Download Forces Powerpoint Review

The Science Test
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Motion- change in position of an object;
occurs when a force acts on an object
Speed- rate of change in object’s position
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speed= distance/time
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or V= d/t
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Displacement vs. distance - displacement has
a direction
Velocity vs. speed – velocity has a direction
Velocity = displacement
time
Acceleration - rate at which velocity changes
Acceleration = final velocity – initial velocity
time
The table describes the
motion of a soccer ball
rolling across a field. Think
about how the ball’s
velocity in meters per
second, changes during
each second of time.
How can you describe the
ball’s motion?
a.
b.
c.
d.
Constant velocity
Negative acceleration
Positive acceleration
Negative velocity
Time (s)
Velocity (m/s)
0
2
1
1.5
2
1
3
0.5
4
0
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A push or pull
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Measured in Newtons
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An object at rest and
an object moving at a
constant velocity is
being acted upon by a
net force of zero
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4 fundamental forces
Gravitational F = G X m1xm2
q1 q2
r
Fe  k 2
r
Electromagnetic - force exerted on a
charged particle in an electromagnetic field
Strong nuclear force – holds the nucleus
together by the exchange of mesons
Weak nuclear force – allows for radioactive
decay, particularly beta
 An object in motion will
stay in motion and an
object at rest will stay at
rest unless acted upon by
an unbalanced force
 Law of Inertia—why we
wear seat belts.
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A moving bowling ball has more inertia than a
soccer ball moving at the same velocity and is
therefore harder to stop.
It has more momentum
Momentum depends on its mass and its
velocity
Which of the following is a measure of an
object’s inertia?
a. Weight
c. volume
b. Mass
d. momentum
What does Newton’s first law of motion state?
When one object exerts a force on a second object, the
second object exerts a force in strength, but opposite
in direction on the first object
b. The force acting on an object is equal to the mass of
the object multiplied by velocity
c. An object at rest remains at rest unless acted upon by
an unbalanced force
a.
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F = ma
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For every action there is an
equal and opposite reaction
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On Earth, all objects fall
with a constant
acceleration of 9.80 m/s2
in the absence of air
resistance.
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In other words, a falling
object’s velocity increases by
9.8 m/s each second it falls!
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Mass—the amount of matter
in an object
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Weight—the force on a body
due to the gravitational
attraction of another body
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Weight changes based on
location.
Mass NEVER changes.
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Two 5 kg balls sit on a table. If one of the balls is replaced
with a 10kg ball, what is the effect on the gravitational
attraction between the two balls?
a. It is about ¼ of what it was
c. it is twice what it was
b. It is about ½ of what it was
d. it is four time what it was
Calculate the weight of an object with a mass of 40 kg.
a. 392 N
b. 400 N
c. 492 N
d. 500 N
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Work = Force x Distance
 Measured in Newton-meters or
Joules
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Power = Work
Time
 Measured in Watts
The pitcher does positive work on the ball
by transferring energy into it. The pitcher
does negative work on it.
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Lever
Inclined plane
Screw
Wheel and axle
Wedge
pulley
A man is holding a very heavy box steady in
his arms. Which of the following describes
the work being done on the box?
a. It is proportional to the force of gravity
acting down
b. It is proportional to the weight of the box
c. It is proportional to the force exerted by the
man holding the box up
d. It is equal to zero because the box is not
moving
A disturbance that transmits energy
through a medium or space
The number of events (waves, vibrations,
oscillations) that pass a point in a given amount
of time, usually a second
 High frequency
(short wavelength)
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Low frequency
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(long wave-length)
Frequency is related to pitch, the higher the
frequency the higher the pitch
Wavelength - the distance between peak to peak ,
shorter wavelengths = higher frequency
 Amplitude- the maximum displacement
 Amplitude is related to intensity, higher the amplitude
the higher the intensity (energy). For sound it means
higher volume.
 Velocity = frequency x wavelength
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Amplitude
EM waves do not require a medium
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Require a medium
Sound is an example of a mechanical wave
Sound travels best in denser materials and
higher temperatures
Earthquakes
Ocean waves
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Reflection—wave
bounces off barrier
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Refraction—wave
changes direction as it
moves from one
medium to another
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Diffraction—the
bending of a wave
around a barrier
Which electromagnetic waves have the highest
energy?
a. Gamma rays
c. radio waves
b. Infrared waves
d. X-rays
What occurs when light hits a clear window?
a. Most of the light is scattered
b. Most of the light is absorbed
c. Most of the light is reflected
d. Most of the light is transmitted
To increase the strength of an electromagnet by
a. Increase the number of coils
b. Increase the number of batteries
Magnetic field is
strongest where the
lines are closest
together
If you break the
magnet, north and
south poles will
reform on each
piece
•The movement of electrons in response
to a field --- Electricity!
•The electromagnetic force is one of the 4
forces of nature and is described by
Coulomb’s Law
Fe  k
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q1 q2
r
2
Charged particles exert forces on each other
Like repels, opposites attract
The greater the distance between the charges
the smaller the force
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Static electricity is
the charge that stays
on an object – does
not move
It can be positive or
negative
It can be generated by
rubbing two objects
together and removing
“loose” electrons.
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Induction - charge can be
generated by bringing a
touching charged object close
to
another one
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Conduction – charge can be
generated by a charged object
to another object
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Electricity is like water flowing
through pipes
Charge flows when there is a
difference in potential
Current (I) – flow rate (amperes)
Resistance (R) – drag (ohms)
Voltage (V) – force or pressure (volts)
V=IR Voltage = Current X Resistance
SI units
 V = volt = 1 joule/1 coulomb
 I = ampere = 1 coulomb/ second
 R = ohm = 1 volt/amp
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Series Circuit: the components are lined up
along one path. If the circuit is broken, all
components turn off.
R = R1 + R2 + R3 + R4
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Parallel Circuit – there are several branching
paths to the components. If the circuit is
broken at any one branch, only the
components on that branch will turn off.
1/R = 1/R1 + 1/R2 + 1/R3
A grocery store checks the details of a credit
card by having the customer move a
magnetic strip on the card past a wire coil.
Which principle explains this process?
a. An electrical current produces mechanical
energy
b. A permanent magnet produces a changing
magnetic field
c. A changing magnetic field produces an
electrical current
d. Mechanical energy produces a changing
gravitational field
Lisa has a copper wire, a permanent magnet,
and an iron rod. What can she do with these
items to produce an electrical current?
a. Place the wire near the north pole of the
permanent magnet
b. Move the permanent magnet rapidly over
the wire
c. Touch the ends of the wire to the poles of
the magnet
d. Bring the permanent magnet near the end
of the iron rod