Domain 5 Teacher Notes – SPS8abcde
I. Motion
A. Newton’s Laws of Motion
1. The Law of Inertia or Newton’s First Law: An
object at rest tends to stay at rest and an object
in motion tends to remain in motion in a
straight-line path unless acted on by an
unbalanced force.
a. Inertia is another word for mass. The more
mass an object has, the greater its tendency
to maintain its current state.
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b. Applications:
i. People are often thrown from automobiles
in wrecks because the car comes to a
sudden stop, but the person has a
tendency to stay in motion.
ii. The ride is much smoother on a cruise ship
than a fishing boat, because the cruise ship
is more massive and is not affected as
much by the waves.
2. Newton’s Second Law: The acceleration of an
object is directly proportional to the applied force
and inversely proportional to its mass.
F=ma F= force
m = mass
a = acceleration
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Sample Problem: What is the force exerted by a
2 kg mass that accelerates at 3 m/sec/sec?
mass=2 kg F=ma
acceleration=3 m/sec/sec F =2 kg x 3 m/sec/sec
F=6 kilogram×meter/sec/sec
Check the SCIENCE FACTS AND FORMULAS sheet
1 newton = 1 kilogram×meter/second/second
So the correct answer is 6 newtons.
3. Newton’s Third Law: For every action there is an
equal and opposite reaction.
a. If object A exerts a force on object B, then
object B exerts an equal force on object A in
the opposite direction.
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b. Consequences: Forces always exist in pairs. It
is impossible for you to push on something
without it pushing back. Newton’s Third law
can be used to explain the motion of rockets
and balloons. As the gases exit the balloon or
rocket, they push it in the opposite direction.
B. Motion depends on the observer’s frame of
Reference.
C. Speed
1. A measure of how fast something is moving
2. The distance traveled in a given amount of time
3. Formula speed = distance
time
4. Sample Problem: A bicyclist rides for 1.5 hours
from Snellville to downtown Atlanta. He travels 21
miles. What is his average speed?
d=21 miles speed=distance
t=1.5 hours time
speed= 21 miles
1.5 hours
Speed = 14 mi/hr
D. Velocity
1. Speed in a particular direction
2. formula: velocity = distance and direction
Time
The formula from the SCIENCE FACTS AND FORMULAS sheet is Velocity (V) = V0 + at, where V0 = Initial Velocity, a = Acceleration, and t = Time
3. Sample Problem: What is the average velocity of
a commercial jet that travels west from New York
to Los Angeles (4800 km) in 6.00 hours?
Velocity = distance
time
= 4800 km
6.00 hours
= 800 km/hr west
E. Acceleration
1. The rate at which velocity changes
2. formula: final velocity-initial velocity
acceleration = time
or acceleration =
from SCIENCE FACTS AND FORMULAS sheet
Acceleration = Change in Velocity/Time Elapsed
3. Acceleration occurs if either of these two
conditions exist.
a. The speed of an object is changing. It can be
increasing or decreasing.
The direction of the movement is changing.
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4. Sample Problem: If a car accelerates from 5 m/s to
15 m/s in 2 seconds, what is the car's average
acceleration?
V = 15 m/s
Vo = 5 m/s a= 15 m/s - 5 m/s
t = 2 sec 2 sec
a= 5
II. Forces
Gravitational
The force of gravity between any two objects increases as the mass of either object increases. The force of gravity decreases as the distance between the objects increases.
The force of gravity experienced by something is also known as its weight. Weight can be calculated multiplying mass by the acceleration of gravity (g).
W=mg
Weight depends on both mass and the acceleration of gravity. Mass depends only on the amount of matter in an object. Mass does not change when the location of an object changes.
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The force and weight are both measured in Newtons.
Mass is measured in kilograms. Acceleration is
measured in m/s/s (m/s2).
3. Free Fall
a. A free-falling object is an object which is falling
under the sole influence of gravity.
b. Free-falling objects do not encounter air
resistance.
c. All free-falling objects (on Earth) accelerate
downwards at a rate of approximately 10 m/s/s
(to be more exact, 9.8 m/s/s). This quantity
known as the acceleration of gravity has a
special symbol to denote it - the symbol g.
