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Motion

Motion. Chapter 11. What is motion?. It’s an object that has a direction It also tells how fast the object is going It also tells a location at a given time. Puttin ’ a frame on it. To describe motion accurately, a frame of reference is needed.

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Motion

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  1. Motion Chapter 11

  2. What is motion? • It’s an object that has a direction • It also tells how fast the object is going • It also tells a location at a given time.

  3. Puttin’ a frame on it • To describe motion accurately, a frame of reference is needed. • A frame of reference is a system of objects that are not moving with respect to one another. • So who is really moving? • All depends on your frame of reference.

  4. How fast you moving? • How fast are the passengers of the train moving? • There are actually many correct answers because movement is relative. • Relative motion: Movement in relation to a frame of reference.

  5. So what frame do I go with? • Once again, it all depends on what you want to know. • What would you choose if you are sitting in a bus and want to know how fast you are going relative to the ground? • What about if you walk to the back of the bus? • Know what your looking for and find a reference.

  6. We’re going the distance • Distance: Length between two points. • Always good to express distances in units that are best suited to what you want to know. • SI unit for distance is meters • Long distances are measured in Kilometers (1000 m) • Medium distances are Meters • Short distances are Centimeters (100 cm in a m)

  7. Displacements • Displacement: Direction from the starting point and the length of a straight line from the starting point to the ending point. • Typically used when giving directions. • Why?

  8. What’s your Vector, Victor? • Displacement is a vector • Vector: a quantity that has magnitude and direction. • Magnitude: can be size, length, or amount. • Arrows on a graph/map are used to represent vectors • The length of the arrow shows the magnitude

  9. Displacement in a line • When two displacements have the same direction, you can add their magnitudes. • Example

  10. What if it isn’t a straight line? • When two (+) displacement vectors have different directions, they may be combined by graphing. • Example • The vector I drew in red is the RESULTANT VECTOR: The sum of two or more vectors.

  11. Speed • Speed: Ratio of the distance an object moves to the amount of time the object moves. • SI Unit: Meters per second (m/s) • Just like before, need to use logical units.

  12. 1st Type of Speed • Average Speed: How fast something moves for the duration of a trip. • There is a formula to help figure this out: • v= d/t • v= average speed • d= total distance • t= total time

  13. Problem 1 • While traveling on vacation, you measure the times and distances traveled. You travel 35 kilometers in 0.4 hours, followed by 53 kilometers in 0.6 hours. What is your average speed? • What do you have? • What are you answering?

  14. Problem 2: Manipulate the formula • How far does a jogger run in 2 hours (7200 seconds) if his average speed is 6 m/s? • What do you have? • What are you answering?

  15. Problem 3: Manipulate for distance • How long does it take a swimmer to complete a 100 meter swim if his average speed is 10 m/s? • What do you have? • What are you answering?

  16. 2nd type of speed • Instantaneous speed: Tells you how fast you are going at a particular moment • Speedometer can measure this

  17. Graphing Speed • Also called a distance-time graph • The slope of the line is the speed • Remember Slope is figured by Rise/Run • Distance is on Y-axis • Time is on X-axis

  18. Velocity • Velocity: The speed and direction in which an object is moving • Velocity describes both speed and direction, thus making it a vector • Just like with our displacement vectors, velocity vectors uses arrows of different lengths. • Longer= Faster velocity Shorter= Slower Velocity

  19. Combining Velocities • Two or more velocities add by vector addition • Example 1: Same Direction Velocities • Example 2: Different Direction Velocities • In order to get the angle we need to use the Pythagorean theorem: • a2 + b2 = c2 • C is the hypotenuse, this is the part we want to find

  20. Acceleration • Acceleration: The rate at which velocity changes • Acceleration can be a change in speed, direction, or both. • It’s a vector

  21. Changes in Speed • Typically we think of acceleration as an increase in speed. • It can also be a decrease in speed or deceleration • Can be caused by positive (increase) change or a negative (decrease) change in speed • Example: A car

  22. I’m freefallin’ • Free fall: the movement of an object toward Earth solely because of gravity • Remember: Velocity is m/s • The units for acceleration is m/s/s or m/s2 • Gravity is 9.8 m/s2 • This means that each second an object is in free fall, its velocity increases by 9.8 m/s2.

  23. Changes in Direction • You can accelerate without changing speed • Going around a curve in a car/bike or riding a carousel are both accelerating with a constant speed.

  24. Changes in Both • Example: Roller coaster • Example: Winding Road

  25. Constant Acceleration • Constant Acceleration: a steady change in velocity • Which means, the change of velocity is the same each second

  26. Calculating Acceleration • You can calculate acceleration by dividing the change in velocity by the total time • a= (vf-vi)/t • a= acceleration • vf= Final velocity • vi= initial (starting) velocity • t= time

  27. Problem • A ball rolls down a ramp, starting from rest. After 2 seconds, its velocity is 6 meters per second. What is the acceleration of the ball? • What do we know? • What are we solving?

  28. Acceleration Graphs • Also called velocity-time graphs • Y-axis is speed • X- axis is time • Slope is acceleration

  29. Constant acceleration on Graph • Constant acceleration is represented by a straight line called a linear graph. • Positive acceleration goes upwards • Negative acceleration goes downwards • A straight line on an acceleration graph represents a constant velocity

  30. Distance-Time Graphs • Accelerated motion is represented by a curved line on a distance-time graph • This is also called a non-linear graph • You can check this by calculating the slope between two points.

  31. Instantaneous Acceleration • Instantaneous acceleration is how fast a velocity is changing at a specific instant.

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