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Linear Motion – Speed, Velocity, & Acceleration

Linear Motion – Speed, Velocity, & Acceleration. Chapter 3 September 6 - 12 , 2012. Displacement vs. Distance. Distance (d) is It is a Example: Displacement ( Δd ) is Δd = It is a Example: Notice that both size and magnitude are stated. Distance / Displacement Examples.

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Linear Motion – Speed, Velocity, & Acceleration

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  1. Linear Motion – Speed, Velocity, & Acceleration Chapter 3 September 6 - 12, 2012

  2. Displacement vs. Distance • Distance (d) is • It is a • Example: • Displacement (Δd) is • Δd = • It is a • Example: • Notice that both size and magnitude are stated

  3. Distance / Displacement Examples John walks from the point A to B to C. • What distance does he travel? • What is the displacement? • The boy travels from around the rectangle from point B back to point B. Calculate the distance he traveled and his displacement. • Distance = • Displacement =

  4. Speed • Speed - • In equation form: • Speed is a • Any combination of distance and time units are appropriate for measuring speed. Example units:

  5. Problem Solving Strategy Variables /Diagrams Equation(s) & Rearrangement Solve Always check units, sign (+ or -), and number to make sure it makes sense!

  6. Example Problem #1 What is the speed of a girl who runs 6 meters in 2 seconds? Variables /Diagrams Equation(s) & Rearrangement Solve Does unit, sign, and number make sense?

  7. Example Problem #2 A car travels at 45 mi/hr. How far will the car travel in 20 minutes? Variables /Diagrams Equation(s) & Rearrangement Solve Does unit, sign, and number make sense?

  8. Instantaneous Speed • Things in motion often have variations in speed. • For example, a car may travel along a street at 50 km/hr, slow to 0 km/hr at a red light, and speed up to only 30 km/hr because of traffic. (link) • You can tell the speed of the car at any instant by looking at its _________________________. • Instantaneous speed is

  9. Velocity • Velocity – • Velocity is a description of • Example: • Velocity is a _____________ quantity (requires both magnitude and direction), while speed is a _______________ quantity • In equation form:

  10. Example of Speed vs. Velocity Variables /Diagrams Equation(s) & Rearrangement Solve A student travels 11 m north and then turns around and travels 25 m south. If the total time of travel is 12 seconds, find the student’s average speed and average velocity.

  11. Constant vs. Changing Velocity • For an object to have constant velocity, it must • If either (or both) speed or direction changes, then the velocity is ________________________________. • Example: A car on a curved track may have a constant speed, but because • In the following situations, is the object moving with a constant or changing velocity? • A bicyclist travels along the strand in Hermosa Beach at 15 mph. • A bicyclist travels around an oval track at 15 mph. • A swimmer does laps in the pool at a pace of 3 meters per second.

  12. Position Time Graphs Refer to Class Handout

  13. Acceleration • When the ____________ of an object changes, the object is said to be accelerating. • In equation form: • In everyday English, the word acceleration is often used to describe a state of increasing speed. But in Physics, acceleration is much MORE than just an increase in speed! • Changes in velocity include:

  14. Examples of acceleration include: • The unit of acceleration = • Example: • Example: kilometers per hour / hour = • Note: when motion is in one direction on a straight line, velocity and speed can be used interchangeably

  15. In 2.5 seconds, a car increases its speed from 12 m/s to 18 m/s. What is its acceleration? Acceleration Example Problem #1 Variables /Diagrams Equation(s) & Rearrangement Solve Does unit, sign, and number make sense?

  16. When coming to a stop at a traffic light, a bicyclist decreases his speed from 4 m/s to 0 m/s in 2 seconds. Calculate his acceleration. Acceleration Example Problem #2 Variables /Diagrams Equation(s) & Rearrangement Solve

  17. A particular car can go from rest to 90 km/hr in 10 seconds. What is its acceleration? Acceleration Example Problem #3 Variables /Diagrams Equation(s) & Rearrangement Solve Does unit, sign, and number make sense?

  18. What is this graph telling us? Change in velocity over time = acceleration

  19. Constant Positive Velocity

  20. Constant Negative Velocity

  21. Positive Velocity and Positive Acceleration

  22. Positive Velocity and Negative Acceleration

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