# Chapter 2 Forces in Motion - PowerPoint PPT Presentation

1 / 30

Chapter 2 Forces in Motion. Gravity and Motion Newton’s Laws of Motion. Section 1: Gravity and Motion. All Objects Fall with the Same Acceleration

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Chapter 2 Forces in Motion

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

## Chapter 2 Forces in Motion

Gravity and Motion

Newton’s Laws of Motion

### Section 1: Gravity and Motion

• All Objects Fall with the Same Acceleration

• **Galileo’s experiment: 2 cannon balls of different weight but the same size. Dropped them off the Leaning Tower of Pisa. Hit Ground at same time.

• Video clip

• changed peoples idea about gravity and falling objects.

### Section 1: Gravity and Motion

• Acceleration Due to gravity

• objects fall to the ground at the same rate because of acceleration due to gravity.

• **See Figure 1 pg.36

• Ping Pong vs. golf ball…who will win???

### Section 1: Gravity and Motion

• Accelerating at a constant rate

• All objects accelerate toward the earth at a rate of 9.8 m/s/s downward

• **See figure 2 pg. 37

### Section 1: Gravity and Motion

• Galileo’s experiment on falling objects clip

• Math Break pg 37

• 1. Δ v=9.8 m/s/s x 2s=_________

• 2. Δ v=9.8 m/s/s x ___=_______

### Section 1: Gravity and Motion

• Air Resistance Slows Down Acceleration

• Crumpled paper and flat sheet example. What happens????

• Air resistance:fluid friction

• occurs between the surface of the object and the surrounding air.

• Air resistance Affects Some Objects More Than Others

• Depends on Size and Shape of the object!!!!

• Ex. Crumpled piece of paper dropped at the same time as a full sheet of paper.

--On Earth ALL OBJECTS ARE AFFECTED BY AIR RESISTANCE

• **See figure 3 pg. 38 video clip on falling

### Section 1: Gravity and Motion

• Acceleration Stops at the Terminal Velocity

• Terminal velocity:object falling at a constant velocity (not changing)

• upward force of air resistance=downward force of gravity (no more acceleration)

• Video Clip

• Terminal velocity a good thing?????

• **Hailstones…no air resistance then they would hit at 350 m/s.

### Section 1: Gravity and Motion

• Free Fall Occurs When There is No Air Resistance

• Free Fall:falling object that only gravity is acting on it (no air resistance).

• Video clip

• Orbiting Objects Are in Free Fall

• Floating Astronauts are in “free fall”

### Section 1: Gravity and Motion

• Two Motions Combine to Cause free fall

• **See Figure 7 pg. 40 How an Orbit is formed (spaceship)

• Orbit:an object traveling in a circular or nearly circular path around another object.

• Why doesn’t the moon fall down? Video clip

• The Role of Gravity in Orbiting

• Centripetal Force:unbalanced force that causes objects to move in a circular path.

• **See Figure 8 pg. 40 (Example the moon)

### Section 1: Gravity and Motion

• Projectile Motion and Gravity

• Projectile Motion:the curved path an object follows when thrown or propelled near the surface of the Earth.

• **See Figure 9 pg. 41

### Section 1: Gravity and Motion

• Examples of Objects in Projectile Motion:

• A football being passedWater sprayed by a sprinkler

• Balls being juggledA swimmer diving into water

• An athlete doing a high jumpA leaping frog

• Horizontal Motion

• motion that is parallel to the ground

• example: throwing a ball

• Vertical Motion

• motion that is perpendicular to the ground

• Example: throwing a dart to a bulls eye

• Gravity Pulls objects in projectile motion down with an acceleration of 9.8 m/s/s (if no air resistance)

• **See Figure 10 pg.42

### Section 2: Newton’s Laws of Motion

BrainPop—Issac Newton

BrainPop—Newton’s Laws of Motion

Newton’s First Law of Motion

Definition: An object at rest and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force

### Section 2: Newton’s Laws of Motion

• Part 1: Objects at Rest

• anything not moving will stay still until an unbalanced force moves it.

