motion is relative everything moves even though they may appear to be at rest
TRANSCRIPT
LINEAR MOTION
Motion is Relative
Everything moves even though they may appear to be at rest
Frame of Reference
Allows you to measure changes in position.
A coordinate system for specifying the precise location of an object in space
Frame of Reference
This diagram shows a change in position along the x-axis.
What about the y-axis? How do I know?
Frame of ReferencePositive and negative changes depend upon the frame of reference
Displacement
Δx = xf - xiChange in position = final position – initial position
DisplacementDoes not always equal distance traveled
Displacement
DisplacementA teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North.
Even though the teacher has walked a total distance of 12 meters, her displacement is 0 meters. During the course of her motion, she has "covered 12 meters of ground" (distance = 12 m). Yet when she is finished walking, she is not "out of place" - i.e., there is no displacement for her motion (displacement = 0 m).
Displacement ExampleThe diagram below shows the position of a cross-country skier at various
times. At each of the indicated times, the skier turns around and reverses the direction of travel. In other words, the skier moves from A to B to C to D.
Determine the resulting displacement and the distance traveled by the skier.
Displacement ExampleConsider a football coach pacing back and forth along the sidelines. The diagram
below shows several of coach's positions at various times. At each marked position, the coach makes a "U-turn" and moves in the opposite direction. In
other words, the coach moves from position A to B to C to D.
What is the coach's resulting displacement and distance of travel?
Scalar vs. Vector
Vectors
Can be represented graphically
Scalar vs. Vector Example
a. 5 m b. 30 m/sec, East c. 5 mi., North d. 20 degrees Celsius e. 256 bytes f. 4000 Calories
Determine whether the following are scalar or vector quantities.
scalarvector
scalarscalar
scalarvector
VelocityVelocity is a vector
Velocity
Velocity ExampleHeather and Matthew walk eastward with a speed of 0.98 m/s. If it takes them 34 min to walk to the store, how far have they walked?
Variables Equation Solve
v = 0.98 m/sΔt = 34 minΔd = ??
v = ΔdΔt
=v Δt Δd
Units don’t match!
34 min
1 min
60 s= 2040 s
=(0.98 m/s)(2040 s) Δd
= 1999.2 m = 2 km Δd
Instantaneous VelocityVelocity of an object at a specific point in its path
AccelerationChange in velocity over time
constant velocity
constant negative accelerationzero acceleration
constant positive acceleration
Acceleration
Acceleration is a vector!
Kinematics
Δx = vit + ½ at2
vf 2 = vi
2 + 2aΔx
Uniform Straight Line Acceleration
vf = vi + at