January 06, 2017

Chapter 14:

Simple Machines, MA, & Efficiency

January 06, 2017

What is a simple machine?

A simple machine is a machine that does work with only one movement of that machine. There are 6 basic simple machines:

1) Lever 2) Wheel & Axle 3) Screw

4) Inclined Plane 5) Pulley 6) Wedge

Leveris a stiff bar that rests on a support called a fulcrum which lifts or moves a load

Ideal Mechanical Advantage of Lever:

IMA = Length of Input Arm (m)Length of Output Arm (m)

IMA =LinLout

IMA formula

January 06, 2017

LeversA Lever is a bar that is free to pivot around a fixed point.

There are three types of levers:

First Class Lever

In a first class lever, the fulcrum if found in between the input force and output force (load)

The closer to the fulcrum you apply the force, the more effort you need to lift up the resistance and vice versa.

The output goes in the opposite direction of the input.

If a person pushes down, the output goes up, and if a person pushes up, the output goes down.

A see-saw is an example.

January 06, 2017

Second Class LeverA wheel barrow is an example.

A second class lever is a lever in which the output is located between the fulcrum and the input.

**A second class lever always increases the input force.

The fulcrum is the wheel and output in a wheelbarrow is the object being moved while the person pushing the wheelbarrow supplies the input.

Third Class Lever

**A third class lever always decreases the effort force.

The input is between the output and the fulcrum.

The fulcrum is the elbow, the biceps provide the resistance and the effort is whatever is being lifted.

The distance from the elbow to the biceps is the input arm and the distance from the elbow to whatever one is trying to lift is the output arm.

A third class lever is always a disadvantage.

An example is a person's arm.

January 06, 2017

Let's Practice:John uses a lever to lift a weight of 5 N. The input distance (where the input force is applied) is 50 cm. The output distance (where the output force is applied) is 5 cm. What is the ideal mechanical advantage of the lever? IMA = input distanceof lever output distance

Know Input distance = 50 cm; output distance = 5 cm

Setup

Solve

IMA = 50 cm5 cm

IMA = 10

Let's Practice:

Know Input distance = 5 m; output distance = 2.5 m

Setup

Solve

IMA = 5 cm2.5 cm

IMA = 2

Howard uses a pulley system to raise a bucket from a well. He pulls his end on the rope 5 m and the bucket is raised 2.5 m. What is the ideal mechanical advantage of this pulley system?

IMA= input distance output distance

January 06, 2017

Wheel and Axle

a wheel with a rod through its center lifts or moves loads; the rod is called an axle

a wheel and axle helps a bicycle to move

Wheel and Axle

a wheel with a rod through its center lifts or moves loads; the rod is called an axle

Ideal Mechanical Advantage of Wheel and Axle:

IMA = Radius of wheel (m)Radius of axle (m)

IMA =rwra

IMA formula

January 06, 2017

Let's PracticeWhen making mousetrap cars, wheels are very important, some wheels are larger than others. Pretend one car has the following measurements for their wheels: the radius axle (the small wheel) measured only 1 cm. The radius of the larger wheel (the one that touched the pavement) measured a whopping 10cm. What was the mechanical advantage of these large wheels?

Formula: IMA = Radius wheel (rw)Radius axle (ra)

solve

setup IMA = 10 cm1 cm

IMA = 10** this means with each turn of the axle you get 10 times the distance

Screw

is an inclined plane that is wrapped around a pole which holds things together or lifts materials

screw threads on the top of a jarkeep the lid on tight

January 06, 2017

Screw

is an inclined plane that is wrapped around a pole which holds things together or lifts materials

The IMA is larger if the thread are closer together. However, if there are more threads it takes longer to drive the screw into the material.

Inclined Planea slanted surface used to help move an object up or down

a driveway ramp moves cars over the curb

January 06, 2017

Inclined Planea slanted surface used to help move an object up or down

IMA of an Inclined Plane:

IMA = length of slope (m)height of slope (m)

IMA= Lh

IMAFormula

Let's PracticeYou got roped into helping your parents' friend move. You are loading some pretty heavy boxes, but luckily they have a ramp on the back of the truck. The truck is 1.5 meters off the ground and the ramp is 6 meters long. What is the IMA of this ramp?

IMA = length of slopeheight of slope

solve

setup IMA = 6 m1.5m

IMA = 4

January 06, 2017

Pulley - a rope that fits into a groove in a wheel.- may be fixed, movable, or a pulley system

a window blind is raised and lowered with a pulley

Pulley - a rope that fits into a groove in a wheel.- may be fixed, movable, or a pulley system

The IMA of a pulley system is equal to the number of rope segments that support the weight.

January 06, 2017

Wedge

is an object with at least one slanting side ending in a sharp edge,which cuts material apart

a chisel is a wedge used to split logs or wood

Wedge

is an object with at least one slanting side ending in a sharp edge,which cuts material apart

The thinner the wedge, the greater the IMA.

IMA = Length of WedgeWidth of Wedge

January 06, 2017

What simple machines make up a hand truck?

lever

inclined plane

1. wheel and axle

2.

3.

What simple machines do you find in a stapler?

lever

wedge (staple)

January 06, 2017

Mechanical AdvantageThe number of times that the machine increases the input force is the mechanical advantage.

Ideal Mechanical advantage is the mechanical advantage of a machine without friction.

FormulaIMA = Input DistanceOutput Distance

IMA is the relationship of the distances.

Mechanical AdvantageThe number of times that the machine increases the input force is the mechanical advantage.

Actual Mechanical advantage is the mechanical advantage of a machine with friction.

FormulaAMA = Output Force Input Force

AMA is the relationship of the forces.

January 06, 2017

Efficiency

Erase the colored box to reveal the efficiency formulas.

Efficiency is the comparison of work output to work input. It measures the amount of work that went into a machine that is changed to useful output work. It is expressed as a percent.

Calculate the efficiency of this ramp.

Tap the image. Drag and drop the numbers from the story problem into the equation.

A worker uses 600N of force to push a 1000N piano up a 5 meter long ramp that rises 2 meter high.

Efficiency Formulae = [(F out x d out) / (F in x d in)] x 100

HINT

N = Newton Named after Sir Isaac Newton, this unit of force is equal to the amount of force required to accelerate one kilogram at one meter per second squared. 1N = (kg * m) / s2

January 06, 2017

Calculate the efficiency of this pulley system.

Tap the image. Drag and drop the numbers from the story problem into the equation.

A worker expends 120J of energy to move 90J on a pulley system.

Efficiency Formulae = (W out) / (W in) x 100

HINT

J = Joule Named after James Prescott Joule, this unit of energy is equal to expending a force of one Newton through

a distance of one meter. 1J = 1N * m

Why can’t a machine operate at 100% efficiency?

Many attempts have been made at creating a machine that runs at 100% efficiency.

Use the pen to write your answers. Erase each line to reveal other examples.

Heat lossEnergy used by other parts of the machine (oil/water pump, air conditioner, etc..)Friction of moving partsAir dragImperfect timingDesign compromises (low emissions, low noise, fast starting, etc..)Idiling

1)2)

3)4) 5) 6)

7)

Write your answers here:

January 06, 2017

How efficient is it?

Try to match the machine with its efficiency.

How can efficiency be increased?

Match problem with a solution.

January 06, 2017