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Measuring Motion

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**Words to Know speed magnitude velocity acceleration**

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**All types of motion can be described, measured, and even predicted.**

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**Rate of motion can be measured and is called speed**

Rate of motion can be measured and is called speed. Velocity is another measure of motion that takes into consideration both rate of motion (speed) and direction .

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speed = distance/time

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**velocity= distance/time in a given direction**

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**So, if speed remains constant, but direction changes, then the velocity has changed.**

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**The motion of an object can be described by its position, direction of motion, and speed.**

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**We commonly talk about travel in these terms**

We commonly talk about travel in these terms. For example, last week I left my house (starting position), went west (direction) on highway 70 at 50 km/hr (speed). I arrived at the beach (ending position) in 40 minutes.

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But we can really measure ANY motion of any object at any time by noting its position, speed, and direction.

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**In addition, we can measure changes in an object’s motion and position**

In addition, we can measure changes in an object’s motion and position. We can measure changing rates of speed (called acceleration) and we can measure changes in direction.

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**Acceleration is the measure of the change in velocity.**

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**A race car changes velocity as it goes around the track**

A race car changes velocity as it goes around the track. To calculate the acceleration of a race car, divide the change in velocity by the time it takes the velocity to change. acceleration = (final velocity - original velocity) / time or a = (v2 – v1)/t

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**We can apply the concepts of speed and velocity to enable us to measure time intervals.**

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Knowing the relationships of the velocity of planets, the moon, the earth’s rotation, etc. allow us to measure our days, months, years, etc.

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We could also measure time if we know the speed of a vehicle and the distance traveled. Since speed = distance/time, it follows that time = distance/speed

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**What is the difference between speed and velocity? **

A: only speed is distance traveled over time B: only velocity is distance traveled over time C: both are distance traveled over time but velocity takes into account direction D: both are distance traveled over time but speed takes into account direction

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**D: not enough information in the question**

A race car travels 500 km around a track in 3.5 hours. What is the speed of the car? A: 143 km/hr B: 286 km/hr C: 165 km/hr D: not enough information in the question

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**An airplane travels 500 km/hour toward the southwest for 1. 3 hours**

An airplane travels 500 km/hour toward the southwest for 1.3 hours. How far did the plane go? A: 385 hours B: 650 km C: 650 km/hr southeast D: 385 km

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**Which of the following is expressed as velocity?**

A: 45 km/hr B: 45 km/hr southwest C: 45 km south D: 45 hours

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**Which of the following is NOT a way to measure time intervals?**

A: keeping track of the movement of the moon B: knowing the speed of a vehicle and how far it traveled C: determining velocity from distance and time D: using a computerized stopwatch

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**A race car's beginning velocity is 0 km/sec**

A race car's beginning velocity is 0 km/sec. It's velocity at the end of the first lap is 0.06 km/sec. It takes 65 seconds to make the first lap. What is the race car's acceleration? A: 9.23 km/s B: 9.23 km/s/s C: 39 km/s/s D: 39 sec

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A storm becomes a hurricane as it is traveling at 17mph toward the northwest. It covers 1400 miles before being downgraded to a tropical storm. How long was the hurricane active? A: 82 hours B: 8 days C: 23,800 hours D: 14 days

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**A train travels 2500 km in 17 hours. What is the train's average speed?**

A: 425 km/hr B: 147 km/hr C: 42.5 km/hr D: none of the above

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**A: the car was traveling at 33 mph **

As you are traveling down main street at 30 mph, a car passes you going in the same direction. What can you tell about the car that passed you A: the car was traveling at 33 mph B: the car passing you was going more than 30 mph C: the car passing you was accelerating at a rate of 5 mph/h D: nothing - there is not enough information

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**A: they will meet after traveling 30 minutes **

A speed boat is traveling at 65 mph south. Another is traveling at 65 mph west. What can you tell about the boats? A: they will meet after traveling 30 minutes B: they have the same speed but not the same velocity C: they have the same velocity but not the same speed D: they have the same acceleration and the same velocity

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