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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 • 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 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 Relative Motion Or a more recent example 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 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 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 Vectors & Scalars VectorsHave Magnitude & Direction ScalarsHave only Magnitude Examples Examples Displacement Distance Velocity Speed Acceleration Mass Force Time 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 Displacement that isn’t on a straight Path 3 km • Resultant Vector (red) – vector sum of 2 or more vectors 1 km 2 km 1 km Finding Distance Using Scalar Addition 1+1+2+3 = 7 km Finding Displacement using Vector Addition = 5 km NE • These two vectors have the same ________________ and opposite ________________. • These two vectors have different ________________ but the same ________________. • These two vectors have the same ________________ AND the same ________________. average Speed • Average Speed is equal to distance divided by time • = • How fast or slow something is going • A rate of motion Instantaneous Speed • Speed at a given moment of time • What the speedometer on a car reads 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 Average Speed Constant Speed Instantaneous Speed The Average speed over some time Maintaining the same Speed of an object at a speed all the time particular moment in time 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 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? 2 ways to change Speed Speed Up Slow Down 3 ways to change Velocity Speed Up Slow Down Change Direction 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 3 Way to Accelerate Speed Up Slow Down Change Direction Can an object moving with constant speed be accelerating? Devices in Cars that lead to acceleration Calculating Acceleration ℎ ∆ − • = = = •Divide the change in velocity by total time 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? •= •= − (25 = − 10 0) 0 = m 2.5 2 = 25 = 10 = − = (32 = = − 10 ) = 7.33 m 3 2 = Graphs of motion • Motion can also be depicted very well using graphs • Two types of graphs Displacement (m) • Displacement vs. time (D-t) graphs • Velocity vs. time (V-t) graphs Straight,upward line on D-t graph means constant velocity Straight,upward line on a V-t graph means constant acceleration 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 30 ( d 25 i s 20 p l t 15 a c m10 e m 5 e 0 n ) 0 1 2 3 time (s) 4 5 6 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 30 Rise/run=slope= 25/5 = 5 m/s ( d i 25 s p 20 l 15 a m c 10 e m 5 e n 0 t ) Rise = 25 0 1 time (s) 2 3 Run = 5 4 5 6 If you took slope of smaller sections of the graph you would get the same answer since ‘v’ is constant The slope of ______________ lines indicates ______________. When tangent lines become ______________ with time, this means that the object is ______________ up. (It was originally at ______________.) The object is moving ______________ from the reference point with time. The tangent lines are getting ______________ steep with time. This means that the object is ______________ down (to a ______________). Because distance is ______________ with time, the object is moving ______________ from the reference point. 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**. The object has ______________ acceleration. The object moves with _________________ velocity. What motion does this graph represent? This object is at ______________ because its velocity is always ______________. This object’s velocity is _________________ with time. This graph shows ________________ acceleration (one _____________). This object is _________________ up. Distance-time graph of changing velocity 30 25 d i 20 s t a 15 n c e 10 Displacement (m) 0 0 1 8 2 11 3 18 4 15 5 25 ( Time (s) m ) 5 0 0 1 2 3 Time (S) 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. ?? 4 5 6 Distance-time graph of constant acceleration • Parabola….. If + acc, line keeps getting steeper and steeper d t 30 V 25 e l o 20 c i 15 t y 5 ) ( 10 m / s 0 0 1 2 3 4 5 6 Time (S) • 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 Velocity vs. Time graph of constant acceleration Velocity (m/s) • 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 Free Fall Acceleration • As objects fall toward the Earth they are accelerating at a rate of 9.8 m/s2 downward 2 2 • We can usually round 9.8 m/s to 10 m/s • Objects in free fall will gain 10 m/s of speed for every 1 second it is falling Time (sec) Instantaneou Acceleration s Speed (m/s) (m/s2) 0 0 10 1 10 10 2 20 10 3 30 10 4 40 10 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 Time (sec) Instantaneou s Vel. (m/s) Acceleration (m/s2) 0 +30 -10 1 +20 -10 2 +10 -10 3 0 -10 4 -10 -10 5 -20 -10 6 -30 -10 Ball thrown upward with initial velocity of +30 m/s