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Physical Science

Physical Science. Chapter 11 – Part 1 Non-accelerated Motion Chapter 11.1-11.2. Frame of Reference. A system of objects that are not moving with respect to one another A reference point or system BASICALLY …. Something unchanging to measure things from

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Physical Science

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  1. Physical Science Chapter 11 – Part 1 Non-accelerated Motion Chapter 11.1-11.2

  2. Frame of Reference • A system of objects that are not moving with respect to one another • A reference point or system • BASICALLY …. Something unchanging to measure things from • Good frames of reference for measuring the motion of a car… • The Earth, the road, buildings, trees • Bad frames of reference for measuring the motion of a car…. • Clouds, other cars on the road, bikers, flying birds

  3. Relative Motion • Movement in relation to a frame of reference • All Motion is Relative • This means… all motion is based on someone’s or something’s perspective • Examples • School busses • Cars on highway • LabQuest

  4. Relative Motion Or a more recent example

  5. Measuring Distance • Length of a path between two points • When an object moves in a straight line, the distance is the length of a line connecting the starting point and the ending point • SI Unit – meters • Other options- km, mi, cm

  6. Displacement • Distance with a direction • Distance – 5 kilometers • Displacement – 5 Kilometers North • How much an object is displaced • When objects travel in a straight line the magnitude (amount) of the displacement is equal to the distance travelled • When an object does not travel in a straight line, distance and displacement will be different

  7. Vectors • Vector Quantities • Have magnitude and direction • Scalar Quantities • Only have magnitude • Vector quantities can be represented with arrows of a scaled length • Length shows magnitude • Arrow shows direction 3 km 3 km 3 km + 3 km = 6 km

  8. Vectors & Scalars

  9. Displacement in a straight line 4 km 7 km 4 km + 7 km = 11 km 8 km • 5 km 8 km - 5 km = 3 km

  10. Displacement that isn’t on a straight Path • Resultant Vector (red) – vector sum of 2 or more vectors 3 km 5 km 2 km Finding Distance Using Scalar Addition 1+1+2+3 = 7 km Finding Displacement using Vector Addition = 5 km NE 1 km 1 km

  11. These two vectors have the same ________________ and opposite ________________.

  12. These two vectors have different ________________ but the same ________________.

  13. These two vectors have the same ________________ AND the same ________________.

  14. average Speed • Average Speed is equal to distance divided by time • How fast or slow something is going • A rate of motion

  15. Instantaneous Speed • Speed at a given moment of time • What the speedometer on a car reads

  16. Constant Speed • When speed is not changing • Instantaneous speed is equal to average speed at all times • NOT Speeding up or slowing down • Only ways to change speed is to speed up or slow down

  17. Velocity • Speed AND direction that an object is moving • Vector Quantity • + or – sign indicates which direction the velocity is • + means North, Up, East, or to the Right • - means South, Down, West, or to the left • Sometimes multiple velocities can affect an objects motion • Sailboat, airplanes • These velocities combine with Vector Addition

  18. Speed vs. Velocity • Speed – tells how fast something is moving • Ex. 100 km/hr • Velocity – tells how fast something is moving and its direction • Ex. 35 mph North • Can an object move with constant speed but have a changing velocity? • Can an object move with constant velocity but have a changing speed?

  19. acceleration • Acceleration – The rate at which velocity changes • Can be described as …. • Changes in Speed • Changes in Direction • OR change in both Speed and Direction • Vector Quantity • Units are meters per second per second or m/s2

  20. Can an object moving with constant speed be accelerating?

  21. Devices in Cars that lead to acceleration

  22. Calculating Acceleration • Divide the change in velocity by total time

  23. Example • A car starts from rest and increases its speed to 25 m/s over the course of 10 seconds. What is the car’s acceleration?

  24. Graphs of motion • Motion can also be depicted very well using graphs • Two types of graphs • Displacement vs. time (D-t) graphs • Velocity vs. time (V-t) graphs Straight,upward line on a V-t graph means constant acceleration Straight,upward line on D-t graph means constant velocity Displacement (m)

  25. D-t graph of constant ‘v’ • Displacement increases at regular intervals, so constant velocity • Graph below Increases displacement by 5 meters every sec. • To find vel. on a disp.- time graph, find Slope

  26. Slope • Tells the rate of increase of the y-value as you move across the x values for any graph • Slope = rise / run • In other words… how much the graph goes up divided by how much the graph goes across • Slope tells us properties of the motion being depicted • On a displacement time graph  slope = velocity • On a velocity-time graph  slope = acceleration Rise/run=slope= 25/5 = 5 m/s Rise = 25 If you took slope of smaller sections of the graph you would get the same answer since ‘v’ is constant Run = 5

  27. Velocity- Time graphs • v v. t graphs may look the same as some D v. t graphs, but the motion they describe can be very different because they deal with velocity, not distance. • **The slope, of a Velocity v. Time graph indicates Acceleration**.

  28. Distance-time graph of changing velocity What is v for 0-1 sec.?? What is v for 0-2 sec.?? What is v for 3-5 sec.?? What is v for 0-5 sec. ??

  29. Distance-time graph of constant acceleration • Parabola….. If + acc, line keeps getting steeper and steeper d t

  30. Avg. velocity from 0-1 sec. ? 4 m/s • Avg. vel. From 3-4 sec? 16.5 • Acc. From 2-3 sec? 7 m/s2

  31. Velocity vs. Time graph of constant acceleration Velocity (m/s)

  32. Speed-time graph • Slope = rise/run … • Rise = • 16 • Run = • 4 • Rise/run = • 4 m/s = acceleration • Position –time Graph • Slope = rise/run … • Rise = • 50 • Run = • 5 • Rise/run = • 10 m/s = speed

  33. Free Fall Acceleration • As objects fall toward the Earth they are accelerating at a rate of 9.8 m/s2 downward • We can usually round 9.8 m/s2 to 10 m/s2 • Objects in free fall will gain 10 m/s of speed for every 1 second it is falling

  34. Free Fall Acceleration • Object is in free-fall any time it is ONLY under the influence of gravity • Including when something is thrown upwards • All objects (regardless of mass) fall at the same rate on Earth, when air resistance is ignored Ball thrown upward with initial velocity of +30 m/s

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