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

2. Ch 2 Motion
CLE 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

3. 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

4. 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

5. 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

6. 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

8. 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?

9. 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

10. Graphing Motion

11. 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

12. 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)

13. 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) = m/s2 2 s

14. 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

15. 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

16. Forces