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Describing and Measuring Motion

Describing and Measuring Motion. Lesson 1, Chapter 1 – Motion. Describing Motion. An object is in motion if its distance from another object is changing.

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Describing and Measuring Motion

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  1. Describing and Measuring Motion Lesson 1, Chapter 1 – Motion

  2. Describing Motion • An object is in motion if its distance from another object is changing. • To decide if you are moving, you use your chair as a reference point. A reference point is a place or object used for comparison to determine if something is in motion. An object is in motion if it changes position relative to a reference point. • Objects that we call stationary – such as a tree, a sign, or a building – make good reference points.

  3. Whether or not an object is in motion depends on the reference point you choose. • Are you moving as you read your book? When your chair is used as a reference point you are not. But if you choose another reference point, you may be moving. • If you chose the sun as a reference point you would be moving because you and your chair are on Earth, which moves around the sun. This is known as relative motion.

  4. Measuring Distance • Scientists all over the world use the same system of measurement so they can communicate clearly. This system of measurement is known as the International System of Units of (SI). • When describing motion, scientists use SI units to describe the distance an object moves. • The SI unit of length is the meter (m). A Meter is a little longer than a yard. • The length of an object shorter than a meter is known as a centimeter (cm) • Scientists also use the SI units to describe quantities other than length.

  5. Calculating Speed • If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object. • The speed of an object is the distance the object travels per unit of time. • Speed = Distance __________ Time

  6. Average Speed • The speed of most moving objects is not constant. • The calculate the average speed, divide the total distance traveled by the total time.

  7. Instantaneous Speed • Calculating the average speed is important, but it is also useful to know the instantaneous speed. • This is the rate at which an object is moving at a given instant in time.

  8. Velocity • Knowing the speed at which something travels does not tell you everything about its motion. To describe an object in motion you need to know the direction of the motion. • When you know both the speed and the direction of an object in motion, you know the velocity of the object. • Speed in a given direction is velocity. • You know the velocity of a storm when it is moving 25 km/h eastward.

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