Describing Motion Concept Notes PDF

 Motion Motion: when an object changes its position. – Dependent on the reference point. Reference point: an indicator that orients you; the place from where you measure, record, or witness an event. – Ex. Consider the reference point when describing the motion of a...

 Motion Motion: when an object changes its position. – Dependent on the reference point. Reference point: an indicator that orients you; the place from where you measure, record, or witness an event. – Ex. Consider the reference point when describing the motion of a car.  Measuring Motion Distance: (d) how far an object has moved. – Can be measured in m, in, ft, mi, etc. Displacement: (Δx) distance and direction of an object’s change in position; difference from starting to ending point. – Ex. If a runner runs around a 400 m track and ends where they started, they have traveled a distance of 400 m, but have been displaced 0 m.  Example #1 If a soccer player runs after his opponent 50 m North, then turns around and chases him 20 m South, what is his distance and displacement? Use the picture to the right to help you. d=? d = 50 + 20 Δx = ? d = 70 m 20 m 50 m Δx = 50 – 20 Δx = 30 m North  Measuring Motion Sometimes finding displacement isn’t as easy. If an object travels at a right angle, the Pythagorean b c Δx theorem is used to find the displacement. a a +b =c 2 2 2 – c (the hypotenuse of the right triangle) would be the displacement (Δx) – Note: This will not need to be used every time you find displacement!!  Example #2 A delivery truck drives 4 miles b c Δx West before turning right and 6 miles driving 6 miles North to make a delivery. Find the delivery truck’s a distance and displacement. 4 miles a = 4 miles d=4+6 a2 + b 2 = c 2 c = 7.21 d = 10 mi 42 + 6 2 = c 2 Δx = 7.21 mi b = 6 miles 16 + 36 = c2 Northwest c = Δx = ? √ 52 = √ c 2 a2 + b2 = c2 7.21 = c  Measuring Motion Speed: (s) the distance an object travels per unit of time. – Can be measured in m/s, mi/hr, ft/min, km/hr, etc. d s= t  Calculating Speed Example #3: Suppose you ran 2 km in 10 min. With what speed did you run? s=? s = 2 km d = 2 km 10 min t = 10 min s=d s = 0.2 km/min t  Calculating Speed Example #4: Sound travels at 343 m/s through dry air. If a lightning bolt strikes the ground 2000 m away from you, how long will it take for the sound to reach you? t=? t = 2000 m s = 343 m/s 343 m/s d = 2 km 1000 m = 2000 m t = 5.83 s 1 km (t) s = d (t) t ts=d s s t=d s  Velocity Velocity: (v) the speed of an object and the direction of its motion. – Speed can remain constant and velocity change if the object is changing direction. – Calculated the same as speed, just must include direction in your answer!! x v= t  Practice Time 1. A girl is training to run a 5k (3.1 mile) race. If she runs a trial race in 0.5 hours, what is her average speed? Answer: s = 6.2 mi/hr or 10 km/hr 2. An elevator at a museum can travel 210 m upwards in 35 s. What is the elevator’s velocity? Answer: v = 6 m/s upwards 3. How far does a car travel in.75 hrs if it is moving at a constant speed of 45 mi/hr? Answer: d = 33.75 mi 4. If a motorcycle is moving at a constant speed down the highway of 40 km/hr, how long would it take the motorcycle to travel 10 km? Answer: t = 0.25 hr  Graphing Motion Graphs can visually help us to understand an object’s motion. Slope: the steepness of a line. – Calculated as rise = Δy run Δx On a distance vs. time graph, this means… – Calculated as rise = Δy = distance run Δx time Therefore on a distance vs. time graph, the slope = speed. Graphing Motion Describe the motion of each graph. The object The object is moving is moving at a at a constant constant speed, speed, away from coming the towards the reference reference point. point. The object The object is speeding is slowing up, due to down, due the line to the line becoming leveling steeper. out.  Graphing Motion Sketch a graph that would show an object not moving. Sketch a graph that would show an object moving at a constant speed, stopping, then speeding up.