PHY131H1S - Class 7
Today:
• Review for tomorrow’s test
• In tba, 6:00 – 7:30pm
• On Chapters 1-3, Error
Analysis Mini-Document,
and Sections 4.1 through
4.4.
• Bring a calculator and one
8.5x11’ aid sheet which
you prepare, double-sided
• You drop a glass barometer from
the top of McLennan Physical
Labs. A short time later, before
the barometer hits the ground,
you drop a bottle of scotch. As
they fall, the distance between
the barometer and bottle
A.decreases
B.increases
C.stays the same.
Niels Bohr
Relative Motion
• Example 1: A passenger walks toward
the front of the train at 5 m/s. The train is
moving at 36 m/s. What is the speed of
the passenger relative to the ground?
• Example 2: Car A is traveling at 25.0 m/s
E toward Bloor and Keele. Car B is
traveling at 15.8 m/s N toward Bloor and
Keele. Just before they collide, what is
the velocity of car A relative to car B?
A particle moves from position 1 to
position 2 during the interval ∆t.
Which vector shows the particle’s
average velocity?
During which time interval is the
particle described by these position
graphs at rest?
A. 0–1 s
B. 1–2 s
C. 2–3 s
D. 3–4 s
A 50 g ball rolls off a table and lands
2 m from the base of the table. A 100
g ball rolls off the same table with the
same speed. It lands at a distance
A. less than 2 m from the base.
B. 2 m from the base.
C. greater than 2 m from the base.
The Gaussian:
68% of data
between the
dotted lines on
the graph.
Mean and Standard Deviation of a
set of numbers
• Repeat the same measurement N times. You
measure the values x1, x2, x3, …, xN. In other
words, you measure xi, where i is an index which
ranges from 1 up to N.
N
1
• The estimated mean is x   x i
N
i1
• The estimated standard deviation is
N
1
2
 
(x

x
)

N 1 i1 i
• You can estimate that σ is the error in any
individual measurement xi : Δxi = σ.
Propagation of Errors
z = A x
Δz = A Δx
Repeated Measurements
• Repeated n times
• Each individual measurement has an
error of precision Dx
Motion with Constant Acceleration:
another useful equation!
Does not contain si or sf !
Does not contain vfs !
Does not contain Dt !
v is  v fs 
sf  si  
Dt
 2 
This is just the
average speed.
Does not contain as!
(..but it does require
that as is a constant.)
Projectile Motion Example
• A car drives off a cliff of height d with
speed v0.
• The ground is horizontal both at the
top and bottom of the cliff.
• How far from the base of the cliff does
the car land?
Before Class 8 on Wednesday
• Test is tomorrow! tba, 6:00pm.
• On Chs. 1-3, Error Analysis, and Sections 4.1
through 4.4.
• Bring a calculator and one 8.5x11’ aid sheet which
you prepare, double-sided
• By Wednesday, please finish reading Chapter 4
• Something to think about: You are driving North
Highway 427, on the smoothly curving part that will
join to the Westbound 401. Your speedometer is
constant at 115 km/hr. Your steering wheel is not
rotating, but it is turned to the left to follow the curve
of the highway. Are you accelerating? If so, in what
direction?