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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

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 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 motion11
Section 1: Gravity and Motion
  • Examples of Objects in Projectile Motion:
    • A football being passed Water sprayed by a sprinkler
    • Balls being juggled A swimmer diving into water
    • An athlete doing a high jump A 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=acceleration m=mass F=force

 a= FF= m x a

m

 m=F

a

See figure 16 pg. 47

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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