Transcript Acceleration

Physics Topics
1.
2.
3.
4.
5.
6.
7.
Motion
Measuring Matter
Work, Power, Machines
Newton’s Laws
Waves
Momentum
Pressure
Acceleration is the rate of
change in the speed of an
object.
 Positive
acceleration
and positive
speed
 Negative
acceleration
and positive
speed
Acceleration
(m/sec2)
Change in speed (m/sec)
=
Change in time (sec)




A student conducts an
acceleration experiment by
coasting a bicycle down a
steep hill.
The student records the speed
of the bicycle every second for
five seconds.
Calculate the acceleration of
the bicycle.
Constant acceleration is different from constant
speed.
 Motion with zero acceleration appears as a straight
horizontal line on a speed versus time graph.

zero acceleration
constant speed
Constant acceleration is sometimes called uniform
acceleration.
 A ball rolling down a straight ramp has constant
acceleration.

constant acceleration
increasing speed



An object can have acceleration, but no speed.
Consider a ball rolling up a ramp.
As the ball slows down, eventually its speed
becomes zero.
constant negative
acceleration
decreasing speed
MASS,
VOLUME, &
DENSITY
Definition: Amount of
matter in an object
Units: kg or g
 Mass is different from
weight because…Weight
depends on pull of gravity
 Definition: How much space an
object takes up
 Regular shaped object (box) then
V= L x W x H (cm3 or m3)
 Liquids - to find volume…use
graduated cylinder (mL or L)
 Use graduated cylinder for odd
shaped solid objects (cm3 or m3)
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
Obtain a clean graduated
cylinder.
Fill the graduated cylinder with
enough water to cover object.
Record the volume
Carefully place the object into the
water filled graduated cylinder.
Record the new water level.
The volume of the object is the
Vfinal – Vinitial
 Density is the measurement of
the mass of an object per unit
volume of that object.
 Formula:
D (density) = m (mass)
V(volume)


A rock has a mass of 25.7 grams and a
volume of 3.56 cm3. Find the density.
1st write: D = mass
volume

2nd: Substitute in the measurements
D = 25.6 g
3.56 cm3

3rd: Calculate following sig fig rules.
Density = 7.19 g/ cm3
 Calculate the density of a marble
that has a mass of 13.6 grams and
a volume of 6.1 cm3.
 D = m/V
= 13.6 g / 6.1 cm3
 D = m/V = 2.2 g / cm3
 If you pack more mass into
the same volume, it is more
dense.
 Example: packing wet sand
into a bucket
 If you pack the SAME mass into a
SMALLER volume, it is MORE
dense
 Example: a trash compactor.
Just because something
has more mass DOES
NOT mean it is more
DENSE.
Force
40 N
Distance
10 m
Force acting through a distance
W=F*d
= 40 N * 10 m = 400 Joules
 Force must be in same direction as
distance
Force
Distance
Work Input is always greater than Work Output due to Friction
% Efficiency = Work Output / Work Input *100
Work Input
Feffort*distance
10N*5m = 50J
Work Output
Fresistance*distance
20N*2m = 40J
Work Input is always greater than Work Output due to Friction
% Efficiency =
(40 J / 50 J)
Work Input
= 0.8
Work Output
Feffort*distance
Fresistance*distance
10N*5m = 50J
20N*2m = 40J
 I. Law of Inertia
<>
 II. F = ma
 III. Action / Reaction
A force is…
a push or a pull.
Friction, Drag, Gravity, and Weight are
forces…
Law I: Inertia vs. Mass
Bigger masses have more…
Smaller masses have less inertia.
But inertia does not equal mass.
Newton’s
2nd Law:
F = ma
Force equals mass x acceleration
F = ma
mass = 10 kg
acceleration = 2 m/s
Find the Force.
2
F = 10 kg x 2 m/s = 20 N
2
Newton’s
3rd Law:
Action
Reaction
You exert force on the
weights and…
The weights exert the
same force on you.
Water is pushed back
and…
the boat is pushed forward.
Physics FCAT
Dr. Persin
What are waves?
a wave is a disturbance that
travels away from a source.
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 sound waves
 visible light waves
 radio waves
 microwaves
 water waves
 sine waves
 telephone chord waves
 stadium waves
 earthquake waves
 waves on a string
 slinky waves
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 Waves transfer energy with
transferring matter.
 Lets do a Stadium Wave!
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
A wave transfers energy from place to
place.

What carries waves?

A medium, a medium is the material
through which a wave travels.

A medium can be a gas, liquid, or solid.

Waves are created
when a source of
energy causes a
medium to vibrate.

A vibration is a
repeated back and
forth or up and down
motion.
v = velocity
f = frequency
l = wavelength
v = velocity, m/s
f = frequency, Hertz (Hz)
λ = wavelength, m
λ is the Greek letter “lambda”
 Calculate the velocity of a wave
with a frequency of 250 Hz and a
wavelength of 3 m.
v = f
l = 250 Hz  3 m
 v = 750 m/s
Momentum
= mass * velocity
What is momentum?
All objects have mass.
So if an object is moving,
then it has momentum.
It is mass in motion.
Equation: p = m V
Determine the momentum of a ...
a. 60 kg body moving at 9 m/s.
b. 1000 kg car moving at 20 m/s.
c. 40 kg freshman moving at 2 m/s
Answers:
a. 540 kg m/s b. 20,000 kg m/s c. 80 kg m/s
Conceptual Check:
If the boulder and the
boy have the same
momentum,
will the boulder crush
the boy?
Hint: Which would have
the larger speed?
Conceptual Check:
Which has a greater momentum, a skateboard
moving at 3 m/s or a stationary ten-wheeler
truck ? Explain your answer.
When can a ball have the same momentum as
an airplane parked on a runway? Explain
your answer.
Momentum Rocket = Momentum Exhaust
A 20 kg rocket zooms upward at 5
meter/second. At the same exact time, 10 kg of
water shoots downward. How fast does the
water shoot out?
Here is an example.
FCAT Physics: Part III.
Pressure
A woman’s high heels
sink into the soft
ground,
but the larger shoes
of the much bigger
man do not. Why? More
Pressure.
Pressure = Force / Area
 Calculate the pressure exerted by a
heel of a shoe with an area of .02 m2 if
the force of the heel is 50 N.
P = F / A
= 50 N / .02
 P = 2500 N / m2
2
m
More nails means less pressure from each one.
Get the point!
The End.