1. Chapter 2—Motion and Forces Section 1: Describing Motion

2. Distance—the total path-length traveled by an object (add-up each leg of the trip)  Units: meters, feet, km, cm, inches, miles, light-years  Symbol: d  Scalar Quantity: quantity that has magnitude (size) only, no direction.

3. Example of Distance: A = 50 m B = 45 m C = 40 m A + B = 95 m

4. Displacement—the straight-line distance between two points, along with direction.  Units: SAME AS FOR DISTANCE  Symbol: x  Vector Quantity—a quantity that has both magnitude and direction.

5. Example of Displacement: A = 50 m B = 45 m C = 40 m C = 40 m, north

6. Speed—the rate at which a distance is traveled. ◦ Units: m/s, mi/hr, km/hr, cm/s, ft/min, mi/day ◦ Symbol: s ◦ Instantaneous speed: an object’s rate of travel at a particular instant in time ◦ Average Speed—the total distance traveled divided by the total time of travel. ◦ Scalar Quantity

7. Example Problem: A car travels 120 km at 60km/hr. It then turns around and returns to its starting point at 30 km/hr. What was its average speed for the entire trip? d 1 = 120 kmd 2 = 120 km s 1 = 60 km/hrs 2 = 30 km/hr t 1 = d 1 /s 1 t 2 = d 2 /s 2 t 1 = 120 km/60 km/hrt 2 = 120 km/30 km/hr t 1 = 2 hrst 2 = 4 hrs s = d tot /t tot s = 240 km/6 hrs s = 40 km/hr

8. Velocity—the rate of change in an object’s displacement ◦ Units: SAME AS FOR SPEED ◦ Symbol: v ◦ Vector Quantity ◦ Average Velocity—total displacement divided by total time of travel. v = x/t

9. Find the average velocity of the car from the previous example problem. The car’s total displacement for the entire trip is zero km, since it returns to its starting point. The total time of the trip is still 6 hours (but that doesn’t really matter, now does it?) v = x/t v = 0 km / 6 hrs v = 0 km/hr

10. Terminology Review Distance Displacement Speed Velocity Scalar Quantity Vector Quantity

11. If an object changes direction during its motion, its speed will be _______ the magnitude of its velocity. If an object does not change direction during its motion, its speed will be _______ the magnitude of its velocity. Can you explain why this is so?