section(1:((measuring(motion( - upper st. clair school ... ·...
TRANSCRIPT
¡ Observing Motion by Using a Reference Point
§ Motion is an object’s change in position relative to another object, or reference point. The object that appears to stay in place is called a reference point.
¡ The direction of an object’s motion can be described with a reference direction such as: § North § East § South § West § Up § Down
¡ Common Reference points: ¡ The Earth’s Surface is a common reference point for determining motion. § What type of motion do we measure with Earth as a reference point?
¡ Speed is the distance traveled by an object divided by the time taken to travel that distance.
¡ The SI (International Standard) unit for speed is meters per second. (m/s)
¡ Kilometers per hour (km/h), feet per second (ft/s), and miles per hour (mi/h) are other units commonly used to express speed.
¡ Determining Average Speed: Average speed equals total distance divided by total time.
¡ Average speed = total distance total time
¡ Recognizing Speed on a Graph: Speed can be shown on a graph of distance versus time.
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Distance (km)
Time (h)
¡ Velocity: Direction Matters § The speed of an object in particular direction is called velocity.
*** Speed and Velocity are two different terms with different meanings.
¡ Changing Velocity You can think of velocity as the rate of change of an object’s position. An object’s velocity is constant only if its speed and direction don’t change.
¡ Combining Velocities You can combine different velocities to find the resultant velocity.
¡ Use the diagram in your book on page 7:
Acceleration ¡ The rate at which velocity changes over time is called acceleration. An object accelerates if its speed, or direction or both change.
¡ An increase in velocity is commonly called positive acceleration. A decrease in velocity is commonly called negative acceleration or deceleration.
¡ Calculating Average Acceleration You can find average acceleration by using the equation:
Average acceleration = final velocity-‐ starting velocity time it takes to change
¡ Velocity is expressed in meters per second (m/s) and time is expressed in seconds (s). So acceleration is expressed in meters per second per second or (m/s)/s, which equals m/s2.
¡ Describe the acceleration of the cyclist on page 8 of your textbook.
¡ Recognizing Acceleration on a Graph § Acceleration can be shown on a graph of velocity versus time (refer to page 8).
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Velocity (m/s)
Time (s)