# Motion.  Motion: The change in position of an object as compared with a reference point  Reference point: System of objects that are not moving (stationary)

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Motion

 Motion: The change in position of an object as compared with a reference point  Reference point: System of objects that are not moving (stationary) in respect to one another

 Length of path between 2 points  May not be straight line (shortest path)  Units: meters (m), km, miles, cm, etc.  Ex: Roads/streets we drive

 The direction and length in a straight line from start to end  ALWAYS includes direction from start point  Ex: walk 5 blocks north from McDonald’s  Ex: roller coaster ride displacement = 0

 How fast in a given amount of time 1. Distance traveled by object 2. Time to travel that distance  Units: ◦ m/s ◦ mi/hr or mph ◦ km/hr

 Average Speed - Calculated speed for trip  Ex) Ran marathon at 6 mi/hr  Instantaneous Speed - speed at exact moment  Ex) speedometer reading = 55 mi/hr  Object going an equal distance in equal amounts of time = Constant speed (not speeding up or slowing down)

 Doesn't tell the direction  45 mph  4 m/s

 Expressed in m/s  Speed = Distance/Time  Or S = d/t  Ex: A car traveling at a constant speed and it goes and distance of 645 m in 25 s. What is the car’s speed?  S = d/t  S = 645m/25s  S = 25.8 m/s

 Graphs show speed/velocity  Time (independent variable) -> x-axis  Distance (dependent variable) -> y-axis

 Slope of line = speed or velocity  Straight line = constant speed (cruise control)  Steeper slope = faster speed

 Horizontal (flat) line = object not moving  Exs: stopped at red light, parked, at store

 Negative slope = went backwards (neg. displacement)  Ex: went to store, shopped, and back home

 Measurements:  Speed: m/s, km/h, or m/h  Direction:  N (NE, NW), S (SE, SW), East, and West  Describes both speed and direction of motion  Must give how “fast” and direction the object is going  Ex: 45 km going South

 Can be described as changes in speed, direction, or changes in both  Small value = increasing gradually  Larger value = speeding up more rapidly  The slope of a speed-time graph is acceleration

 Positive Acceleration – velocity increases or speeds up (gives a positive slope  )  Negative Acceleration – velocity decreases or slows down (gives a negative slope  )  Horizontal line – on a velocity-time graph; stays constant, velocity does not change (--- --)

 Any change in how fast or change in direction  Speed up  Slow down  Turn a corner  Go around a curve

 Acceleration = change in velocity/time  a = (final velocity – initial velocity)/time  Measured in meters/second/second  a = vf - vi/t

 Calculating positive acceleration = pos. # (speeding up)  Ex: a = (80m/s – 0m/s)/20s = 4m/s  Calculating negative acceleration = neg. # (slowing down)  Ex: a = (0m/s – 3m/s)/2s = 1.5 m/s

 Causes velocity change  Unit = Newton (N)  Net Force - combo of all forces acting on object  Net force = 0  Either stopped or constant speed

 2 Types of forces: 1. Balanced Forces - net force = 0  Forces cancel out  Ex) Fair tug of war 2. Unbalanced Forces - net force not = 0  One force is stronger  Car vs Train

 Physicist who described relationship between force & motion  3 Laws: Newton’s Laws of Motion

 AKA – Law of Inertia  “An object at rest stays at rest, and an object in motion stays in motion, unless acted upon by an unbalanced force.”  Inertia = tendency of object to stay at rest  Exs: car crashes, magician table cloth trick

1 st Law

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