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A change in position relative to some reference point during a period of time. Motion.

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Presentation on theme: "A change in position relative to some reference point during a period of time. Motion."— Presentation transcript:

1 A change in position relative to some reference point during a period of time. Motion

2 Rate at which an object moves Speed = distance/time Units: m/sec, km/hr, mi/hr. Speed d s t

3 Instantaneous Speed – speed at a given instant. Average Speed = distance/ time. Describes speed of motion when speed is changing. Constant Speed – speed that doesnt change. Types of Speed

4 Speed Problems What is the speed of a cyclist who travels 50 meters in 25 seconds? S = d/t You are in a car traveling an average speed of 60 km/hr. The total trip is 240 km. How long does the trip take? t = d/s 50 m/25 s2 m/s 240 km/60 km/hr 4 hrs.

5 Distance -Time Graphs Distance (m) Time (sec) Distance (m)

6 Speed in a given direction. Uses: Navigation (airplanes, ships), weather, etc. Vector quantity – represented graphically by arrows ( ). –Length = magnitude –Arrowhead = Velocity direction

7 If you row a boat upstream at 10 km/hr and the river has a downstream velocity of 5 km/hr, you are actually moving at what velocity? Velocity Problem 10 km/hr upstream 5 km/hr downstream 5 km/hr upstream =

8 Rate of change in velocity. Really a description of how fast you can go in a certain amount of time. Good acceleration is being quick to change. Acceleration

9 Examples: speeding up (+ acc.), slowing down (- acc.), or changing direction. Acc. = final velocity – original velocity/time. Units: m/sec/sec Represented by a Velocity – Time Graph Acceleration

10 Velocity vs. Time Graphs Time (sec) Velocity (m/s) Time (sec) Velocity (m/s) Time (sec) Velocity (m/s) Time (sec) Velocity (m/s)

11 A car increases its speed from 60 km/hr to 80 km/hr in 4 seconds. What is the cars acceleration? Acceleration Problem 80 km/hr – 60 km/hr 4 sec. 1 st second – 65 km/hr 2 nd second – 70 km/hr 3 rd second – 75 km/hr 4 th second – 80 km/hr 5 km/hr/sec. Acc = Δ velocity time

12 Rates of Motion Table RatesDefinitionEquationUnitGraph Speed Velocity Acceleration

13 Acceleration on an object caused by gravity. Gravitational Acceleration

14 Falling Objects Free fall – considers only gravity & neglects air resistance. All falling objects accelerate at the same rate, regardless of their masses m/sec/sec or 32 ft./sec/sec. on earth. - velocity increases 9.8 m/s each second. - distance fallen – increases mathematically

15 Instantaneous speed v f = v i + at Distance fallen d = v i t + ½at 2 Average speed v = v i + v f Uniform Motion Equations 2

16 Objects Thrown Straight Up

17 Graphing Free Fall Distance (m) Time (sec) velocity (m) Time (sec)

18 Air resistance noticeably alters the motion of things like falling feathers or pieces of paper. Less noticeably on more compact objects. e.g. stones, balls Air Resistance on Falling Objects


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