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FORCE AND MOTION

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MEASURING MOTION

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BELLRINGERS 2. Alex rode his bicycle 60 kilometers in 4 hours. How fast was he going? Matt rode 90 meters in 6 minutes. How fast was he going? 1. What two things must you know to determine speed? What is the formula for speed? 3. Explain why is would be important to know a tornado’s velocity and not just its speed. 4. Read pg. 7 in your packet and complete the questions on the back of the page. 5. Put the finishing touches on your Car Distance/Time Graphs.

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WHAT IS MOTION? Motion is a change in an objects position over time when compared with a reference point.

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Reference point or frame of reference is the background or object that is used as comparison to the object in motion. Most common reference point is the Earth’s surface. Other reference points are buildings, trees, mountains etc. What reference point do the balloonists use?

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Motion is not absolute, it depends on the observer. For example, if Jack and Jill are sitting in a room, Jack sees Jill at rest and Jill sees Jack at rest. BUT, if we zoom out, we see that Jack and Jill are sitting on a bus moving at a constant speed of 25mph. From the reference INSIDE the bus, Jack sees Jill at rest and Jill sees Jack at rest.

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Jill’s mother, waiting for the bus, sees Jill’s bus go by at 25mph. She sees Jill traveling 25mph. Jack on the other hand, sees Jill as going 0mph. What they observe seems to depend on their reference point.

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While riding the bus, Jill begins throwing cookies to Jack. Jill can throw cookies at a speed of 30 mph. From their reference point, Jack and Jill both see the cookies going 30mph.

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As Jill’s mom observes the cookie tossing from where she is standing on the side of the road, she sees the cookies going 30mph on a bus moving 25mph in the same direction. SO, she observes the cookies going 55mph!!!!!!

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As Jill continues to throw 30mph cookies at Jack, the bus drives by Jack’s mom on a bicycle. She is riding 10mph in the same direction as the bus is traveling 25mph. From her point of reference, Jack seems to only be going 15mph (25mph – 10mph) and she see the tossed cookies going 45mph (15mph + 30mph).

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As the cookie tossing between Jack and Jill continues, a car drives by going 40mph in the other direction. The observer in the car sees Jack going 65mph (40mph + 25mph). The observer then notices the flying cookies to be traveling a whopping 95mph!!!!!! (40mph + 25mph + 30mph).

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SO WHAT IS SPEED? Speed is the rate at which an object moves. This is determined by the distance traveled and the time it takes to travel. SO… SPEED = DISTANCE / TIME UNITS FOR SPEED: meters per sec (m/s) miles per hour (mi/hr), feet per sec (ft/s)

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AVERAGE SPEED VS CONSTANT SPEED Average Speed = Total distance traveled divided by Total time of the trip

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AVERAGE SPEED VS CONSTANT SPEED Constant speed – speed that does not change. Every plot point on the graph has the same speed When you see a graph like this, you will know that the object is traveling at a constant speed. Double check yourself by calculating the speed at each point.

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SOLVE THIS PROBLEM While on vacation, Lisa traveled a total distance of 440 miles. Her trip took 8 hours. What was her average speed?

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SOLVE THIS PROBLEM While on vacation, Lisa traveled a total distance of 440 miles. Her trip took 8 hours. What was her average speed? SPEED – 55 MILES PER HOUR SPEED = DISTANCE/TIME OR SPEED = D/T DISTANCE – 440 MILES TIME – 8 HRS

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Which graph shows constant speed?

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VELOCITY Velocity is the speed of an object in a specific direction. Speed and Velocity do not mean the same thing Velocity changes as speed or direction changes.

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Which of the following are examples of velocity? 1.25 m/s forward 2.1/500 km/h 3.55 m/h south 4.10, 000 m/s X X

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BELLRINGERS 2. Alex rode his bicycle 60 kilometers in 4 hours. How fast was he going? Matt rode 90 meters in 6 minutes. How fast was he going? 1. What two things must you know to determine speed? What is the formula for speed? 3. Explain why is would be important to know a tornado’s velocity and not just its speed. 4. Read pg. 7 in your packet and complete the questions on the back of the page. 5. Put the finishing touches on your Car Distance/Time Graphs.

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COMBINING VELOCITIES 2 velocities in the SAME DIRECTION – subtract the smaller velocity from the larger velocity to find the resultant velocity. 2 velocities in DIFFERENT DIRECTIONS – add them together to find the resultant velocity.

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Acceleration is the rate at which velocity changes. SO…..if an object speeds up, slows down or changes direction, it has ACCELERATED.

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ACCELERATION – CHANGES IF SPEED, DIRECTION OR BOTH CHANGES

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TYPES OF ACCELERATION Positive Acceleration – occurs when velocity increases. Negative Acceleration – occurs when velocity decreases. This is also called deceleration.

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SO… what about this? What type of motion does it have? Is the object accelerating?

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Is the object changing speed? Is the object changing direction? YES!!!! An object traveling in a circle is constantly changing direction. SO… is the object accelerating? NO!

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Objects that are continuously accelerating is called CIRCULAR MOTION. This means that the direction is constantly changing.

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LET’S PRACTICE

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1. Consider a car moving with a constant velocity of 10m/s for 5 seconds. Look at the data table and draw a graph of the results into your notes. Does your graph look like this? What kind of graph is this? What is the speed? The object is traveling at a constant speed of 10 m/s for 5 seconds.

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2. Consider a car moving with a constant velocity of 5 m/s for 5 seconds, stopping abruptly, and then remaining at rest for 5 seconds. Graph the information into your notes. Does your graph look like this? Whenever there is a flatline, this means motion has stopped.

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3. Look at the picture and graph the information. Does your graph look like this? What is the speed? Graphs that look like this always show ……. ACCELERATION Speed is NOT the same at every point along the line

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Look at the two cars below. The blue car starts “ahead” of the red car (which actually starts off the screen). Since the red car is moving faster, it eventually catches up with and passes the blue car. Since the red car passes the blue car, there is an instant where they occupy the same position. At how many seconds and at what distance does this occur? What speed are the cars traveling at this position?

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Which car or cars are accelerating? The red car is traveling at a constant speed. Since it is constant nothing is changing!!!!! Only the blue and the green cars are accelerating. But why not the red?

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Which car is experiencing the greatest acceleration? IT MUST BE THE BLUE CAR BECAUSE IT OVERTAKES ALL THE OTHERS

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Look at the distance/time graph. Each one of the three lines corresponds to the motion of one of the three cars. Match the appropriate line to the particular color of car.

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LET’S PRACTICE

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THINK ABOUT RIDES IN AN AMUSEMENT PARK 1. WHICH RIDES HAVE CONSTANT SPEED? 2. WHICH RIDES HAVE CIRCULAR MOTION? 3. WHICH RIDES ACCELERATE?

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