Transcript Classifying Matter and the Periodic Table

0014 Force, Mass and Motion: 1. distinguish
between mass and weight of an object.
Mass
• Quantity of matter in
an object
• The measurement of
inertia
• Brick = 1kg
vs
Weight
• The gravitational
force exerted on an
object by the nearest,
most massive body
(Earth)
• Brick = 2.2 pounds
The Newton (metric unit)
• In the metric system, the unit of weight, or
any other force, is the newton, which is
equal to a little less than a quarter pound.
• Newton = force needed to accelerate 1 kg 1 m/s2
• 1 kg brick weighs about 10 N
• Or a baseball = 1 N
0014 Force, Mass and Motion: 2. identify
characteristics of forces that act on objects (e.g. frictional,
gravitational)
0014 Force, Mass and Motion: 3. determine
the relationship between the velocity and acceleration of an
object.
Acceleration
• Acceleration is the amount of change in
velocity divided by the time it takes the
change to occur.
• Acceleration (m/s2) =
[final velocity – initial velocity (m/s)] / time (s)
• A = (vf - vi) / t
A car traveling at a rate of 10 m/s
accelerates to 90 m/s in 12 seconds.
Calculate its acceleration.
• A = (vf - vi) / t
• A = 90 m/s – 10 m/s / 12 s
= 80 m/s / 12 s
= 6.67 m/s/s
or 6.67 m/s2
3 devices in your car make it accelerate:
•
•
•
•
Accelerator pedal
Brake pedal
Steering wheel
Whenever an object changes speed or
direction it accelerates.
Figure 2-8
Galileo’s falling-ball apparatus with a table of
measurements and a graph of distance versus time.
Galileo found the following:
• a ball rolling down a ramp moves with
constant acceleration
• a ball attains a greater acceleration from
steeper inclines
• regardless of weight, when air resistance
is negligible, all objects fall with the
same acceleration
Free-Fall Velocity
• The velocity of a falling object is
proportional to the length of time it has
been falling.
• Velocity (m/s) = constant g (m/s2) x time (s)
• V=gxt
• Galileo found g = 9.8 m/s2
Acceleration due to Gravity
• Suppose a falling rock is equipped with a
speedometer:
• In each succeeding second of fall, the rock’s
speed increases by the same amount: 10 m/s
• Time of Fall (s) Instantaneous Speed (m/s)
• 1
10
• 2
20
• 3
30
• 4
40
5
50
Gravity
• Suppose a falling rock is equipped with
an odometer:
• The readings would indicate that the
distance fallen increases with time
according to the relationship d = ½ gt2
• Time of Fall (s)
Distance of Fall (m)
–
–
–
–
1
2
3
4
5
20
45
80
Free Fall and Air Resistance
• In free-fall, force of air
resistance counters force
of gravity.
• As skydiver falls, air
resistance increases ‘til it
approaches the magnitude
of the force of gravity.
Once the force of air
resistance is as large as the
force of gravity, skydiver
is said to have reached a
terminal velocity.
• Skydiving
0014 Force, Mass and Motion: 4. solve
quantitative problems involving force, mass, and motion of
objects.
0014 Force, Mass and Motion: 5. demonstrate
knowledge of Newton’s 3 laws of motion and their
application to everyday situations.
Isaac Newton and
the Universal Laws of Motion
• English scientist
(1642-1727)
• Synthesized the work
of Galileo and others
• 3 laws describe all
motion
First Law: Inertia
(matter resists change)
• A moving object will continue moving in a
straight line at a constant speed, and a
stationary object will remain at rest, unless
acted upon by an unbalanced force.
• animation
Second Law: F = m x a
• The acceleration produced by a force on an
object is proportional to the magnitude of
the force, and inversely proportional to the
mass of the object.
• tutorial
Third Law: action / reaction
• For every action there is an equal and
opposite reaction.
• See some examples
calculate the force needed to produce a
given acceleration on a given mass
(F = ma)
• A 20 kg mass has an acceleration of 3 m/s2.
Calculate the force acting on the mass.
• F = (20 kg) (3 m/s2)
• F = 60 kg m/s2 = 60 N
What force is needed to accelerate a 75 kg
sprinter from rest to a speed of 10 meters
per second in half a second?
• First find acceleration.
Accel = final vel – initial vel (m/s) / time (s)
= 10 m/s – 0 m/s / .5 s = 20 m/s/s
• Force (N) = mass (kg) x accel (m/s2)
F = 75 kg x 20 m/s2
F = 1500 N
Newton’s Law of Universal
Gravitation
• Between any two objects in the universe there
is an attractive force proportional to the
masses of the objects and inversely
proportional to the square of the distance
between them.
• F = (G x m1 x m2) / d2
• The more massive 2 objects are, the greater
the force between them.
• The farther apart 2 objects are, the less the
force between them.
Figure 2-13
An apple falling, a ball being thrown, a space shuttle
orbiting the Earth, and the orbiting Moon, all display the
influence of the force of gravity.
0014 Force, Mass and Motion: 6. apply
knowledge of the concepts of work and power to the
analysis of everyday activities.
Work is done when
a force is exerted
over a distance.
Work
• is equal to the force that is exerted times
the distance over which it is exerted.
• W=Fxd
• The unit of work combines the unit of
force (N) with the unit of distance (m)
• Newton-meter (N-m) aka Joule.
You carry a 20 kg suitcase upstairs, a distance of
4m. How much work did you do?
•
•
•
•
•
•
W=Fxd
F = ma
= (20 kg) (10m/s2) = 200 N
W=Fxd
= (200 N) (4m)
= 800 J
Power
• measures rate at which work is done.
• Power is the amount of work done,
divided by the time it takes to do it.
• Power (watts) = work (joules) / time
(sec)
• P = W/t
Power
• Since work performed equals energy
expended,
• Power (watts) = energy (joules) / time (sec)
• The watt is defined as the expenditure of
1 joule of energy in 1 second.
(75 watt light bulb consumes 75 J/sec)
0014 Force, Mass and Motion: 7. demonstrate
knowledge of types and characteristics of simple machines
and their effect on work.
“Simple Machine:
device for
multiplying or
changing the
direction of force.