TAKS Objective 5
description
Transcript of TAKS Objective 5
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TAKS Objective 5
The student will demonstrate an understanding of motion, forces,
and energy.
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Practice filling in
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• Speed is the rate of change in position
• V = d t
– V = velocity– d = distance– t = time
Speed
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V = d t
Set up the Speed Triangle
d
tv
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v = v = dd
tt
Sometimes the question will use the word VELOCITYVELOCITY instead of speed.
A 1-kilogram ball travels 50 meters in 5 seconds. The velocity of the ball is —
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Exit 2009
Speed = 56 meters 96 sec
Speed = 0.58 m/s
d
tv
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• Velocity is the speed and direction of an object
• The velocity of an object can change even if the speed remains constant
Velocity & Speed
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• Acceleration is the rate of change of velocity–Speeding up –Slowing down
Acceleration
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vf - vi
a = -------- t
vf = final velocity
vi = initial (beginning velocity)
a = accelerationt = time
Equation to find Acceleration
vf - vi
ta
vf - vi
a
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Grade 10 2009
a = (30 m/s) – (20 m/s)2 seconds
a = (10 m/s) 2 s
a = 5 m/s2
t
vf - vi
a
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• Forces are all around us– Pushing– Pulling– Squeezing
What is a force?
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• Momentum can be defined as "mass in motion.”
• Momentum depends upon the variables mass and velocity
• Momentum = mass x velocity • p = m x v
– m = mass– v = velocity– p = momentum
Momentum
p
vm
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• Describe the momentum of a 5-kg bowling ball moving westward at 2 m/s.
• p = m x v• p = 5 kg x 2 m/s• p = 10 kg x m/ s
Momentum
p
vm
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Grade 10 2009
p = mvp = 2.0 kg x 15 m/sp = 30 kg • m/s
p
vm
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p = m x vp = 0.2 kg x 12 m/sp = 2.4 kg • m/s
Exit 2009
p
vm
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Energy is the amount of work a physical system is capable of
performing.
The Law of Conservation of Mass states:
Energy can neither be created nor destroyed
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A measure of the change a force produces.
The work done by a force acting on an object is equal to the force multiplied by the distance through which the force acts.
FdW W
dF
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Work is done……by a force when the object it
acts on moves a distance
NO work is done by pushing against a wall that will not move.
Work IS done throwing a ball because the ball MOVES while being pushed during the throw.
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joule (J) The SI unit of energy
Amount of work done by a force of one Newton when it acts through a distance of one meter:
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PRACTICE PROBLEM #1PRACTICE PROBLEM #1
A person pushes a large box across a level floor by applying a horizontal force of 200 N. If the person pushes the box a distance of 5 meters in 10 seconds, how much work does the person do on the box?
A 2000 joules
B 1000 joules
C 400 joules
D 100 joules
Work =force x distance
W=F x dW= (200N)(5m) = 1000 joules
W
dF
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The weight lifter used a force of 980 N to raise the barbell over her head in 5.21 seconds. Approximately how much work did she do in raising the barbell?
F 380 JG 982 JH 2,000 JJ 10,000 J
(Practice problem from TEA released TAKS Test)
W=F x dW= 980N x 2.04m =1999.2J
W
dF
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The RATE of Doing Work… Power is the amount of work done in a
specified period of time The more powerful something is, the faster it
can do work
time
WorkPower W
tP
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A mechanic used a hydraulic lift to raise a12,054 N car 1.89 m above the floor of agarage. It took 4.75 s to raise the car.
Whatwas the power output of the lift?A 489WB 1815WC 4796D 30,294W
(Practice problem from TEA released TAKS Test)
P=W / tW = F x d W=12,054N x 1.89m = 22,782.06J
P= 22,782.06J/4.75s=4,796.2W
W
tP
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Day 2Day 2Newton’s Three Laws, Simple Machines, & Waves
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11stst Law of Motion Law of Motion (Law of Inertia) (Law of Inertia)
An object at rest will stay at rest, and an object in motion will stay in motion, unless acted upon by an unbalanced force.
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11stst Law Law Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.
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What is one type of What is one type of unbalanced force that unbalanced force that acts on an object in acts on an object in motion?motion?
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FrictionFrictionSlide a book
across a table and watch it slide to a rest position. The
book comes to a rest because of
friction.
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Newton’s 1Newton’s 1stst Law and You Law and You
Don’t let this be you. Wear seat belts.
Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving forward at 80 km/hour.
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Grade 10 2009
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22ndnd Law Law
The force of an object is equal to the product of
its mass and acceleration, or
F=m x a.
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22ndnd Law Law
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22ndnd Law Law
How much force is needed to accelerate a 1400 kilogram car 2 m/sec2?
