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# Keynote; ch. 9; speed & accelerations

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Ch. 9 notes, physics, speed, velocity, acceleration, energy

Ch. 9 notes, physics, speed, velocity, acceleration, energy

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### Transcript

• 1. Science Notes: Ch. 9; Motion & Energy
• 2. Science Notes: Ch. 9; Motion & Energy
• 3. Position & Motion An object’s position is defined by a reference point and a reference direction. A reference point is something used for comparison to determine if an object is in motion. An object is in motion If the object changes position relative to a reference point.
• 4. Reference Point
• 5. Distance Distance is the length of a path between two points.
• 6. Displacement Displacement is the length and direction an object has moved from its starting point. Don’t confuse distance with Displacement.
• 7. Speed An object’s speed is the distance it travels in a given amount of time. Equation; Speed = distance/time S = d/t
• 8. Practice problems... Click for constant speed Word Problems...
• 9. Average speed Equation In most real-world situations, speed is not constant but changes, requiring several calculations. Average speed = Total distance/Total time. Average S = total d/total t Sa = Dt /Tt Dt = 32km + 13km = 45km T t = 2hr + 1hr = 3hr Sa = 45km/3hr, = 15km/hr
• 10. Instantaneous Speed The speed at which an object is moving at a particular point in time.
• 11. Graphing speed Constant speeda... Increasing speeda...
• 12. Slope... The slope of a d vs. t (d-t) graph is the rise over the run (y over x). Active art Here The slope of a d-t graph represents the speed.
• 13. Graphing speed, cont... Reducing speeda Final speeda
• 14. More d-t graphs...
• 15. Which graphs are impossible?
• 16. Vectors A Vector is a quantity that has both a magnitude and a direction. Example: 45 mph Northwest.
• 17. Velocity Velocity and speed are different! Velocity is speed in a given direction. IMPORTANT; Changes in velocity may be due to change in speed, change in direction, or both!!
• 18. Velocity equation Velocity is change in speed or direction so... Initial speed minus final speed... V = S1 - S 2 = meters/sec = change in m/s. If S1 - S2 is positive its speeding up. If S1 - S2 is negative its slowing down. A velocity always has a direction with it: “3m/s in a N-W direction”
• 19. D-T graphs, slope, & velocity...
• 20. Acceleration... Change in speed or direction is called acceleration. Increase in speed is acceleration, decrease in speed is deceleration. ***An object can still be accelerating even if its speed is constant if it changes direction. For example the seats in a Ferris wheel are accelerating even though the speed may be constant because they are moving in
• 21. Here’s what acceleration looks like...
• 22. Acceleration equation... So... acceleration is change in velocity per unit of time. Here’s the formula... A = V1 - V 2 = meters/sec = m/s 2 T 1 - T2 sec V1 is the initial velocity and V2 is the final. and...
• 23. Acceleration equation... T1 - T2 is the total elapsed time... T1 - T2 is always positive (can’t go back in time if V1 - V2 is positive the object is accelerating if V1 - V2 is negative the object is decelerating. (note this is not how the book presents it...
• 24. Graphing Acceleration If there is a curved line on a d-t graph the object is either accelerating or decelerating. Smile = accelerating Frown = decelerating
• 25. This is acceleration on a d-t graph Smile up = accelerating, smile down decelerating.
• 26. This is acceleration
• 27. Graphing Acceleration on a v-t graph A sloped line (either positive or negative) on a v-t graph represents acceleration.
• 28. Equation for graphing acceleration on a V-T graph... Only sloped portion is accelerating
• 29. V-T versus D-T graphs D-T Graph... V-T Graph... slope = velocity Straight slope = accel.
• 30. Speed vs. time graph... On an s-t graph, acceleration is always present when there is a sloped line (the graph below shows constant acceleration not deceleration).
• 31. Acceleration is also... Related to mass and force (Einstein)(Ch. 10) Force equals mass X acceleration: F = (m)X(a) So... Acceleration equals Force/Mass: A = (f)/(m)