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FORCE & MOTION
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OBSERVATION
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Observations · Pay close attention to the following. · Make notes on what you observe. · Do not take anything for granted.
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Motion Observing a displacement of one thing relative to another. Describing Motion All motion is Relative The object moved in relation to the reference object or point.
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Frame of Reference The context or limits of what we are discussing Helps us have a common scope for discussion
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Measurement Defines a scaled common reference Can be replicated Is known and referenced Quantifies the change in position Common measurement scales are: Standard (English/US) Feet, Pounds, etc. Metric Meters, Grams, Liters Internationally accepted system (SI)
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LINEAR MOTION Concepts: Scalars & Vectors
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How Do We Describe “Where”? If objects move, how can we describe… – How far? – How much? – What direction? “How much” or “How far” is the magnitude of motion “What direction” is the direction of motion.
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Two different “How Far’s” Distance – How far? – Scalar – Only measures path Displacement – How far from the start are we now? – What direction is it from the start to finish? – Vector – Measure distance and direction from start point to end point.
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Scalars: Magnitude or Direction Magnitude How big How much What quantity OR Direction Cardinal Degree
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Distance: A Scalar Distance Start Finish
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Vectors: Magnitude & Direction Magnitude How big How much What quantity AND Direction Cardinal Degree
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Displacement: A Vector Displacement Finish Start
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Vector Addition “Connect the dots”
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Vector Addition “Add” vectors to find the net result of the trip. Net Displacement: The sum of the vectors Start Finish Net Displacement Vector
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Finding “Net Displacement” Using Math Add all Vertical vectors Add all horizontal vectors Us Pythagorean Theorem Start Finish Net Displacement Vector
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Start Finish Net Displacement Vector
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Sum of vertical vectors Sum of horizontal vectors Net Displacement a2a2 a b b2b2 c2c2
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RATES Speed, Velocity, Acceleration
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Vectors Are Found Throughout Physics There are three basic measureable properties in science – Mass – Distance – Time Physicists use these to describe the relationships and properties of an objects and their motions.
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Speed Ratio of distance travelled to time taken Distance ÷ Time Scalar quantity No direction Path is important
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Velocity Ratio of displacement to time taken Displacement ÷ Time Vector quantity Measured from start point to end point Disregards path
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Comparing Speed and Velocity Dist. = 24 meters Time = 12 seconds Speed = 2 m/s
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Comparing Speed and Velocity Disp. = 9 meters ENE Time = 3 seconds Velocity = 3 m/s ENE
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Science Problems “What’s your problem with problems?”
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Speedy Velocity Problems “How to work science problems” Jimmy the Frog hops around his pond. His hop-o-meter says he has travelled 36 meters. The sundial says it only took him 20 minutes. What was Jimmy’s speed?
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How to work science problems Step 1: Identify your variables (with units!) Jimmy the Frog hops around his pond. His hop-o- meter says he has travelled 36 meters. The sundial says it only took him 20 minutes. What was Jimmy’s speed ? Distance: 36 meters Time: 20 minutes Speed: ???
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Distance: 36 meters Time: 20 minutes Speed: ???
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How to work science problems Step 2: Write down the equation
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Distance: 36 meters Time: 20 minutes Speed: ???
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How to work science problems Step 3: Change the equation to find the missing variable SpeedWhat do I need to find? No What does the equation solve for? Do I need to change the equation? Speed
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Distance: 36 meters Time: 20 minutes Speed: ???
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How to work science problems Step 4: Substitute variable values into formula. Distance: 36 meters Time: 20 minutes Speed: ???
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Distance: 36 meters Time: 20 minutes Speed: ???
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How to work science problems Step 5: Do (and show!!!) your work
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Distance: 36 meters Time: 20 minutes Speed: ???
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How to work science problems Step 6: Identify your answer Speed = 1.8 m/min.
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Distance: 36 meters Time: 20 minutes Speed: ??? Speed = 1.8 m/min.
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Distance: 36 meters Time: 20 minutes Speed: ??? Speed = 1.8 m/min.
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ACCELERATION It’s all about change
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Acceleration · Ratio of change in velocity to time · (Displacement ÷ Time) ÷ Time · Vector quantity · A change in velocity (direction or magnitude) constitutes acceleration
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GRAPHING MOTION
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Distance Distance/Time or Speed Graphs Speed 3.5 3 2.5 (m) 2 1.5 1 0.5 0 Object 1 1 2 3 4 Time (s)
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Distance/Time or Speed Graphs Speed 3.5 3 2.5 2 1.5 1 0.5 0 Object 1 1 2 3 4 Time (s) Distance (m)
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Distance/Time or Speed Graphs Speed 2.5 2 1.5 1 0.5 0 Object 1 1 2 3 4 Time (s) Distance (m)
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Distance/Time or Speed Graphs Speed 12 10 8686 Object 1 420420 1 2 3 4 5 Time (s) Distance (m)
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Displacement/Time or Velocity Graphs Velocity 3.5 3 2.5 2 1.5 1 0.5 0 Object 1 1 2 3 4 Time (s) Displacement (m)
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Displacement/Time or Velocity Graphs Velocity 1.2 1 0.8 0.6 Object 1 0.4 0.2 0 1 2 3 4 Time (s) (m) Displacement
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Displacement/Time or Velocity Graphs Velocity 3.5 3 2.5 2 1.5 1 0.5 0 Object 1 1 2 3 4 Time (s) (m) Displacement
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Displacement/Time or Velocity Graphs Velocity 14 12 10 8 64206420 Object 1 1 2 3 4 5 6 Time (s) (m) Displacement
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Velocity (m/s) Velocity/Time (Acceleration) Graphs Acceleration 3.5 3 2.5 2 1.5 1 0.5 0 Object 1 1 2 3 4 Time (s)
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Velocity/Time (Acceleration) Graphs Acceleration 2.5 2 1.5 1 0.5 0 Object 1 1 2 3 4 Time (s) Velocity (m/s)
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Momentum
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Physical Properties of Objects Innate Properties Mass Speed Size Density Color Derived Properties Density Speed Weight
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Observations on Objects in Motion Move in a straight line – Unless something pushes them off that line Speed wants to remains constant – Less friction is less loss of “speed” Massive objects are harder to move – Need more push to move
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Observations on Objects in Motion If a moving object hits a non-moving object, the non-moving object is set in motion and the speed of the first moving object is reduced. How? Is there a relationship of properties that may explain this?
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Observations on Objects in Motion What properties of objects seem to be involved? Speed Mass What should we call this Speed-Mass property? Momentum
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Objects & Momentum
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Newton’s Laws
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Newton’s First Law An object will retain it motion unless an outside force acts upon it. Inertia: The resistance to movement of an object relative to its mass.
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Newton’s Second Law An object will accelerate if an unbalanced force is applied to it.
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Newton’s Third Law All forces between two objects exist in equal magnitude and opposite direction Weight of Object Normal Force of Object
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END OF MOTION LECTURE
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