Pick up graded homework from front Turn in homework in …. Time graphs Δx = = x f – x i v = = Δx /Δt a = = Δv /Δt − − Case 1: A student walking across campus to class at
Post on 27-May-2018
218 Views
Preview:
Transcript
How I graded homework I was thorough and lenient!
A’s (4.0) were given if it was complete, and thought was given to every question
C’s (2.0) were given if a number of problems were not completed, or no work was included (or late)
F’s (zeros) were only given if you turned nothing in Pay attention to comments, and if I suggest you come to
office hours, please do!
Common issues: Polar coordinates Free fall Velocity/acceleration confusion
Did not receive homework from
Galaviz Hamilton Moua T. Nguyen Ochoa Ngo
If you are not officially added yet, your name might not be listed here even though I have not received homework from you.
Before we start
Get in small groups (lets try 3) Discuss any issues you had with the
homework Help your group-mates with their difficulties (5 minutes)
Any further Issues:
See me in office hours Make an appointment with me Set up a time to meet with some classmates Ask your workshop facilitator for help Physics Club? Peer connections (drop in tutoring): http://peerconnections.sjsu.edu/
Last time: Multiple choice
An object with a positive velocity (+3m/s for example) indicates the object must: A. Be speeding up B. Be traveling in a positive direction C. Have a positive acceleration D. Have a positive displacement E. Both A & B
Multiple choice
An object with a positive velocity (+3m/s for example) indicates the object must: A. Be speeding up B. Be traveling in a positive direction C. Have a positive acceleration D. Have a positive displacement E. Both A & B
v=Δx/t t is always positive therefore if v is positive Δx is also positive
Multiple choice
An object with a positive velocity (+3m/s for example) indicates the object must: A. Be speeding up B. Be traveling in a positive direction C. Have a positive acceleration D. Have a positive final distance E. Both A & B
Unit Conversion
Convert 20 inches to centimeters: *Remember multiplying by 1 gives us the same quantity back! 5 x 1 = 5 20.0 inches x 2.54 centimeters
1 inch = 20.0 x 2.54 = 50.8 centimeters
Learn this!
Updated since class: correct values and sig figs
You try:
Convert 100 miles/hour into meters/second 1 mile ~ 1610 meters 100 miles x 1 hour x 1 min x 1610 meters hour 60 min 60 sec 1 mile = 44.72 meters second
Position, Velocity & Acceleration vs. Time graphs
Δx = xf – xi v = Δx/Δt a = Δv/Δt = = = − −
Case 1: A student walking across campus to class at a constant speed.
t
x
tf
Distance changing at a constant rate.
t
v
tf
Velocity is constant and positive.
tf t
a
Acceleration is zero because velocity is not changing.
Check-In Clicker question
A. I am very confident in my understanding of these graphs and ability to produce them
B. I think I might need to study a bit more, but I feel ok with them
C. I will need to seek help to learn these
D. I am completely lost
Review on Limits
v = lim Δs/Δt (or v=dx/dt in calculus) Δt 0
x
t the line tangent to the position vs. time graph is defined to be the instantaneous velocity at that time
v = lim Δx/Δt (or v=dx/dt)
t
x
tf t
x
tf
Δt 0
the line tangent to the position vs. time graph is defined to be the instantaneous velocity at that time
Graphical Instantaneous Velocity
Average velocities are the blue lines
The green line (tangent) is the instantaneous velocity
Section 2.2
Instantaneous Velocity
The limit of the average velocity as the time interval becomes infinitesimally short, or as the time interval approaches zero
The instantaneous velocity indicates what is happening at every point of time The magnitude of the instantaneous velocity is what
you read on a car’s speedometer
Section 2.2
Free Fall
A freely falling object is any object moving freely under the influence of gravity alone Free fall does not depend on the object’s original
motion
All objects falling near the earth’s surface fall with a constant acceleration
The acceleration is called the acceleration due to gravity, and indicated by g
Section 2.6
Free Fall
g = acceleration due to gravity g x mass = weight = force of the earth pulling on you Convention: The direction of the pull of the earth is downwards, therefore a = -g = -9.81. (in the –y direction)
Common Confusions
Pg 43 : The value of g decreases with increasing altitude…. at Earth’s surface g is equal to 9.81m/s
G varies for VERY large distances, it’s negligible at Earth’s surface
Clicker Question
Which of the following is true? For a freely falling object:
A. Acceleration is always downwards B. Acceleration is downwards only when the
object is traveling downwards (past max height)
C. Acceleration is zero at max height D. Acceleration is constant E. Both A and D
top related