Chapter 10

1. Chapter 10 Motion

2. 10.1: An object in motion changes position • You know that: • Objects can move in different ways • An object’s position can change • You will learn: • How to describe an object’s position • How to describe an object’s motion

3. Position describes the location of an object • Position: • The location of a place or object • Relative to where you are or your perspective • Relative to another object (reference point) • In order to accurately discuss two locations: • You need to compare the location of the object with the location of another object or place

4. Describing a position: • Reference point: • A location to which you compare other locations • Longitude and Latitude: • Longitude describes how many degrees east or west a location is from the prime meridian • Latitude describes how many degrees north or south a location is from the equator • Graph coordinates: • The x and y coordinates on a graph are reference points.

5. Measuring distance • Standard unit of length: • Meter (m) = 3.3 feet • Straight-line distance: • Measurement of the distance between two points when connected by a straight line • Total distance or path distance: • The actual distance traveled between two points • Depends on the path you take to get from point A to point B

6. Motion is a change in position • Motion: • The change in position over time • Can be a combination of both horizontal and vertical position change • Any change in position indicates motion • Described by the object’s speed and direction of travel • Faster objects move farther than slower objects over the same amount of time

7. Relative motion • Motion that is observed from the observers point of view • How an observer sees motion when compared with his own motion • Example: • Page 317: • Depending on your point of reference, either the bus or the street sign is changing position.

8. relative motion demo

9. You know: • An object’s position is measured from a reference point • You can use distance and direction to describe the position of an object • An object in motion changes position over time • You will learn: • How to calculate an object’s speed • How to describe an object’s velocity

10. Speed: • A measure of how fast something moves or the distance it moves, in a given amount of time. • The rate at which the distance an object moves changes compared to time.

11. Calculation of speed: • You need to know both the distance and the time • Found by dividing the distance the object travels by the time it takes to cover the distance • Speed = distance ÷ time • S = d / t • Standard unit for speed is meters per second (m/s) • In the US we measure speed in miles per hour (mph) • One mile per hour = 0.45 m/s

12. Average speed • Instantaneous speed is the “moment to moment” speed • Speed is not constant • When you look at the time it takes a runner to complete 4 laps around the track, you can calculate his average speed • Total distance ÷ total time

13. Distance-Time graphs • A graph that plots the distance the object travels against time. • Show you how speed relates to both distance and time • Time is plotted on the x-axis (horizontal) • Distance is plotted on the y-axis (vertical) • To determine the speed of an object from a distance-time graph: • Change in distance ÷ change in time

14. Velocity • Velocity: • A speed in a specific direction • Vector: • A quantity that has both size and direction • Velocity is an example of a vector • Speed is NOT a vector • It only measures how FAST or SLOW an object moves—not the direction • Two objects can have the same speed but different velocities…HOW?

15. Page 326: • Each ant’s direction of motion changes with the bends in the branch • Arrows show the ant’s direction and speed (longer arrows = faster speed) • How do the velocities of each ant compare?

16. 10.3: Acceleration measures how fast velocity changes • You know that: • Speed describes how far an object travels over a given period of time • Velocity is a measure of the speed and direction of motion • You will learn: • How acceleration is related to velocity • How to calculate acceleration

17. Speed and direction change with time • Acceleration: • The rate at which velocity changes with time • A measure of how quickly the velocity is changing • If velocity does not change, there is no acceleration • Acceleration is a vector; it has both size and direction

18. Page 330 • If acceleration is in the same direction as the object is moving • The object is speeding up • Positive acceleration • If acceleration is in the opposite direction as the object is moving • The object is slowing down • Negative acceleration • If acceleration is in at a right angle to the motion • The direction of motion will change by some angle but the speed remains the same

19. Acceleration can be calculated from velocity and time • To measure acceleration, you need to know: • The change in velocity by comparing the initial velocity and the final velocity • The time interval used for the change in velocity • The car went from 0 to 60 in 4 seconds • Initial velocity • Final velocity • Time interval

20. Calculating acceleration final velocity – initial velocity • acceleration = change in time • vfinal - vinitial a = t • Standard unit for acceleration is meters per second squared or m/s2 because: • Velocity is expressed in m/s • Time is expressed in seconds

21. Acceleration can be negative: • A car traveling at 10 m/s takes 2 seconds to stop for a red light. What is the acceleration of the car? • vfinal - vinitial a = t

22. Velocity-Time graphs pg 334 • Shows you a change in acceleration • Time is plotted on the x-axis (horizontal) • Velocity is plotted on the y-axis (vertical) • A rising line • indicates positive acceleration • The steeper the line, the greater the acceleration • A flat line • Indicates no acceleration • A falling line • Indicates negative acceleration

23. graphing acceleration acceleration comparison