1. Motion
Unit 7
Chapter 5.1

2. What’s Your Position?
What is your position in the class in reference to the front board? Describe your position using cardinal directions.

3. Motion
When an object changes position over time relative to a reference point, the object is in motion.
reference point: the object that does not move
motion of objects can be described using cardinal directions … ex: N, S, E, W, SSE, up, down, etc.

4. Speed SI unit = meters per second (m/s)
def: the distance traveled by an object divided by the time taken to travel that distance.
SI unit = meters per second (m/s)
Kilometers per hour (km/h), feet per second (ft/s), and miles per hour (mi/h or mph) are also used
Speed = distance
time

5. Graph showing Speed (p. 119)

6. Calculating Speed
Suppose the time interval between the when you see a balloon pass by and the time it goes past the light post is 10 s and that the balloon traveled 50 m in that time. What is the speed of the balloon? Step 1 Write the equation for speed Speed = distance time Step 2. Put the values for time and distance into the equation and solve. Speed = distance = 50 m = 5 m/s time 10 s

7. Now you try
Find the speed of a person who swims 105 m in 70 s. Remember, the equation for speed is Speed = distance time

8. Now you try - answer
Find the speed of a person who swims 105 m in 70 s. Remember, the equation for speed is Speed = distance time speed = 105 m = 1.5 m/s 70 s

9. Do Not confuse terms speed with velocity … not the same meanings!
definition: the speed of an object in a particular direction.
Do Not confuse terms speed with velocity … not the same meanings!
Velocity must include a reference direction.
ex: “an airplane’s velocity is 600 km/h” is incorrect.
Correct = “the plane’s velocity is 600 km/h south”

10. Changing velocity
Velocity is the rate of change of an object’s position. An object’s velocity changes if either its speed or direction changes. For example, as a bus traveling at 15 m/s south speeds up to 20 m/s south, its velocity changes. If the bus continues to travel at the same speed but changes direction to travel east, its velocity changes again. And if the bus slows down at the same time that it swerves north to avoid a cat, the velocity of the bus changes, too.

11. speed changes … direction changes … both change
Acceleration
definition: the rate at which velocity changes.
Velocity changes if:
speed changes … direction changes … both change
increase in velocity = positive acceleration
decrease in velocity = negative acceleration (deceleration)
Acceleration is not only how much velocity changes but also how fast velocity changes. The faster the velocity changes, the greater the acceleration is.

12. Calculating average acceleration
final velocity – initial velocity (time it takes to change velocity)

13. Calculating average acceleration
Ex: Every second, the cyclist’s southward velocity increases by 1 m/s. His average acceleration can be calculated as follows:
Average acceleration = 5 m/s – 1 m/s = 1 m/s2
4 s

14. Recognizing acceleration on a graph (p. 122)
Acceleration can be shown on a graph of velocity versus time

15. Continuous acceleration
Even when you are completely still, you are accelerating. This is due to the earth rotating on its axis. An object traveling in a circular motion is always changing its direction. Therefore, its velocity is always changing, so it is accelerating. The acceleration that occurs in circular motion is known as centripetal acceleration. Centripetal acceleration occurs on a Ferris wheel at an amusement park or as the moon orbits Earth.

16. Centripetal acceleration
The blades of these windmills are constantly changing direction. Thus, centripetal acceleration is occurring.