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Motion

Learn about motion, speed, velocity, displacement, acceleration, and momentum with practical activities and sample problems to master physics concepts effortlessly.

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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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