1. Chapter 2
Motion and Speed

2. Section 1 Describing Motion
Distance- how far an object has moved
Displacement- DISTANCE AND DIRECTION of an object’s change of position from a starting point
How do distance and displacement differ?

3. Describing Motion-cont.
Speed
Rate- any change over time
Speed=distance/time
constant speed doesn’t change over time
objects usually have a changing speed
instantaneous speed-speed at any given point in time
What are two examples of motion in which the instantaneous speed changes?

4. Describing Motion-cont.
A distance-time graph displays motion of an object over time.
Plot distance an a vertical axis
Plot time on a horizontal
What was the average speed of each swimmer over the 30-min period?

5. Describing Motion-cont.
Velocity-SPEED and DIRECTION of an object’s motion
Motion of Earth’s crust—so slow we don’t notice
How are velocity and speed different?
How do the continents drift?

6. Section 2 Acceleration Acceleration-change in velocity’s rate
Positive acceleration-speed is___________
Negative acceleration-speed is ___________
When an object changes speed or direction, it is accelerating

7. Acceleration-cont. Calculating acceleration
acceleration=change in velocity/time
change in velocity=final velocity-initial velocity
unit for acceleration=meters per second squared
positive acceleration= +# with a + slope on a velocity-time graph
negative acceleration= -# with a –slope on a velocity-time graph

8. Acceleration-cont. Amusement park acceleration-roller coasters
Changes in SPEED cause acceleration.
Changes in DIRECTION cause acceleration.
What material are roller coasters with the steepest hills made from?

9. Section 3 Motion and Forces
Force- a push or pull that one body applies to another
A force can cause an object’s ______ to change,
When two or more forces combine at the same time, they create a net force.
balanced forces are equal in size and opposite in direction
unbalanced forces are unequal in size and / or are not in the same direction

10. Motion and Forces-cont.
Inertia and Mass
Inertia- an object’s resistance to any change in motion.
Objects with greater _____ have greater inertia.
Newton’s first law of motion- an object’s moving at a constant velocity keeps moving at that velocity unless a net force acts on it; an object at rest will stay at rest unless a net force acts on it.

11. Motion and Forces-cont.
Auto crashes-the law of _________ at work.
A passenger not wearing a seat belt keeps moving ________ at the car’s speed even after the car stops.
A passenger wearing a seat belt slows down as the car slows down and stops.