the Law of Universal Gravitation, which explains how we can find the gravitational force of any object
A large mass is required for gravity to be felt

59. Gravity is relational to distance
The further apart two objects are the less the gravitational force
Gravity still has pull over millions and millions of miles apart
As distance doubles the force gets quartered

60. Eureka - Gravity

61. The Earth Moon System
The moon stays in orbit because of Earth’s gravity
It works very similar to a centripetal force
It pulls in on an object
So as the moon follows this circular path, it’s gravitational force has an affect on Earth.

62. Satellites Satellites stay in orbit with centripetal force of gravity
If it were to slow down it would lose altitude

63. Physical Science Formula Reference Sheet

64. Eureka - Mass

65. Tacoma Bridge Collapse

66. Newton’s Laws Tutorial
Having problems? Try doing this tutorial:

67. Video Clips on Newton’s Laws in case you need more!!!
Newton’s Laws of Motion
Another Newton’s Laws of Motion Video