• Ex. A chair in the middle of the room will not move until you push it. See Figure 11 pg.43

### Section 2: Newton’s Laws of Motion

• Part 2: Objects in motion

• anything moving will stay moving until an unbalanced force stops or changes the direction it was moving.

• Ex. Bumper Cars—car stops you fly forward. See Figure 12 pg.44

### Section 2: Newton’s Laws of Motion

• Friction and Newton’s First Law

• once you push your chair it should sail across the room forever right? No! The unbalanced force stopping it is FRICTION!

• *****Turn to pg. 44 and answer the APPLY Stopping Motion question

### Section 2: Newton’s Laws of Motion

• Inertia is Related to Mass

• Inertia: the tendency of all objects to resist any change in motion.

• Mass Is a Measure of Inertia

• Small mass=less inertia than a large mass object.

• Ex. Playing softball with a bowling ball See Figure 13 pg. 45**DO SELF CHECK pg. 45

### Section 2: Newton’s Laws of Motion

Newton’s Second Law of Motion

Definition:The acceleration of an object depends on the mass of the object and the amount of force applied.

### Section 2: Newton’s Laws of Motion

• Part 1: Acceleration Depends on Mass

• Using the same amount of force to push a near empty grocery cart and full grocery cart.

• Which one will accelerate faster?

• See figure 14 pg. 46

### Section 2: Newton’s Laws of Motion

• Part 2: Acceleration Depends on Force

• Giving a cart a soft push verses a large push.

• Which will accelerate faster?

• See figure 15 pg. 46

### Section 2: Newton’s Laws of Motion

Expressing Newton’s Second Law Mathematically

a=accelerationm=massF=force

a= FF= m x a

m

m=F

a

See figure 16 pg. 47

### Section 2: Newton’s Laws of Motion

• Newton’s Third Law of Motion

• Definition: Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

• See Figure 17 pg. 48

• action force=swimmers hands pushing on the water

• reaction force=water pushing back on hands

• Ex. Your weight pushing on a chair, chair pushing Up

### Section 2: Newton’s Laws of Motion

• Force Pairs Do Not Act on the Same Object

• if they acted the same the net force would be ZERO=no motion!!!!!

### Section 2: Newton’s Laws of Motion

• The Effect of a Reaction Can Be Difficult to See

• See figure 18 pg. 49

• Action force—ball falling to Earth

• Reaction force—Earth being pulled toward the ball

• Why can you not see it?

• the force on the Earth=the force on the ball

• Earth’s mass is greater than ball

• Acceleration of the Earth is much smaller than the acceleration of the ball cannot see or feel it

### Section 2: Newton’s Laws of Motion

• More Examples of Action and Reaction Force Pairs

• See pictures bottom of pg. 49

• Momentum Is a Property of Moving Objects

• Compact car and large truck traveling at the same velocity.

• Which will take longer to stop?

• 2 compact cars: car 1 velocity is 10 m/s east; car 2 20 m/s east. Which will take longer to stop?

### Section 2: Newton’s Laws of Motion

• Momentum: a property of a moving object that depends on the object’s mass and velocity.

• **the more momentum an object has the harder it is to stop.

• Momentum formula: p= m x v

• units for momentum are kg x m/s

• Example: Find the momentum of an 80 kg basketball player driving to the basket with a constant velocity of 8 m/s.

### Section 2: Newton’s Laws of Motion

• Momentum is Conserved

• moving object hits another object, some or all of the momentum of the 1st object is transferred to the other object.

• If only some of the momentum is transferred then the rest of the momentum stays with the 1st object.

• See figure 19 pg. 50

• Ex. Pool and bowling

### Section 2: Newton’s Laws of Motion

Conservation of Momentum and Newton’s 3rd law

• billiard ball: the cue(white) ball hit the billiard ball with a certain amount of force (action force). The reaction force was = but opposite force exerted by the billiard ball on the cue ball.

• Action force made the ball start moving; reaction force made it stop moving.

• See figure 20 pg. 51