1. FORCE, MOTION AND ENERGY
TODAY’S OUTCOMES:
FORCE, MOTION AND ENERGY
- Review the concepts of speed and average speed
- Determine what is required to make a moving object change direction
- Learn how to represent different types of motion with graphs

2. Average speed = total distance / total time = 75 miles / 90 minutes
8. Ann and Beth went to the airport. Ann stopped for lunch, and Beth didn't. Here is a graph of their trips.
How did their average speeds compare?
Was Ann’s average speed greater than, the same as,
or less than Beth’s?
Because both drivers traveled the same distance in the same total time, their average speeds were the same.
9. As you can tell from the graph, Ann drove the first 40 miles at 60 mph, and then stopped
for lunch, which took 20 minutes. But now she was going to be late, so she drove the rest of the way
(35 miles) at 70 mph. What was her average speed for the trip?
Average speed = total distance / total time
= 75 miles / 90 minutes
= miles/minute = 50 miles/hour
Averaging the two numbers is not the correct way to do this!

3. Average speed must account for the stopped time, and for the different AMOUNTS of time spent at each speed.
On a distance vs. time plot, a steeper slope describes a higher speed.
Ann goes the same speed the whole time - how does her average speed compare to her speed at any moment in the trip?
Ann’s average speed equals her speed at any instant on the trip, because her speed was CONSTANT.
Except for when she stopped, how does Beth’s speed during the trip compare to her average speed?
Beth’s average speed was lower than her actual speed while she was moving, because her stop time lowered the average.

4. What is the average speed here?40
Straight line means
constant speed 30
What is the average speed
here?
distance (miles) 20
40 miles/hour 10
What is the speed
at 10 minutes?
40 miles/hour 10 20 30 40 50 60
at 30 minutes?
time (minutes)
40 miles/hour
at 45 minutes?
40 miles/hour
Average speed = speed only if the speed is constant.
In your plots for the rolling balls, was the speed constant?

5. What if you have a totally 40
YES - it is 40 miles/hour
What if you have a totally
non-constant speed? Can you still find average speed? 30
distance (miles) 20 10 10 20 30 40 50 60
time (minutes)
Average speed over an interval depends only
on the start position and time, and the end position and time.
Average speed is the slope of the line connecting the start and end points on a distance vs. time plot.

6. WHAT YOU ARE EXPECTED TO KNOW:
- How to determine average speed from distance and time data
- How to plot and interpret distance vs. time data
WHAT YOU ARE EXPECTED TO KNOW:

7. FORCE, MOTION AND ENERGY
TODAY’S OUTCOMES:
FORCE, MOTION AND ENERGY
- Review the concepts of speed and average speed✓
- Determine what is required to make a moving object change direction
- Learn how to represent different types of motion with graphs