1. CH. 2 Notes
Abbreviated

2. Distance vs. Displacement
Distance – the length an object travels (meters)
Displacement – straight line path between two points. (must have a direction)

3. Speed Speed is the distance an object travels per unit time.
55 mph or 10 m/s
Metric (SI) unit is meters/second
Calculating speed:

4. Distance-Time graphs Distance – Always y-axis Time – Always x-axis
Slope of the line = speed
Δy / Δx = slope
Horizontal line = no motion
Steep line = greater speed

5. Velocity Velocity is speed with a direction
Ex. 55 mph North
Because velocity depends on direction as well as speed, the velocity of an object can change even if the speed of the object remains constant.
The speed of this car might be constant, but its velocity is not constant because the direction of motion is always changing.

6. Acceleration
Acceleration is the rate of change of velocity. When the velocity of an object changes, the object is accelerating.
A change in velocity can be either a change in how fast something is moving, or a change in the direction it is moving.
Acceleration occurs when an object changes its speed, its direction, or both.

7. Speeding Up and Slowing Down
If the acceleration is in the same direction as the velocity, the speed increases. Acceleration is positive.
If the speed decreases, the acceleration is in the opposite direction from the velocity, and the acceleration is negative.

8. Changing Direction
Any time a moving object changes direction, its velocity changes and it is accelerating.

9. Calculating acceleration

10. Practice
A runner covers the last straight stretch of a race in 4 s. During that time, he speeds up from 5 m/s to 9 m/s. What is the runner’s acceleration in this part of the race? a= 9m/s – 5 m/s 4s a= 1m/s/s or 1 m/s2

11. speed-time graphs graph shows acceleration
positive slope (going up) = increasing acceleration
negative slope (going down) = decreasing acceleration
0 = no motion
horizontal line = constant speed (velocity)