Bell Ringer What is work Work Power Machines

Bell Ringer § What is work?

Work, Power, & Machines

What is work ? § The product of the force applied to an object and the distance through which that force is applied.

Is work being done or not? § Mowing the lawn § Weight-lifting § Moving furniture up a flight of stairs § Pushing against a locked door § Swinging a golf club § YES § NO § YES

Calculating Work All or part of the force must act in the direction of the movement. Eureka work

Do you do more work when you finish a job quickly? § Work does NOT involve time, only force and distance. § No work is done when you stand in place holding an object. § Labeling work: w = F x d § Unit of Work: Newton X meter (N m)

The Joule § 1 newton-meter is a quantity known as a joule (J). § Named after British physicist James Prescott Joule.

§ § § How quickly work is done. Amount of work done per unit time. If two people mow two lawns of equal size and one does the job in half the time, who did more work? § Same work. Different power exerted. § POWER = WORK / TIME

The watt § A unit named after Scottish inventor James Watt. § Invented the steam engine. § P = W/t § Joules/second § 1 watt = 1 J/s

watts § Used to measure power of light bulbs and small appliances § An electric bill is measured in k. W/hrs. § 1 kilowatt = 1000 W

Horsepower (hp) = 745. 5 watts § Traditionally associated with engines. (car, motorcycle, lawn-mower) § The term horsepower was developed to quantify power. A strong horse could move a 750 N object one meter in one second. 750 N

Math Review § Work Equation § Power Equation § Work=Force x distance § Power = Work / time To solve for something else use triangle. Cover up what you are solving or looking for and make the equation with what you are given (know).

Math Practice § You must exert a force of 4. 5 N on a book to slide it across the table. If you do 2. 7 J of work in the process, how far have you moved the book?

§ A light bulb does 100 joules of work in 2. 5 seconds. How much power does it have?

§ A man exerts 700 newtons of force to move a piece of furniture 4 meters. If it takes him 2 seconds to move the furniture, how much power does it require? §

§ A hair curling iron uses 13 watts of power. How long must it operate to do 1, 040 joules of work?

§ A 4 -watt night light is left on for 8 hours each night. How much work does it do per night?

§ A force of 100 newtons was necessary to lift a rock. A total of 150 Joules of work was done. How far was the rock lifted?

§ A set of pulleys is used to lift a piano weighing 1, 000 newtons. The piano is lifted 3 meters in 60 seconds. How much power is used?

§ What is the power of a kitchen blender if it can perform 3, 750 joules of work in 15 seconds?

§ A deflated hot-air balloon weighs a total of 8000 N. Filled with hot air the balloon rises to a height of 1000 m. How much work is accomplished by the hot air balloon?

Question? § Give the units for the following measurements: 1. 2. 3. 4. Distance Force Work Power

Machines § A device that makes work easier. § A machine can change the size, the direction, or the distance over which a force acts.

Forces involved: § Input Force § Output Force § FO § FI § Force §Force applied by a applied to machine a machine

Two forces, thus two types of work § Work Input ü work done on a machine =Input force x the distance through which that force acts (input distance) Work and Power video § Work Output ü Work done by a machine =Output force x the distance through which the resistance moves (output distance)

Can you get more work out than you put in? v. Work output can never be greater than work input.

Mechanical Advantage (MA) – expressed in a ratio WITH NO UNITS!! § The number of times a machine multiplies the input force. MA = Fout/Fin

2 types of mechanical advantage § § § IDEAL (IMA) § ACTUAL (AMA) Involves no friction. § Involves friction. IMA =d. E /d. R § E = effort § R = resistance § AMA=FR / FE

Efficiency § Efficiency can never be greater than 100 %. Why? § Some work is always needed to overcome friction. § A percentage comparison of work output to work input. Efficiency(%) = work output (WOut) / work input (WIn) X 100%

Simple Machines Chart – create a 7 x 4 chart titled Simple Machines Machine Description Mechanical Advantage Examples

Simple Machines Gallery Walk § The class will be split into groups. Each group will choose a simple machine and create a poster of that machine. Each poster MUST HAVE the following information: 1. Name of your simple machine 2. Picture or drawing 3. Description of how it works 4. Description of how to determine mechanical advantage 5. Examples and uses in everyday life (you can bring in an example for Extra Credit) § You have 30 minutes to create your poster then we will walk around the gallery to observe the other machines and record the information in your charts.

1. The Lever § A bar that is free to pivot, or move about a fixed point when an input force is applied. § Fulcrum = the pivot point of a lever. § There are three classes of levers based on the positioning of the effort force, resistance force, and fulcrum.

Identify the fulcrum, effort force & resistance force

First Class Levers § Fulcrum is located between the effort and resistance. § Makes work easier by multiplying the effort force AND changing direction. § Examples: IMA = Lin / Lout

Second Class Levers § Resistance is found between the fulcrum and effort force. § Makes work easier by multiplying the effort force, but NOT changing direction. § Examples:

Third Class Levers § Effort force is located between the resistance force and the fulcrum. § Does NOT multiply the effort force, only multiplies the distance. § Examples:

Levers!!!!!!

2. The Wheel and Axle § A lever that rotates in a circle. § A combination of two wheels of different sizes. § Smaller wheel is termed the axle. § IMA = rwheel/raxle.

