Domain 5 Student PP Notes Forces, Waves, and Electricity (26% of the test)
Velocity (speed with a direction)
1. a measure of how fast something is moving
2. the distance traveled in a given amount of time
The formula from the SCIENCE FACTS AND FORMULAS sheet is
Velocity (V) = d where d = distance, t = time
T
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
t = 1.5 hrs
speed = distance = 21
time
1.5
speed = 14 mph
Acceleration
1. the rate at which velocity changes
2. formula:
final velocity - initial velocity
acceleration =
time
or from SCIENCE FACTS AND FORMULAS sheet
Acceleration = Change in Velocity/Time Elapsed
V  V0 

a 

t


Sample Problem - If a car accelerates from 5 m/s to 15 m/s in 2 seconds, what is the car's
average acceleration?
a = v – vo = 15 – 5
t
2
a = 5 m/s/s
v = 15 m/s
vo = 5 m/s
t=2s
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.
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.
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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
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.
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.
Gravity
1. Gravity is the force of attraction between any two objects.
2. The Law of Gravitation states that any two masses exert an
attractive force on each other. The amount of attraction depends
upon two things: the mass of the objects and the distance
between the objects.
3. What is gravitational acceleration?
A. When objects fall, they accelerate toward the ground.
B. Using Newton’s 2nd Law we can see this relationship: F = ma
C. The force caused by gravity acts upon a certain mass to cause it to
accelerate toward the ground at a constant rate.
D. Acceleration due to gravity is 9.8 m/s2
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4. The force of gravity experienced by something is also known as its weight.
Weight can be calculated multiplying mass by the acceleration of gravity.
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.
The force of gravity (weight) are both measured in Newtons. Mass is measured in
kilograms. Acceleration is measured in m/s/s (m/s2).
Work
1.
two conditions must be met for work to occur
a. the object must move through a distance
b. a force must act upon the object in the direction
the object moves
2.
SI unit for work is the joule, J. (Newton-meter)
3.
Formula from the SCIENCE FACTS AND FORMULAS sheet
4. :work = force X distance W=F X d
Sample Problem: What work is done if Hernando uses 88 N of force to pull a table
12 meters?
F = 88 N
W=Fxd
d = 12 m
W = (88)(12)
W = 1056 J
Waves
1. All waves transport energy without transporting matter..
2. Waves can be classified waves into two categories on the basis of their ability or
inability to transmit energy through a vacuum (i.e., empty space).
A. Electromagnetic waves are capable of transmitting its energy through a vacuum
(i.e., empty space).
1) Electromagnetic waves are produced by the motion of charged particles.
2) Electromagnetic waves which are produced on the sun subsequently travel
to Earth through the vacuum of outer space.
B. A mechanical wave is a wave which is NOT capable of transmitting its
energy through a vacuum.
1) Mechanical waves require a medium in order to transport their energy from
one location to another.
2) There are two types of mechanical waves, transverse and
longitudinal
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Increasing energy
Increasing frequency
Decreasing wavelength
What are frequency and wavelength?
A wave’s frequency is the number of wave cycles the particles in a wave go through
in one second.
One wave cycle is equal to one wavelength.
Frequency is measured in hertz.
X-rays and gamma-rays are usually described in terms of energy, visible and
infrared light in terms of wavelength, and radio in terms of frequency.
Wave Interactions
1. Reflection occurs when a wave strikes an object that does NOT absorb the wave’s
energy and bounces back off of it.
2. Refraction occurs when a wave travels at an angle from one medium to another in
which its speed is different.
3. Diffraction involves the bending of waves around obstacles.
4. Wave interference is the phenomenon which occurs when two waves meet while
traveling through the same medium.
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Refraction
1. Refraction occurs when a wave travels at an angle
from one medium
to another in which its speed is
different.
2. The difference in speed causes the wave to bend.
3. Refraction is why objects in a pool are difficult to
locate when viewed from above and why a pencil
looks broken when part of it is placed in a glass of
water.
Diffraction
1. Diffraction involves the
bending of waves
around obstacles.
2. Diffraction can occur with any kind of
wave.
3. Diffraction explains why sound can be
heard around corners.
Interference
1. Constructive interference occurs when two
waves disturb the medium in the same way. The
disturbance is
2. larger than the disturbance of either wave separately.
3. Destructive interference is canceling interference that
occurs when two waves disturb
the medium in opposite ways. The
disturbance is smaller than the
disturbance of either wave separately.
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Sound
1. Sound waves are mechanical waves, meaning they must have a
medium to travel through. (There is NO sound in space.) A sound wave is a
longitudinal wave.
2. Sound travels fastest in solids, second fastest in liquids, and slowest in gases.
3. As the temperature increases, the speed of sound also increases.
4. Different sounds appear different because they have different pitch or frequency.
Doppler effect
1. DE is a change in the
observed frequency
of a wave, as of sound or
light, occurring when the
source and observer are in
motion relative to
each other.
2. The frequency increases when
the source and observer
approach each other and
decreases when they move apart.
3. The Doppler effect can be observed for any type of wave - water wave, sound
wave, light wave, etc
How are electricity and magnetism related?
1. They cause each other.
a. North and South relate to magnets
b. (+) and (-) relate to electricity
2. Magnetic fields are created by moving charges.
Electromagnetic Forces
1. Like charges (poles) repel each other, opposite charges (poles)
attract.
2. As the distance between the charges increases, the size of the force
decreases. The same holds true for magnets.
3. Magnets will always have a North Pole and a South Pole.
Electric and Magnetic Field Lines
1. The lines always go from positive charges to negative charges and from north
poles to south poles.
2. The closer the magnetic field is strongest where the lines are closer together.
3. The closer lines, the stronger the field.
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What is an electromagnet?
A. An electromagnet is a temporary magnet caused by an electrical current.
B. It has a magnetic force ONLY when an electric current moves through the wire.
C. The electromagnet does not work if the current is switched off.
D. Electricity can be used to temporarily align the magnetic domains within a piece of
iron in order to create an electromagnet.
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 nail
b. more batteries (more current)
c. iron core present
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