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Describing and Measuring Motion

Learn about reference points, speed, velocity, and acceleration in the study of motion. Understand the formulas and units used to calculate speed and acceleration.

philipdclark
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Describing and Measuring Motion

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  1. Describing and Measuring Motion Section 1

  2. Reference Point • In order to observe an object in motion you must observe the object in relation to another object that appears to stay in the same place. • Common reference points: • Earth’s Surface • Buildings • Trees • Mountains

  3. Speed • Speed: the distance an object travels in one unit of time • Common units: • Time- seconds, minutes and hours. • Distance- meters, kilometers and centimeters. • Formula: Speed = Distance Time • SI unit for speed is meters per second (m/s)

  4. Try it out… • If you walk for 1.5 hours and travel 7.5 km, what is your speed? S= D T S= 7.5 km 1.5 hrs S= 5 km/h

  5. Average Speed Since objects do not travel at a constant speed the average speed is usually calculated. Formula: Average speed= Total Distance (m) Total Time (s)

  6. Try it out… • A car travels 30 km in the first 30 minutes of a trip and 20 km in the second 30 minutes, what is the average speed the car travels? Average speed = total distance total time Average speed = 50km 60min Average speed = .83 km/min

  7. Instantaneous Speed • The rate at which an object is moving at a given instant in time.

  8. Velocity • Velocity is the speed of an object in a particular direction. • The only difference from speed is that velocity includes direction. • Which of the following is an example(s) of velocity? a. 25 m/s forward c. 55 m/h south b. 1,500 km/h d. all of the above.

  9. Acceleration Section 2

  10. Acceleration • Acceleration is the rate at which velocity changes. • Acceleration is not just how much velocity changes. It is also how fast velocity changes.

  11. Acceleration • Since velocity involves both speed and direction acceleration refers to: • Increasing speed- running to catch a bus, throwing a baseball etc. • Decreasing speed- a car coming to a red light. Sometimes this is called deceleration. • Changing direction- a car changing lanes or going around a curve. • Can a car driving at constant speed be accelerating?

  12. Calculating Acceleration • Acceleration= final velocity- initial velocity Time • It is expressed in m/s/s or m/s2 • Suppose you get on your bicycle and accelerate southward at a rate of 1 m/s/s. • This means that every second, your southward velocity increased by 1m/s.

  13. Try it out… • A roller coaster rapidly picks up speed as it rolls down a slope. As it starts down the slope its speed is 4 m/s. But 3 seconds later, at the bottom of the slope, its speed is 22 m/s. What is its average acceleration?

  14. Show your work! • Acceleration = Final Velocity – Initial Velocity Time • Acceleration = 22m/s - 4 m/s 3 sec. • Acceleration = 18 m/s 3 sec. • Acceleration = 6 m/s2 • Acceleration is measured in m/s2 or m/s/s

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