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Physics: Motion. TEXT – SECTION 8.1. Directions. You plan to visit a friends house after school. Your friend tells you that she lives 1 km from school which is only about 25 minutes away if you walk at 2 km/hr. Do you think you could get there?
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Physics: Motion TEXT – SECTION 8.1
Directions • You plan to visit a friends house after school. Your friend tells you that she lives 1 km from school which is only about 25 minutes away if you walk at 2 km/hr. • Do you think you could get there? • Probably NOT…..you need a direction to walk in! • What info is given here? • Answer: time, distance and speed
Scalars vs Vectors • Distance, time and speed are examples of magnitude • Magnitude: the size of a measurement • Scalars: quantities that include a magnitude eg: 5 km/h • Vectors: quantities that describe magnitude and direction 5 km [E]
Distance (d) • A scalar quantity (has no direction) • Describes the length of the actual a path between two points • The SI unit for distance is always in meters (m)
Position (d) • Vector quantity (has direction), SI unit is in meters, (m) • Describes a specific point relative to a reference point • Reference point is the location of an object as seen by an observer from a particular viewpoint. • For example if your viewpoint (aka origin) is “home” determine the following: 1. distance travelled 2. position • A • B
Time and Time Interval • Time Interval describes the duration of an event…how long something takes. • Represented by: t • Time interval is calculated by determining when an event begins ti (initial time) and ends tf (final time) • SI unit for time and time interval is always seconds, (s) • Therefore: t = tf – ti
Calculating the Time Interval • Equation: : t = tf – ti • Eg: What is the time interval from the fire hydrant to the sign? • Answer: = 5 s – 2 s = 3 s Thus, the time interval from the fire hydrant to the sign is 3.
Displacement ( d) • Vector quantity (distance and direction) • Describes the straight line distance and direction from one point to another. • Describes how much an objects position has changed from its origin (starting point). • Eg: if an object ends up where it started, its displacement is always zero. • Equation: d = df - di
Displacement • Equation: d = df - di • What is the displacement of the skateboarder from the fire hydrant to the sign? • Answer = 7 m [E] – 2 m [E] = 5 m [E]
Watch for Signs! • (-) or (+) signs you must memorize these! West East Left Right - + • AND North Up + South Down _
Watch for Signs • Example: Calculate the distance and displacement of the skater below: • Distance: 9m + 5m = 14 m • Displacement: d = df - di = - 5m – (+9m) = - 14 m [W] -14 m [W] since the (-) indicates a westward direction
Uniform Motion • Objects in uniform motion travel in equal displacements in equal time intervals • Objects thus, do not speed up or slow down • Motion Diagram: shows objects position at given times:
Graphing Uniform Motion Position Time Graph • Uniform motion is represented by a straight line • Line of best fit is used
Slope on A Position Time Graph • Slope of a graph refers to whether a line is horizontal or goes up or down at an angle • Slope may be positive, negative or zero • Positive Slope – Slants UP and to the RIGHT • Indicates the objects position is increasing in respect to time away from the origin
Slope on a Position Time Graph • Zero Slope – this is when an object is at rest or stationary • Appears as a straight horizontal line • No change in position
Slope on a Position Time Graph • Negative Slope – slants down to the right • Indicates an object is traveling back to its origin and/or to the left • Eg: a golf ball that has over shot the hole:
Graph this: Position Time Graph & Oscar the Bear Oscar the bear roamed the meadows by day and curled up in his den by night. One morning Oscar awoke feeling famished and so he headed out towards the nearby river, located directly 10 km east for his den. On his way to the river mouth, to his surprise, he stumbled upon a raspberry bush. He decided to stop and gorge on the sweet fruit. Delicious as they were, the raspberries were not enough for Oscar so he continued to make his way east to the river. As he journeyed he noticed some eagles dipping and diving over the river in the distance. Oscar had seen this before and knew that this could only mean one thing; salmon! Excited, Oscar began to run to the river. He ran until he hit the mouth of the riverbank. Oscar walked down and up along the riverbank stopping occasionally to eat. Full as could be, Oscar decided to waddle back home to his den. With the sun setting, Oscar curled up in his den and fell fast asleep.