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?

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

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

WORK: THE USE OF FORCE TO MOVE AN OBJECT OVER SOME DISTANCE W = Fd

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.

W=F X D

Force measured in NewtonsDistance measured in MetersWork measured in Joules (J)

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

What do all of these have in common?

They are all

machines!

Machine:

Input Force: Output Force:

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

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!

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 =

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

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.

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.

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).

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.

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

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