Transcript What is Physics?

What is Physics?
Physics is…
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The science of the study of energy
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Involved on the atomic level (like what we just
covered in Semester 1)
Involved in moving large objects (like cars,
people…)
And waves
Who was Newton?
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Considered to be the father of physics
Came up with some basic laws
Great mathematician
Who was Einstein?
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Another great scientist and mathematician
Famous equation: E = mc2
Objectives
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Determine relative motion between objects
Recognize displacement of an object
Relate speed to distance and time
Distinguish between speed and velocity
Recognize that all moving objects have
momentum
• Solve problems involving time, distance,
velocity, acceleration, and momentum
Objectives, cont.
• Interpret graphs and determine slope of a
graph
• Know the difference between scalars and
vectors and find resultant vectors
• Define and use acceleration
• Know and use Newton’s Laws of motion
that include: mass, inertia, weight, and
force
Other terms:
• Centripetal force, gravity, potential energy,
kinetic energy
• Types of forces: weak, strong,
gravitational, and electromagnetic
Motion
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Physicists study motion of large objects first
because they are easy to see
There is some math involved so you will
need your circle sheets to help you keep
track and make the learning move more
smoothly…
The formulas of motion
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Speed = distance
time
V=d
t
d
V
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Momentum =
.
r=mv
Mass x velocity
r
Write these formulae
on your triangle Sheet.
m v
t
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To compare speeds of various objects
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Humans 5.0 km/h
Horse 68 km/h
Eagle 184 km/h
Race car 346 km/h
Jet 925 km/h
Distance-Time Values for a Racing Car
Time (s)
Distance (m)
0
0
1
96
2
192
3
288
4
384
Graph of distance versus time
600
500
400
300
200
100
0
0
Dist. (m)
jet
eagle
car
horse
walker
2.5
Time (s)
5
7.5
10
Terms
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Speed – distance traveled divided by
the time interval during which the
motion occurred
Velocity – speed in a specific
direction
Samples:
90 m/s is a speed
90 m/s north is a velocity
Speed is a scalar. It has only a number with units (called a
magnitude).
Other samples of scalars:
mass (5.00 kg)
volume (395 g/cm3)
Velocity is a vector. It has magnitude and direction
Other samples of vectors:
weight (70.0 n down)
acceleration (35.0 m/s2 East)
Vectors are shown with arrows
5 m/s E
3 m/s W
Vectors “add” if they are in the same direction
2 m/s E +1 m/s E = 3 m/s E
+
=
Vectors “subtract” if they are in opposite
directions.
+
=
2 m/s E - 1 m/s W = 1 m/s E
Find the velocity in meters per second
of a swimmer who swims exactly 110
m toward the shore in 72 s.
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V = d = 110m = 1.5 m toward the shore
t
72s
s
d
V
.
t
Find the distance traveled by a horse
that is moving at 68 km/h if it runs for
45 minutes. Answer in meters.
d = vt
45 min = .75 h
d = 68km .75 h = 51 km
h
d = 51 km
Ans: 51,000 m
1000m
km
d
V
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t
Metric system - distance
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km hm dam m dm cm mm
From where you start, count the number
places that you move to get to the desired
unit. Move decimal point that number and in
that direction.
We start at km and go three spaces to right
to m. Move decimal 3 to the right… so 51
becomes 51000
Velocity assignment
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See next slide
Read the sample then do
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Practice 1. - 4.
Momentum, r
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Greek letter “rho”
The product of the mass of an object and its
velocity
r=mv
Units:
kg m
s
Momentum problem
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What is the momentum of a 0.8 kg kitten
running to the left at 6.5 m/s?
r = m v = 0.8 kg (6.5 m/s)
r = 5 kg m/s to the left
Anything that moves has momentum
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Heavy objects (trains) moving slowly have
large momentum and are difficult to stop.
Very small objects (bullets) moving very fast
have large momentum and are difficult to
stop but easy to get moving.
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Assignment: next slide / do practice 1abde
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Activity on the next slide
• Real World Applications
• In groups of no more than 3, complete the
assignment. Equipment: paper, ruler,
calculator. Complete spreadsheet in Life
Skills class.
1. One cover sheet is due per group
2. Each group member is responsible for
doing each of the following:
a. determine how far the hikers travel
by measuring distance from Ambition Lake
to Blackcap Mountain.
b. using legend at bottom of map,
determine time to walk the distance at the
rate of 5km/hr.
Determine altitude change
c. Using the given altitudes in #1 on page
222, determine the number of meters
they climb (change in altitude).
d. Using the climbing rate of 600 m/ hr,
determine how much time it takes to
climb from the lake to the mountain.
e. Add the walking time and the climbing
time to calculate how long (in hours) it
will take the hikers to reach their
destination.
3. Create a spreadsheet using Excel
in Life Skills class that applies Naismith’s
rule. (This rule is discussed on page 222 in
our book.)
a. Your spreadsheet headings could
include:
time / distance walked
time / distance climbed
b. if time permits (for extra points)
make a graph of 1) Distance walked vs
time and 2) Distance climbed vs time
I am
king of
the hill!