3. The Inclined Plane § A slanted surface used to raise an object. § Examples: ramps, stairs, ladders § IMA = l(m)/height(m) Can never be less than one.

4. The Wedge § An inclined plane that moves. § Examples: knife, axe, razor blade § Mechanical advantage is increased by sharpening it.

5. The Screw § An inclined plane wrapped around a cylinder. § The closer the threads, the greater the mechanical advantage § Examples: bolts, augers, drill bits

6. The Pulley § A chain, belt , or rope wrapped around a wheel. § Can either change the direction or the amount of effort force § Ex. Flag pole, blinds, stage curtain

Pulley types § FIXED § Can only change the direction of a force. § MA = 1 § MOVABLE § Can multiply an effort force, but cannot change direction. § MA > 1

MA = Count # of ropes that apply an upward force (note the block and tackle!) Fe

§ A combination of two or more simple machines. § Cannot get more work out of a compound machine than is put in.

Physical Science Chapter 16 Thermal Energy & Heat

Physical Science Physics Project n Rube n This Goldberg – Honda Accord Ad Too Shall Pass – Rube Goldberg – State Farm

Thermal Energy Sometimes called internal energy n Depends on the object's mass, temperature, and phase (solid, liquid, gas) n TOTAL potential and kinetic energy of all the particles in an object n

Heat n vs. Temperature The spontaneous flow n A measure of the AVERAGE kinetic of THERMAL energy of the particles from a hot object to a in an object cold object

Let’s compare Temp, Thermal Energy, & Heat!! Temperature – a measure of the AVERAGE kinetic energy of the individual particles of a substance. n Thermal energy – TOTAL energy of all of the particles n Heat – THERMAL energy moving from a warmer object to a cooler object, trying to reach thermodynamic equilibrium. n Which of these can we measure?

Thermal energy vs. temp n Now remember that thermal energy, unlike temperature, depends on mass n Compare a cup of tea and a teapot full of tea, both at the same temperature – Is the average kinetic energy the same in both? § YES! – Which has more thermal energy and why? § The teapot because it has more particles (mass)!

Thermal energy n Which has more thermal energy? – Pitcher of cool lemonade or cup of hot tea? – Pot of boiling water or an iceberg?

Balloon demo Need 2 balloons: 1 filled with air, 1 filled with water Matches Student volunteer

So, how do thermometers work? n Thermal expansion and contraction n Particles move faster and expand as they warm n So, as the temperature increases, the alcohol in the tube expands and its height increases n Heat and temperature - thermometers

Absolute zero- that temperature where the individual particles contain no more energy. The particles (atoms and/or molecules) cease vibrating. No movement occurs. Absolute Zero -459 o -273 o 0 o

Section 16 -1 Review p. 478 In which direction does heat flow on its own spontaneously? n Name 2 variables that affect thermal energy of an object. n Why is it necessary to have regularly spaced gaps between sections of a concrete sidewalk? n

Thermodynamics

Heat Transfer n Heat moves in only one direction: from a warmer object to a cooler object n Two drinks in the same room: n The hot coffee _____ to room temp because. . . n The iced tea _______ to room temp because. . .

– Hot coffee cools to room temp because the heat of the coffee is transferred to the cooler temperature of the room. – A cold glass of Iced tea soon warms up to the surrounding room temperature because the warmer temperature of the room’s surroundings is transferred to the colder glass of iced tea thereby warming it up.

Heat Transfer n Heat is transferred in one of three ways: – Conduction – Convection – Radiation n Specific Heat Video

Conduction n Conduction – heat is transferred from one object to another by direct contact. – Examples include: a metal spoon in hot water gets hot or a pot gets hot as it sits on an electric stove. – Fastest in solids. Much slower in gases. Why? (think about collisions)

Conductors vs. Insulators Conductor – a material that transfers heat well: metal, tile, glass Insulator – a material that does not transfer heat well: air, carpet, wood, wool Conductors vs. Insulators animation Conductors vs. Insulators activity

n Why does a tile floor feel colder than a wood floor, even though they're both at room temperature? – The tile feels colder because it is a better conductor and transfers thermal energy rapidly away from your skin.

n Why does a thick wool sweater keep you warm?

Convection n Convection – the transfer of thermal energy when particles of a fluid move from one place to another…. the particles transfer the heat. – Examples include: a pot of boiling water sets up convection currents to move the hot water at the bottom of the pot being heated to the cooler water at the top of the pot, convection currents in a heated room keep the temperature uniform.

Convection of warm air n Air is heated by sunlight n The temperature of the air – Increases n The air – Expands n The less dense air – Rises n The denser air – Sinks

Radiation n Radiation – transfer of energy by electromagnetic waves. – Examples include: the Sun’s energy traveling through space and heating up the Earth w/out heating space itself, Heat lamps used at fast food restaurants, and the radiator of a car dissipating the heat of an engine.

What type of heat transfer is represented by each arrow?

Heating Systems Central heating systemsuse convection to distribute heat n Radiators-steam, and boilers- water n Put heat into the air it rises, circulates, then falls n Controlled by a bimetallic thermometer n

Cooling Systems Heat pumps- reverse the flow of heat energy Refrigerant- fluid that vaporizes absorbing heat and condenses when giving off heat Must do work to reverse flow of heat energy