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Motion

Motion. Motion. Motion is the change of an object’s position over time When we say something has moved, we are describing motion When we are describing motion, we are comparing it to a frame of reference. Motion Activity.

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Motion

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  1. Motion

  2. Motion • Motion is the change of an object’s position over time • When we say something has moved, we are describing motion • When we are describing motion, we are comparing it to a frame of reference

  3. Motion Activity • On your graph paper, draw a small picture of yourself getting ready to take a walk in the center at the top. • The center is West (Draw a dot) • You are going to walk 10 squares to the right to Mario’s for a slice of pizza • How far have you moved from West? • How far have you traveled?

  4. Motion Activity • You forgot your physical science notebook, so you have to run home 14 squares in the other direction and get it • How far have you moved from West? • How far (total squares) have you traveled?

  5. Motion Activity • You don’t want to be late for Physical Science, so you run 4 squares back to West • How far have you moved from West? • This is displacement • How far (total squares) have you traveled? • This is distance

  6. Distance vs. Displacement • Distance – the length of the path traveled between the initial and final positions of something in motion • Displacement – the shortest distance between the initial and final positions of something in motion

  7. Speed • When we talk about how fast something is traveling, we are talking about speed • Speed is the rate at which an object moves

  8. Speed • How do we calculate speed? Distance Velocity Time

  9. Speed • How do we calculate speed? Distance Speed Time

  10. Speed • Distance is usually measured in m or km • Time is usually measured in s or hr • The unit of speed is usually m/s or km/hr • Speed is used to describe anything that is changing position: • Runners, cars • Ocean currents, winds • Moon, Earth

  11. Constant Speed • Some objects have speeds that stay the same as they move • Constant speed • Speed does not change • Plot the distance vs. time for a cheetah traveling 30m/s for 5 seconds

  12. Constant Speed • A cheetah running at constant speed

  13. Constant Speed

  14. Average Speed • Some objects have speeds that change as they move • We have to calculate average speed • Speed changes over time • Think about driving in a car • Speed limit changes • Stop signs and stoplights

  15. Average Speed A car in the pick-up line at West

  16. Average Speed

  17. Average Speed • For things moving at a constant speed, the speed at any point on the line is the average speed

  18. Instantaneous Speed • For things moving at any speed, the speed at a given point in time is the instantaneous speed

  19. Velocity • Velocity is a speed in a given direction • If you drive to Raleigh, your average speed could be 97km per hr (60miles per hr) • Your velocity would be 97 km per hr east • You have to include the direction

  20. Speed and Velocity Practice • An airplane flew 1000 km in 4 hr. What is the airplane’s speed?

  21. Speed and Velocity Practice • A car travels 50 km west in 30 minutes. What is its velocity in km/hr?

  22. Speed and Velocity Practice • How long will it take a ball to roll 26m if its velocity is 2.0m/s to the right?

  23. Speed and Velocity Practice • If a runner moves with a speed of 1.5m/s and changes her speed to 2.1m/s over 3s, what is her average speed over that 3s?

  24. Speed and Velocity Practice • Work on Velocity Problems

  25. Acceleration • Think about riding a roller coaster • You go up the first hill at constant speed • After the top of the hill, your speed increases quickly • At the bottom of the hill, you slow down and make some turns and keep going • Rapid changes in velocity • The rate of change in velocity is acceleration

  26. Acceleration • Something that is speeding up, slowing down, or changing direction is accelerating • Acceleration= Final velocity-original velocity Time • What are the units of acceleration? • Acceleration tells you how fast velocity is changing

  27. Acceleration Sample Problem: What is the acceleration if we speed up from 10m/s to 30 m/s in 10 seconds? A = Vf- Vi t

  28. Acceleration Sample Problem: A roller coaster car speeds up as it goes down a hill. As it starts down the hill, its speed is 8m/s, and at the bottom of the hill 3 seconds later, its speed is 28m/s. What is its average accleration? A = Vf- Vi t

  29. Gravity • Gravity is the acceleration of an object toward Earth • g=9.8m/s2

  30. Gravity Example: Brandon drops a water balloon out a window on Dominic, who is standing below. If it takes 10 seconds for the balloon to reach Dominic’s head, what is its speed just before it hits Dominic? g = 9.8m/s2 - put in place of acceleration g = Vf- Vi What is Vi? t

  31. Momentum • Think about a football game • A 100kg fullback runs up the field and collides with an 80 kg defensive back. The 100kg fullback gets knocked to the ground by the smaller player. How does that happen? • The defensive back has more momentum • All moving objects have momentum • The more momentum a moving object has, the harder it is to stop.

  32. Momentum • If both players had the same velocity, which player would have more momentum? • What are the units for momentum? • p = m x v (p is the abbreviation for momentum) • Momentum has units of kg·m/s

  33. Momentum • Momentum depends on the mass of an object and its velocity • Momentum=Mass x Velocity • p=m x v • In the football game, how can the smaller player knock over the larger player? • His mass is smaller • His velocity must be larger

  34. Momentum • What are some things that have a large momentum? • Train – has a very large mass • Car – large mass, high speed • Harder to stop if moving faster • Stopping distance is directly related to momentum • Bullet – small mass, but high velocity

  35. Law of Conservation of Momentum • When two objects collide, one object transfers momentum to the other • The total momentum of a group of objects stays the same unless outside forces act on the objects • No momentum is lost • Total momentum is the same • Think about the football players

  36. Law of Conservation of Momentum • How do moving objects act? • Richard_Garriott_Space_Video_Blog_Conservation_of_Momentum.avi • Explains recoil of a gun http://www.batesville.k12.in.us/physics/phynet/mechanics/momentum/firing_a_gun.htm

  37. Mythbusters • Mythbusters - Lego ball • Lego Ball

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