Week 15

Monday Warm UpWeek 15

What is work?

Cornell Notes: Work and Simple Machines

Work: the transfer of energy to an object by using a force that causes the object to move in the direction of the work.

Movement in direction of force.

How do you know if it is work?

1. the object moves as force is applied2. the object moves in the same direction as the force

Ex: carry a backpack (force up, motion forward) not work. lifting a bag (force up, motion up) is work.

How do you calculate work?

Work = Force x distance W = F x d

Force in NewtonsDistance in meters

What is the unit to measure work?

Joule (J)

Work is a transfer of energy, joules measure energy.

What is power?

Power is the rate at which work is done.

Power = Work divided by time (P = W/t)

Measured in Watts (W)

What is a machine?

A device that helps do work byovercoming a force

or changing direction of applied force

What is work input?

Work input is the amount of work you do on the machine.

Work input is force x distance you put into machine.

What is work output?

Work output is the work done by the machine.

Work output = Force x distance of output.

How do machines help?

1. They DO NOT increase amount of work done.2. They DO allow force to be applied over greater distance which means less force is needed to do same work.

Let's find all the ways to get 12 J of work:Force Distance12 16 24 33 42 61 12

As force decreases, distance increases but work stays the same.

What is mechanical advantage?

Some machines make work easier by increasing force or giving it a mechanical advantage.

Mechanical advantage is the number of times a machine multiples force.

How do you calculate mechanical advantage?

mechanical advantage = output force divided by input force.

MA = output/input

Thought check:

If you had to push a 500 N weight up a ramp and only needed to push with 50 N of force, what is the mechanical advantage of the ramp?

What is mechanical efficiency?

The ratio of work output to work input is the mechanical efficiency.

Work Output is always less than work input because the machine has to overcome friction.

How do you calculate mechanical efficiency?

mechanical efficiency = work output/work input x 100

The ME is expressed as a percentage.

A perfect machine would be 100% efficient.

Assignment

Do page 221 #1-10

Tuesday Warm UpWeek 15

Suppose you exert 60 N on a machine and the machine exerts 240 N on another object. What is the machine's mechanical advantage?

MA = output/input

Cornell notes: Simple machines

Content/writing space

What are the six simple machines?

LeversPulleysWheel and axleInclined PlaneWedgeScrew

Lever: A machine that has a bar that pivots at a fixed point called a fulcrum.

Input force

Output force

Three types of levers:

First class lever: fulcrum in middleSecond class lever: Output force (load) in middleThird class lever: Input force (effort) in middle

Lever's Mechanical Advantage:MA = output force/input force

Second class lever MA > 1 (load close to fulcrum)

Third class lever MA < 1 (force decreased but over longer distance)

First class lever MA depends upon location of fulcrum.

Pulley: machine that consists of a wheel over which a rope passes.

Fixed PulleyMovable Pulley

Block and Tackle

Mechanical Advantage of Pulley

Fixed: MA = 1Movable: MA = 2Block & Tackle: MA = # rope segments on load

Wheel & Axle

A machine with two circular objects of different sizes, the wheel is larger than the axle.

Mechanical Advantage of Wheel & Axle

MA - radius of wheel divided by radius of axle.

Inclined plane: a machine that is a straight, slanted surface - a ramp.

Mechanical Advantage of Inclined plane:

MA = length divided by height

Wedge: a machine made up of two inclined planes that moves - often used for cutting.

Mechanical Advantage of wedge:

MA = length divided by greatest thickness

Screw: machine that consists of an inclined plane wrapped around a cylinder.

Mechanical Advantage of a Screw:

MA = length of ramp divided by height (just like the inclined plane it would be if you unwrapped it).

Compound machine

Two or more simple machines together.

Assignment

Do page 229 #1-9

Wednesday Warm UpWeek 15

A wheelchair ramp is 5.6 m long and 0.8 m high. What is the ramp's mechanical advantage?

MA = length/height

Assignment

www.explorelearning.comAnts on a Slant gizmo and pulley gizmo

Do worksheets and take assessments

Thursday Warm UpWeek 15

If a wheel has a radius of 12.5 cm and an axle has a radius of 0.5 cm, what is the mechanical advantage of the wheel and axle?

MA = radius of wheel/radius of axle.

Assignment

www.explorelearning.comLever gizmo and Wheel & Axle gizmo

Complete worksheets and take assessments.

Friday Warm UpWeek 15

What is the mechanical advantage of this block and tackle system?

Video: Simple Machines

Complete the worksheet as the video plays.