Ch 2 Motion Bellwork: Distance Acceleration Displacement Force Speed Net Force Average Speed Balanced Force Instantaneous Speed Inertia Velocity

Ch 2 Motion CLE 3202.3.1 Investigate the relationships among speed, position, time, velocity, and acceleration I CAN: Distinguish between distance and displacement I CAN: Explain the difference between speed and velocity I CAN: Interpret motion graphs

Sec 1: Describing Motion Motion occurs when an object changes its position relative to a reference point. Motion of an object is dependent upon the reference point chosen. Frame of reference – coordinate system in which the position of the objects is measured X and y axis on a graph Mail truck at first house Mail truck at last house Mail truck moved because position relative to the street Reference point – tree, mailbox, house, parked car, car driving down the street

Sec 1: Describing Motion Distance – how far an object moves; SI unit of distance or length is centimeter (cm), meter (m) or kilometer (km) Displacement – distance and direction of an object’s change in position from starting point Distance and displacement would be the same if the object only moves in one direction. 50 yard dash – distance and displacement same Runner jogs to 50m mark and then turns around and runs back to 20m mark. 50m original direction, 30m in opposite direction Total distance ran is 80m Total distance from starting line is 20m

How do distance and displacement differ? Distance – how far an object has moved Displacement – includes distance and direction of an objects change in position from starting point

Speed Speed – distance an object travels per unit time; how fast an object is moving Rate – any change over time Speed – rate at which distance is traveled or rate of change in position Speed (m/s) = distance (meters) time (seconds) Km/hour – car on highway Km/sec – rocket escaping Earth’s atmosphere Cm/yr – geologic plate movements

Calculating Speed Average speed – speed of motion when speed is changing; total distance traveled divided by total time of travel Instantaneous speed – speed at a given point in time Speedometer – how fast a car is going at that instant – at one specific point in time Speed up/slow down – instantaneous speed changes constantly Constant speed – instantaneous speed doesn’t change – same at every point in time Examples of when instantaneous speed might change?

Calculating Speed Motion with Constant Speed – highway driving; can measure speed over any interval Changing Speed – usually speed is not constant; speed up and slow down How would you describe speed of an object when speed is changing? Average speed over entire motion or instantaneous speed at a given time

Graphing Motion

Calculating Speed Velocity – speed of an object plus direction of motion Because it has direction – velocity can change even though speed remains constant Escalators up and down – different velocities – opposite directions Race cars around a track – going in an oval means changing velocity because direction of motion is constantly changing Constant velocity – speed and direction cannot change Describe velocity of an object that travels north 6.9m in 3s, then turns and travels south 2.8 m in 4s. Velocity = 2.3m/s north then 0.7m/s south

Calculating Speed Acceleration – change in velocity; speeding up and slowing down has direction like velocity Velocity can be change in how fast something is moving or a change in direction it moves Acceleration occurs when an object changes speed, direction, or both a = Final velocity-initial velocity time traveled a = Vf – Vi/ t a = change in velocity (m/s) t (s)

Calculating Acceleration Positive Negative Jetliner takes off, reaches 80 m/s in 20s Speeding up a = (80 m/s – 0 m/s) = 4 m/s2 20s Skateboarder moving at constant speed of 3 m/s in straight line, stops in 2s Slowing down a = (0 m/s – 3 m/s) = - 1.5 m/s2 2 s

Calculations A ball is dropped from a cliff and has an acceleration of 9.8 m/s2. How long will it take the ball to reach a speed of 24.5 ms? 9.8 m/s2 = (24.5 m/s – 0 m/s) = t 24.5 m/s2 = 2.5 m/s 9.8 m/s2 A sprinter leaves the starting blocks with an acceleration of 4.5 m/s2. What is the sprinter’s speed 2 s later? 4.5 m/s2 = (X – 0 m/s) = 9.0 m/s 2s

Motion and Forces Force – a push or a pull Net Force – when two or more forces act on an object at the same time, forces combine Balanced Force – net force is zero because two forces cancel each other Inertia – tendency of an object at rest to resist any change in its motion

Forces