agenda: have a great weekend warm up: answer on a separate sheet of paper 1. carla stretches the...
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AGENDA: HAVE A GREAT WEEKEND WARM UP: ANSWER ON A SEPARATE SHEET OF PAPER
1. Carla stretches the rubber band so that it is tight. The stretched rubber band has _________________ energy. 2. When a balloon is blown up it has ______________________ energy. When you let go of the balloon it has ______________________ energy. 3. If a car is on a ramp, how might you increase the amount of potential energy of the car? 4. How does the energy change when a pencil is dropped?
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ELECTRICAL CIRCUITS http://www.brainpop.com/science/energy/electriccircuits/
oDuring the video independently answer your questions.
oYou are silent
oStaying in your seats
oHands are down as we watch
WE ARE WATCHING IT TWICE
Follow along
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ON YOUR NOTES COPY THE DETAILS OF CIRCUITS AND LABEL EVERYTHING YOU SEE Series Circuit-One wire-One loop
Parallel Circuit -Several Loops -If one light goes out, all other lights keep working
Closed Circuit -Electrons flow through an entire loop-Light is on
Open Circuit -Electrons cannot flow through the loop. -The light will not turn on
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WORK: THE USE OF FORCE TO MOVE AN OBJECT OVER SOME DISTANCE W = Fd
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WHICH OF THESE INVOLVES WORK
1. You spend all Saturday trying to lift up your house. It doesn’t move, but you’ve exerted a lot of force.
2. You blow on a piece of paper and it falls off the table.
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W=F X D
Force measured in NewtonsDistance measured in MetersWork measured in Joules (J)
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1. HOW MUCH WORK IS DONE ON A 10 N BLOCK THAT IS LIFTED 5 METERS OFF THE GROUND BY A PULLEY? W = F x d
= 10 N x 5 m
Answer 50 joules
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What do all of these have in common?
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They are all
machines!
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Machine:
Input Force: Output Force:
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Machine: any device that helps
us do work
Input Force: the work you put in to use the machine
Output Force: the work the machine does for you
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What is an advantage?
What advantage does a track team with faster runners have over another team? If you have a greater advantage, the results are more favorable!
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What is mechanical advantage?
The number of times a machine multiplies the input force (the force you use to
make the machine do work).
output force
input forceMA =
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Mechanical Advantage
Example:
If the input force (the force YOU put INTO the machine) is 40 N and the output force (the force of the MACHINE) is 80 N then…
MA = Output force / input force
MA = 80 N MA = ____
40 N
2
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What is efficiency?
Efficiency describes the extent to which time, effort or cost is well used for the intended task or purpose.
Efficiency of a machine relates to work!
Efficiency is how well a machine transfers (converts) the work put in
it.
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Efficiency
An ideal machine would be 100% efficient. Meaning all of the input work would be converted to output work.
This isn’t possible!! Actual machines lose some input work to friction.
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Car vs. Electric Motor
The more moving parts a machine has, the more energy it loses to friction because the parts rub together.
A car engine has an efficiency of only about 25%. It loses much of the energy supplied by its fuel to heat.
A typical electric motor has more than an 80% efficiency. That means the motor converts 80% of the input energy into kinetic energy (motion).
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How can we increase efficiency?
By reducing friction!
How can we reduce friction between the moving parts of a car engine?
Oil! Oil is used to make engines more efficient.
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Ideal Mechanical Advantage vs. Actual Mechanical Advantage Ideal MAis what is desired of a machineassumes no loss of work to friction
Actual MAis what the machine actually does some work is always lost to friction
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PRACTICE WITH YOUR NEIGHBOR -Work with the person to the left or to the right of you
-You must stay in your seats.
-If you have a question, raise your hand
-Pencil in your hand