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What words can you think of to describe the motion of an object?<br />
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VELOCITY<br />The word scientists use to describe how fast an object is moving in a certain direction.<br />
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Velocity is measured as:<br />a change in distance per change in time<br />change in distance<br />change in time<br />What are some things you can think of that are measured like this?<br />
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What are some examples of objects that move at high velocities?<br />220 mph<br />1600 mph<br />
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What are some examples of lowvelocities?<br />50 yds/hr (.03 mph)<br />1.2 mph<br />
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What units would you use to measure the velocity of an object moving in this classroom?<br />meters per second<br />m<br />s<br />Meters per second tells us how many meters something can move in one second.<br />
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Converting Velocities<br />1 highway, 0 city<br />1 hwy, 0 city<br />m/s into km/hr<br />m<br />s<br />“What kind of mileage does this get?”<br />1000 m/km<br />3600 seconds/hr<br />Just take the m/s multiply by 1000 and divide by 3600<br />
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What else can we know about an object’s motion besides velocity?<br /><ul><li>What if the object speeds up?</li></ul>What if the object slows down?<br />What if the object’s velocity changes?<br />
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Scientists have a special way to measure a change in velocity:<br />Acceleration<br />Acceleration is a change in velocity.<br />
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Visualizing Acceleration<br />Here you can see how the ball travels a further and further distance each second.<br />That is because its velocity is continuing to increase.<br />
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If you’re speeding up, you have positive acceleration.<br />If you’re slowing down, you have negative acceleration.<br />
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Example:<br />You’re driving along in your car and suddenly have to slam on your brakes for a red light. <br />Negative or positive acceleration? <br />High or low acceleration?<br />
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Example:<br />You’re an astronaut waiting in your shuttle for takeoff. Suddenly the rockets fire and you’re on your way. <br />High or low positive or negative acceleration?<br />
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Answer <br />High positive acceleration because you’re speeding up quickly.<br />
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Example:<br />You’re driving down the highway when your car runs out of gas and you slowly roll to a stop on the side of the road.<br />
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Answer <br />Low negative acceleration because you’re slowing down slowly.<br />
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Example:<br />You are at cruising speed on the highway. You no longer feel any pressure against the seat or are lurching forward.<br />What is your acceleration?<br />
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Answer <br />Zero, because you are at constant velocity<br />That velocity can be fast, slow, or not moving at all.<br />
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Challenge Question:<br />You throw a basketball up in the air. It rises to a certain height and then falls back to earth.<br />Describe its acceleration<br />Hint: There are multiple steps<br />
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Answer <br />First, high positive acceleration because it speeds up quickly as it leaves your hand.<br />
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Answer <br />Then, as it rises, low negative acceleration, because it begins to slow down slowly because of gravity.<br />
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Answer <br />At the top of the arch, it has zero acceleration, because it briefly stops moving upward and has constant velocity.<br />
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Answer <br />As it begins to fall again, low positive acceleration, because it speeds up slowly.<br />
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Answer <br />Finally, when you catch it, high negative acceleration because it slows down very quickly in your hand.<br />
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How Do I Graph the Motion of a Particle?<br />
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Car 1 is moving with a velocity of 1 m / sec<br />There is zero acceleration<br />
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Car 2 has constant velocity throughout at 1 m /sec<br />Its acceleration remains zero<br />
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Car 3 has a changing velocity throughout, finishing at 7 m / sec<br />Acceleration is 1 m / sec2<br />
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Quick Review<br />Velocity: speed of motion in a direction<br />Acceleration: change in velocity<br />What causes an object’s velocity to change?<br />
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If you’re riding your bike and want to speed up, what do you do?<br /><ul><li> If you’re driving a car and want to slow down, what do you do?
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If you’re playing soccer and want to move the ball, what do you do?</li></li></ul><li>Nothing will change speed unless acted upon by a force.<br />If it’s sitting still, it will keep sitting still. If it’s moving fast, it will keep moving fast. <br />
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Only a force can change the velocity of an object.<br />That force can act to accelerate it<br />NSF North Mississippi GK-8<br />
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Only a force can change the velocity of an object.<br />That force can act to decelerate it<br />
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Then why do things slow down?<br />Flying balls slow down and eventually stop because of the force of gravity.<br />Cars and bikes eventually slow down and stop because of the force of friction.<br />
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Then why do things slow down?<br />In space with no friction and no gravity, objects will keep going at the same speed forever without a force to slow them down or speed them up.<br />
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