F = m x a
F = 1400 kg x 2 m/sec2
2800 NF
am
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Check Your UnderstandingCheck Your Understanding
1. What acceleration will result when a 12 N net force is applied to a 3 kg object?
F = m x a
a = F = 12 N = 4 m/sec2
m 3 kg
F
am
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Check Your UnderstandingCheck Your Understanding
2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2.
Determine the mass.
F = m x a
m = F = 16 N = 3.2 kg a 5 m/s2 F
am
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Check Your UnderstandingCheck Your Understanding
3. How much force is needed to accelerate a 66 kg skier 1 m/sec2?
F = m x a
F = 66 kg x 1 m/sec2 F
am
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Check Your UnderstandingCheck Your Understanding
4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec2?
F
am
F = m x a
F = 1000 kg x 9.8 m/sec2
F = 9800 NF
m
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F = (6.0 kg) x (0.50 m/s2)
F = 3 kg • m/s2
W = (3 kg•m/s2) x (8.0 m)
W = 24 Nm
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33rdrd Law LawFor every action, there is an equal and opposite reaction.
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33rdrd Law LawWhen you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.
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33rdrd Law Law
The hot gases The hot gases push down push down against the against the
ground. As the ground. As the gases move gases move
downward, the downward, the rocket moves in rocket moves in
the opposite the opposite direction, direction, upward.upward.
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Exit 2009
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Exit 2009
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What is a Simple Machine? A simple
machine has few or no moving parts.
Simple machines make work easier
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Wheels and Axles
The axle is a rod that goes through the wheel which allows the wheel to turn
Gears are a form of wheels and axles
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Pulleys
Pulley are wheels and axles with a groove around the outside
A pulley needs a rope, chain or belt around the groove to make it do work
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Inclined Planes
An inclined plane is a flat surface that is higher on one end
Inclined planes make the work of moving things easier
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Wedges
Two inclined planes joined back to back.
Wedges are used to split things.
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Screws
A screw is an inclined plane wrapped around a shaft or cylinder.
The inclined plane allows the screw to move itself when rotated.
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Levers-First Class
In a first class lever the fulcrum is in the middle and the load and effort is on either side
Think of a see-saw
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Levers-Second Class
In a second class lever the fulcrum is at the end, with the load in the middle
Think of a wheelbarrow
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Levers-Third Class
In a third class lever the fulcrum is again at the end, but the effort is in the middle
Think of a pair of tweezers
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There are also two kinds of work to be considered when a machine is used. Work done on the machine – Win (work
input) Work done by the machine – Wout (work
output)
You can never get more work out of a machine than you put in.
Wout can never be greater than Win
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Mechanical Advantage
The number of times a machine multiplies the effort force is the mechanical advantage (MA) of the machine.
MA = work output work input
wo
wiMA
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Efficiency
Efficiency is a measure of how much of the work put into a machine is changed to useful work put out by a machine.
The higher the efficiency, the greater amount of work input that is changed to work output.
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600 N x 2.5 m = 1500 Nm
300 N x 6.5 m = 1950 Nm
1500 Nm 1950 Nm
X 100 = 77%
Exit 2009
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WAVESWAVES
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A transverse wave is a wave in which the particles of the medium move in a 90 degree angle to the direction of energy transport.
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The crest of a wave is the highest point of the wave.
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The trough of a wave is the lowest point of the wave.
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The amplitude of a wave refers to the amount of energy carried by a wave.
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A longitudinal (compressional) wave is a wave that moves in the same direction as
the medium it is traveling through.
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Wavelength – the distance from a point in a wave to the next point that wave in the same place.****From crest to crest or trough to trough
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• Frequency – the number of complete waves passing a point per second
How many cars pass the line in one second?
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By knowing the frequency of a wave and its wavelength, we can find its velocity.
Here is the equation for the velocity of a wave:
velocity = wavelength x frequency or
v = x f
f
v
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Wave Properties: Reflection
When a wave hits a barrier, it will be reflected depending on the direction of the barrier (normal).
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• Refraction causes objects to appear in a different place than it actually is because when light passes into a different medium the light path bends.
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Wave Properties: InterferenceWhen two waves travel through the same medium and collide.
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1. Constructive interference is when the amplitudes of the initial waves are in the same direction. The resulting wave will be larger than the original waves.
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Constructive Interference
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2. Destructive interference is when the amplitudes of the initial waves are opposite.
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Destructive Interference
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Exit 2009
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Wave Properties: Resonance
• Resonance - VIBRATIONS.
