1. Forces and Motion
Chapter 12

2. Inquiry activity (Individual work)
Follow the directions on page 355 of your textbook
Answer the questions
Label it as Penny Lab and turn it in.

3. A push or a pull exerted on an object
Forces
Sec. 12.1
Measured in Newton, N
Examples: Wind, Gravity
Represented with an arrow
The length of the arrow represents the strength of the force

4. Forces in the same direction add together
Combining Forces
Forces in the same direction add together
Forces in opposite directions subtract from each other
Net Force = Overall Force
Balanced Forces
Equal in size
10 N
10 N
Net Force

5. Result in NO movement Balanced Forces cont. 150 N Ex: Standing still
Unbalanced Forces
Not equal in size
5 N
10 N
15 N
Net Force
Ex: Tug-of-War

6. Result in movement
Unbalanced Forces cont.
20 N
30 N
10 N
Net force

7. Friction
Force that opposes motion of objects that touch
friction

8. Types of Friction
Static friction: the force that acts on objects that are not moving
*Always acts in an opposite direction
Ex. Balloon, dryer sheet

9. 2. Sliding Friction: Caused by two object sliding over each other.
Types of Friction
2. Sliding Friction: Caused by two object sliding over each other.
Ex. Slide, Sled, Carpet Burn

10. Quick Lab on sliding friction
We are now going to do the quick lab found on page 360 in your textbook.
You will be working in pairs that I will assign.
Make a data table to record your data that includes eraser with sticky note and eraser without sticky note and 3 trials and the average distance of each eraser.
Answer the questions
Turn this lab in to me

11. Types of Friction
3. Rolling Friction: Caused by two objects rolling over each other.
Ex. Roller skates, car tires, ball

12. Types of Friction
4. Fluid Friction: force that opposes the motion of an object through a fluid
Ex. Submarine, Cake Batter

13. Interactive forces

14. Air Resistance
Fluid Friction acting on an object moving through the air
Examples: Speed Skaters

15. Gravity Force of attraction between two objects that have mass.
Attractive Force - pulls objects together

16. Gravity
On Earth gravity is a constant
9.8 m/s2.

17. Gravitational Forces on the Planets The planet with the strongest gravitational attraction at its surface is Jupiter. Although Saturn, Uranus, and Neptune are also very massive planets, their gravitational forces are about the same as Earth. This is because the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared.

19. Falling Objects Gravity causes objects to accelerate
downward, whereas air resistance acts
in the direction opposite to the
motion and reduces acceleration.

20. Terminal Velocity
Constant velocity of a falling object when the force of air resistance equals the force of gravity.

21. Projectile Motion
The motion of a falling object after it is given an initial forward velocity.
Air resistance and gravity are the only forces acting on a projectile.

22. Newton’s three laws of motion demonstrated

23. Ex. Resting Soccer Ball Newton’s 1st law of motion Law of Inertia
Sec. 12.2
Law of Inertia
“An object at rest stays at rest, and an object in motion stays in motion, unless acted upon by an outside force.”
Ex. Resting Soccer Ball

24. Inertia
Newton’s first law of motion is sometimes called the law of inertia
Inertia is the tendency of an object to resist change in its motion

25. Youtube newton’s cradles

26. Demos performed
Quarters on a card falling into a jar when card is thumped.
Marker falling into a jar when the card is thumped.
Pen falling into a bottle when hoop is removed.
Egg in the beaker with cookie sheet.

27. Newton’s 2nd law of motion
“When a force is applied to an object, the object accelerates in the direction of the force applied.”
Acceleration=Net Force/Mass
Mass is a measure of the inertia of an object and depends on the amount of matter the object contains

28. Ex. How much force in needed to accelerate a 10 kg object at 2 m/s2?
a = 2 m/s2
m = 10kg
F = ?
Formula: a = F/m
2 = F/ F = 20 N

29. If a 100 newton force is applied to a 5 kg object, how quickly will it accelerate?
Newton’s 2nd law of motion
Formula: a = F/m
a = 100/5
a= 20 m/s2
F = 100 N
m = 5 kg
a = ?

30. Weight A measure of the force of gravity acting on an object
Weight = mass x acceleration due to gravity
W = mg

31. Weight = mass x acceleration due to gravity =112 kg x 9.8 m/s2
If an astronaut has a mass of 112 kilograms, what is his weight on Earth?
Weight = mass x acceleration due to gravity
=112 kg x 9.8 m/s2
=1100 kg m/s2
=1100 N

32. Math practice problems
1. What is the acceleration of a 1,500 Kg truck with a net force of 7,500 N? 2. A runner with a mass of 60Kg accelerates at 2.2m/s2. What is the runner’s net force? 3. Find the mass of a flying discus that has a net force of 1.05N and accelerates at 3.5m/s2. 4. Ian has a mass of 58Kg. What is his weight?

33. Ex. Bumper Cars Newton’s 3rd law of motion Sec. 12.3
“For every action, there is an equal and opposite reaction.”
Ex. Bumper Cars

34. The single cart accelerates eight times faster than the chain of eight carts.

35. Momentum The product of an object’s mass and its velocity
A large momentum is hard to stop
The momentum of an object at rest is zero
Momentum = Mass x Velocity
Units are kg m/s

36. Which has more momentum, a 0. 046 kg golf ball with a speed of 60
Which has more momentum, a kg golf ball with a speed of 60.0 m/s, or a 7.0 kg bowling ball with a speed of 6.0 m/s?
Momentumgolf ball = kg x 60.0 m/s=2.8 kg m/s
Momentumbowling ball = 7.0 kg x 6.0 m/s = 42 kg m/s
The bowling bowl has more momentum.

37. Law of Conservation of Momentum
If no net force acts on a system, then the total momentum of the system does not change.

38. The total momentum of the train cars does not change-momentum is conserved.

39. Practice problems
How much force is needed to make a 150kg object accelerate at a rate of 1 m/s2?
How much does a 50 kg person weigh if the acceleration due to gravity is 9.8 m/s2?
What is the mass of a car that weighs 140,000 N?
What is the acceleration of a 150 kg object when 1,500 N is applied?
Calculate Dave’s acceleration knowing that in a race he starts from rest and reaches a speed of 15.3m/s in 4.71 s.

40. Quizzes on forces and motion
After I show the video you need to click on this link and take the 6 practice quizzes.
You also need to take the vocabulary quiz on the same page.

41. Sec. 12.4 Universal forces Electromagnetic Forces
Electric Forces-act between charged objects or particles
Magnetic Forces-act on certain metals, on the poles of magnets, and on moving charges
Electric and magnetic forces are the only forces that can both attract and repel

42. Nuclear forces Act within the nucleus to hold it together
Strong Nuclear Force- a powerful force of attraction that acts only on the neutrons and protons in the nucleus
Weak Nuclear Force- acts only over a short range

43. Gravitational Force
An attractive force that acts between any two masses
Newton’s Law of Universal Gravitation- “every object in the universe attracts every other object”
Weakest, but most effective force

45. Centripetal Force
A center-directed force that continuously changes the direction of an object to make it move in a circle
The result of a centripetal force is a circular path of the object

46. The moon’s inertia and the gravitational pull of the Earth result in a circular orbit.

47. Satellites in Orbit Satellites need only a centripetal force
provided by gravity and its inertia to stay in orbit
Satellites in low orbit are slowed by friction with the Earth’s atmosphere
TEST ON CHAPTER 12 Next class meeting