Chapter 2 forces in motion
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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

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Chapter 2 Forces in Motion

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Chapter 2 forces in motion

Chapter 2 Forces in Motion

Gravity and Motion

Newton’s Laws of Motion


Section 1 gravity and 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 motion1

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 motion2

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 motion3

Section 1: Gravity and Motion


Section 1 gravity and motion4

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 motion5

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 motion6

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 motion7

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 motion8

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 motion9

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 motion10

Section 1: Gravity and Motion


Section 1 gravity and motion11

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

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 motion1

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 motion2

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 motion3

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 motion4

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 motion5

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 motion6

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 motion7

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 motion8

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 motion9

Section 2: Newton’s Laws of Motion


Section 2 newton s laws of motion10

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 motion11

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 motion12

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 motion13

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 motion14

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 motion15

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 motion16

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


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