MOTION
SECTION 2 - VELOCITY
How fast do you think we are traveling (orbiting) around the sun? 67,0672 mph How fast do you think we are spinning around our axis as we move around the sun? 1,041.67 mph Why don t we feel this motion? Question!?!?
Frame of Reference To describe motion accurately, a frame of reference is necessary. Frame of Reference is a system of objects that are not moving with respect to one another
Frame of Reference Motion is a change in position relative to a frame of reference Relative Motion Movement in the relation to a frame of reference
Example: The speed of the passenger with respect to the ground depends on the relative directions of the passenger s and train s speeds: 16.2 m/s 13.8 m/s
Example: The Bus Ride A passenger is seated on a bus that is traveling with a velocity of 6 m/s east. If the passenger remains in her seat, what is her velocity: a) With respect to the ground? 6 m/s east b) With respect to the bus? 0 m/s c) The passenger decides to approach the driver with a velocity of 1 m/s. What is the velocity of the passenger with respect to the ground? 7 m/s east
Frame of Reference Question If you are standing in one place, and your friend walks by you: a. Are you moving relative to your friend? No b. Is your friend moving relative to you? Yes c. Are you moving relative to the earth? No d. Is your friend moving relative to the earth? e. Is either of you moving relative to the sun? Yes Both are moving
What is needed to describe motion accurately? Frame of Reference
What is Motion? Motion The displacement of an object in relation to objects considered to be stationary.
Two kinds of motion: Linear Motion Motion in a straight line. Examples: 1. Driving on a straight road 2. Bowling ball down an alley (No hook) 3. A free falling rock
Two kinds of motion: Curvilinear Motion Motion along a curved path. Examples: 1. Throwing a ball 2. Swinging pendulum 3. Roller Coaster The Beast 4. Spinning lawn-mower blade
Distance Distance The length of the path between two points. SI Units Meter (m) Kilometers (km)
Displacement Displacement The difference between the starting point and ending point with a direction. SI Units Meter (m) Kilometers (km)
Example: Distance/Displacement Example Think about the motion of a roller coaster car. Describe the distance the coaster moved. The path along which the car travelled What would the displacement be for a roller coaster? Distance from getting on the coaster to getting off the coaster (Most the time = 0)
Formula for displacement d = (d final d initial ) d is a Greek letter used to represent the words change in. d therefore means change in d
Speed Speed How fast a particle is moving Scalar quantity Change in distance over time
Equation Speed V = d / t v = speed d = distance t = time Units km/hr, mi/hr, m/s or ft/s.
Instantaneous Speed Instantaneous Speed Speed during a particular instant of time A car does not always move at the same speed. You can tell the speed of the car at any instant by looking at the car s speedometer.
Velocity In physics, velocity is speed in a given direction. When we say a car travels at 60 km/h, we are specifying its speed. When we say a car moves at 60 km/h to the north, we are specifying its velocity. A quantity such as velocity that specifies direction as well as magnitude is called a vector quantity. Speed is a scalar quantity. Velocity is a vector quantity.
Constant Velocity Constant speed means steady speed. Something with constant speed doesn t speed up or slow down. Constant velocity means both constant speed and direction. Constant direction is a straight line, so constant velocity means motion in a straight line at constant speed.
Changing Velocity If either the speed or the direction (or both) is changing, then the velocity is changing. Constant speed and constant velocity are not the same. A body may move at constant speed along a curved path but it does not move with constant velocity, because its direction is changing every instant. The car on the circular track may have a constant speed but not a constant velocity, because its direction of motion is changing every instant.
Velocity Thinker! The speedometer of a car moving northward reads 60 km/h. It passes another car that travels southward at 60 km/h. Do both cars have the same speed? Do they have the same velocity? Answer: Same speed
How is velocity different from speed? Velocity is speed with direction
Velocity Equation V = d / t Units: km/hr, mi/hr, m/s or ft/s (with direction) Velocity can be + or depending on direction. If Velocity is constant, motion of the object is uniform. If Velocity changes, motion of the object is variable.
Velocity problems can be solved three ways: 1. Mathematically 2. Graphically 3. Experimentally
2.1 Assessment Example #1 On a sunny afternoon, a deer walk 1,300 meters east to a creek for a drink. The deer then walks 500 meters west to the berry patch for dinner, before running 300 meters west when startled by a loud raccoon. a. What is the distance the deer walked? b. What is the displacement?
2.1 Assessment Example #2 Using your example in question #1, what is the deer s speed (in m/s) if the entire trip took 10 minutes?
2.1 Assessment Example #3: An automobile travels 2,500 m north along a straight road at constant velocity. The elapsed time is 2 minutes. Calculate the velocity in m/s.
2.1 Assessment Example #4: A jet liner passes over St. Louis at 625 mi/hr, heading straight towards Kansas City, which is 235 mi away. How much time elapses (in minutes) before the aircraft passes over Kansas City if it maintains a constant velocity.
2.1 Assessment Example #5: You drive in a straight line at 10 m/s for 1 km, and then you drive in a straight line at 20 m/s for another 1 km. What is your average speed?