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Grade 10 2009
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Energy, Heat & Circuits
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Types of Energy
Kinetic – Energy of Motion Potential – Energy of Position
Chemical Energy Food converted to energy in our bodies
Heat Energy Heat from burning oil to make steam to drive turbines
Electric Energy Electricity turns motors in homes and factories
Radiant Energy Energy from the sun
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Kinetic Energy
Kinetic energy = the energy an object possesses due to its motion
Kinetic energy = ½ mv2
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Kinetic Energy
Kinetic energy of a 1000kg car moving at 10 m/s is 50kJ
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Potential Energy
Energy stored in an object.
Gravitational Potential EnergyWhen a stone is dropped, it falls towards
the ground, until it hits the ground
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Potential Energy Gravitational Potential energy =
the energy an object possesses because of its position relative to the ground
h mg
Gravitational
Potential = mgh Energy
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Potential Energy Example Potential energy of a car pushed
off a 45m cliff
kJmsmkgmghPE 441)45)(/8.9)(1000( 2
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Conservation of Energy
Law of Conservation of Energy:Energy cannot be created nor
destroyed, although it can be changed from one form to another.
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Exit 2009
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Temperature and Heat
Thermal energy: the total potential and kinetic energy of the particles of a material.
Heat is thermal energy in motion.
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Methods of Heat Energy Transfer Conduction is the transfer of heat energy by
direct contact Convection is the transfer of heat energy by
the movement of fluids(gas or liquid) currents.
Radiation is the transfer of heat energy by electromagnetic waves
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A. Conduction transfers energy as heat along the wire and into the hand
B. Embers swirl upward in the convection currents that are created by the warmed air above the fire which rises
C. Electromagnetic waves emitted by the hot campfire transfer energy by radiation
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Heat Transfer by Conduction
Conduction is the transfer of thermal energy by direct contact of an object to a heat source.
When a metal poker is put in a hot fire, the exposed end of the poker soon becomes hot as well. We say that heat has been conducted from the hot end to the cold end.
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Heat Transfer by Convection Convection is the process
of heat transfer through the mass motion or flow of some fluid, such as air or water. When a pot of water is heated,
convection currents are set up as the heated water at the bottom of the pot rises because of its reduced density and is replaced by cooler water from above.
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Heat Transfer by Radiation
Radiation is a more rapid transfer of thermal energy in the form of electromagnetic radiation. The warmth you fell when you warm yourself
by a fire is due to this radiation. If the object is hot enough, some of the radiation is visible and can indeed be seen.
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What type of heat transfer is shown in the following pictures?
A.
B.
C.
D.
Convection
Radiation
Radiation
Conduction
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Grade 10 2009
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Exit 2009
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Conductors and Insulators
Conductors readily transfer heat energy.
Insulators are poor conductors of heat energy.
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Exit 2009
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Exit 2009
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CircuitsCircuits
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Circuit DiagramsCircuit DiagramsA circuit diagram is a drawing of a real circuit, allowing you to see the direction of flow of electricity.
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Basic Parts of a CircuitBasic Parts of a CircuitSwitch – can be used to turn
circuits on and offWires – for the current to run
throughPower Source – for example a
battery
Switch
Battery
Wires
Light Bulb
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Open & Closed CircuitsOpen & Closed CircuitsWhen a circuit is turned off, it is
called an open circuit, because it has a break in it or the switch is open.
When there are no longer any breaks in the circuit, it is called a closed circuit, and the electricity will flow through the circuit.
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Open CircuitOpen Circuit
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Closed CircuitClosed Circuit
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Two Types of CircuitsTwo Types of Circuits1. Series Circuit
2. Parallel Circuit
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Series CircuitSeries CircuitIn a series circuit, the current can
only take one path.All the current flows through
every part of the circuit.◦Christmas Lights – if you remove one
bulb and the whole strand goes out, then they were made in series.
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Series CircuitSeries Circuit
Only one path to follow!
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Parallel CircuitsParallel Circuits
In parallel circuits, the current can take more than one path. ◦The electrical circuits in homes and buildings are parallel circuits
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Parallel CircuitParallel Circuit
MORE than one path to follow (THREE)!
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2009 Grade 10
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CurrentCurrent
Current is the flow of electrical charges.
Current is measured in amperes.
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ResistanceResistance
Resistance (R) is a measure of how difficult it is for the charges to flow through the wire.
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Ohm’s LawOhm’s LawOhm’s Law states that the
current of a circuit is the ratio of the voltage and the resistance of the circuit.
I = V / R◦I = current (amps)◦V = voltage (volts)◦R = resistance (ohms)
V
RI
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Practice ProblemPractice Problem
In this circuit, how much current flows through the light bulb?
A 0.75 ampB 1.50 ampsC 2.0 ampsD 3.0 amps
CurrenCurrentt = = voltage voltage = = V V resistance R resistance R
Current = Current = 1.5 volts1.5 volts = = 0.75 0.75 ampamp
2.0 ohms 2.0 ohms