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Mechanics

Mechanics. Mechanics. In Physics, it is the study of motion …what was the study of heat? Thermodynamics What was the study of light? Optics. Mechanics. In Physics, it is the study of motion. Linear Motion…or 1D Motion…or Motion in a straight line.

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Mechanics

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  1. Mechanics

  2. Mechanics In Physics, it is the study of motion…what was the study of heat? Thermodynamics What was the study of light? Optics

  3. Mechanics In Physics, it is the study of motion

  4. Linear Motion…or 1D Motion…or Motion in a straight line

  5. Position Definition- where the object is located Positions can be positive or negative

  6. Motion needs a reference point • A reference point or reference position is needed to show if an object has moved • A reference point or reference position is needed to show how much an object has moved

  7. Motion • Motion is simply a change in position

  8. Relative Motion • http://www.aplusphysics.com/courses/honors/kinematics/honors_relative.html

  9. Relative Position *Everything moves…everything * What about the computer on the desk? * Our usual reference point is Earth, but every position is relative (compared) to the sun,stars…we are all moving compared to something else

  10. Not all motion is easy to observe • Depending on the point of reference chosen, motion may not be observable • Example –a person sitting on a bus is moving at 30 mi/h compared to a car stopped at a light (motion is easy to observe) • -- 2 people riding on a bus are not moving compared to each other (motion not easy to observe)

  11. Relative motion • When we describe motion, we describe it in relation (compare it) to the observer or a fixed point • Are the students sitting beside each other on the bus moving, compared to each other? • Compared to the person on the street?

  12. Relative motion • A person sitting on a bus throws a tennis ball upwards…what motion does the person throwing the ball see? What motion of the ball does a person waiting on the corner see?

  13. Relative Motion • All motion is relative to some fixed point or object.

  14. Review • Question: A train travels at 60 m/s to the east with respect to the ground. A businessman on the train runs at 5 m/s to the west with respect to the train. Find the velocity of the man with respect to the ground. • Answer: First determine what information you are given. Calling east the positive direction, you know the velocity of the train with respect to the ground (vTG=60 m/s). You also know the velocity of the man with respect to the train (vMT=-5 m/s). Putting these together, you can find the velocity of the man with respect to the ground.

  15. If you saw this tornado, what information from the weather man would you want?

  16. Speed Definition- a measure of how fast something is moving Formula- Speed = distance time Units- mi/h, km/h, m/s

  17. Constant Speed • Definition- a moving object that doesn’t change its speed example- school zone, long highway, jogging,

  18. What would a constant speed look like?

  19. What would no speed (an object at rest) look like?

  20. The steepness of the slope indicates how fast something is going

  21. Average Speed A more common speed would be one that the object changes as it moves… marathon runner, bird, driving a car (we have lots of stops/starts…so a lot of different speeds), getting to science class. definition- total distance total time avg speed to get to school = 0.5 miles = 31 mi .016 h h

  22. Instantaneous Speed Definition- the speed at one point in time When something is speeding up or slowing down (what is happening to its instantaneous speed?) its instantaneous speed is changing (what is happening to the instantaneous speed when its speed is constant?... doesn’t change)

  23. Review • When an athlete or ROTC student is being timed at practice….are they being timed for instantaneous speed or average speed?

  24. Graphing Motion A distance-time graph illustrates the speed of an object

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