The distance traveled by a falling object is
calculated using the formula, d = ½ gt2
d. Sample problem: A rock is dropped from the
top of a cliff and strikes the ground 6.5
seconds later. How high is the cliff in meters?
g=9.8 m/sec2 d = ½ gt2
t = 6.5 sec = ½ (9.8 m/sec2) (6.5 sec)2
= ½ (9.8 m/sec2) (42.25 sec2)
= ½ (414.05 m)
= 207 m
Electromagnetic Forces – Like charges repel each
other, opposite charges attract.
1. As the distance between the charges increase, the
magnitude of the force decreases. The same holds
true for magnets.
2. Magnets will always have a North Pole and a South
Pole. Just like with electrical charges, opposite
poles attract. While it is possible to separate
positive and negative charges, it is impossible
to separate north and south magnetic poles.
3. Electric and Magnetic Field Lines- The lines always
go from positive charges to negative charges and
from north poles to south poles. The closer the
Magnetic field is strongest where the lines are closer together
lines, the stronger the field.
1.List a use for electromagnets.
Lift and move cars in a junk yard
2. How can you make a stronger
electromagnet?
a. More coils of wire around the nail
b. More batteries
Electromagnet
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Work
two conditions must be met for work to occur
the object must move through a distance
a force must act upon the object in the direction the object moves
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SI unit for work is the joule, J. (Newton-meter)
Formula: work = force X distance W=F X d
When an object is lifted to a new location or pushed
up a ramp, the work equals the potential energy
gained.
5. Sample Problem: What work is done if Hernando
uses 88 N of force to pull a table 12 meters?
F = 88N Use the formula W=F X d
d = 12 m from the W=88N X 12 m
SCIENCE FACTS AND FORMULAS sheet W= 1056 N-m or
1056 J
Power
the rate of work
SI unit is the watt, W (joule/second)
formula: power = work/time (work divided by time)
4. Sample Problem: When doing a chin-up, a physics
student lifts her 40-kg body [which has a force (weight) of 400 N] a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps?
You must first calculate the work done to lift her body
W = F X d
= (400 N) (0.25 m)
W = 100 J
To calculate power
Power= work
time
Power=100 J
2 sec
Power = 50 Watts
III. Energy
Law of conservation of energy.
Energy can neither be created nor destroyed.
It can be changed into other forms.
Two kinds of energy
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Potential energy is stored energy or energy of position. Examples: Magnetic, gravitational, chemical, elastic, and nuclear
PE = mgh where m= mass
g = acceleration due to gravity
h = height
Kinetic energy is energy of motion or energy in action. Examples: a moving baseball or a roller coaster going downhill
KE = ½ mv2
Forms of energy
mechanical energy
Any object which possesses mechanical energy - whether it be in the form of potential energy or kinetic energy - is able to do work. That is, its mechanical energy enables that object to apply a force to another object in order to cause it to be displaced.
b. Simple machines help us lift, pull, increase
elevation of heavy things, change the direction of
the force, increase the force, split things, fasten
things, and cut things
i. inclined plane - Ramp, stairs
ii. wedge – two inclined planes back to back –
screwdriver, knife, axe
iii. screw – inclined plane wrapped around a
cylinder
iv. pulley – rope revolves around a fixed point;
more pulleys make work easier
v. lever – has a fulcrum – see-saw
vi. wheel and axle – bicycle, car, doorknob,
screwdriver in use
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mechanical advantage-the number of times a machine multiplies an effort force.
Formulas from formula sheet:
Actual Mechanical Advantage:
where FR is Force due to resistance and FE is Force due to effort
IMA= Effort Length
Resistance Length
Sample Problem: In a pulley set-up, an effort force of 50 Newtons lifts a resistance force of 100 Newtons. What is the MA of the pulley system?
IMA= Effort Length
Resistance Length
Think about which formula to use
or
AMA= Fr M.A. = 100N
Fe 50N
M.A = 2
Heat, Temperature and Internal Energy
The temperature of an object is directly proportional to the average kinetic energy of its particles. As temperature goes up, particles move faster.
The Internal Energy of a substance is total of the potential and kinetic energy of all its particles.
Energy moving from one location to another is known as heat. Objects do not contain heat. Instead they contain internal energy.
Chemical energy relates to potential energy stored in the bonds between atoms in a compound.
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