2What is Work?Work is done when a force is exerted on an object and causes it to move in the same direction the force was exerted.Force – a push or pull
3The amount of work you do is not affected by how fast or slow you do the work. If you carry a backpack up a flight of stairs, you are still carrying the same amount of weight over the same amount of distance. Time is not a factor in work.
4Calculate Work Work (W) = Force(F) x Distance(D) W = F x D Force is measured in Newtons (N)Distance is measured in meters (m)So, Work is measured in N*m or Joules (J)
5What is a Joule?A joule is the amount of work you do when you exert a force of 1 Newton to move an object a distance of 1 meter.
6If a 50N force was exerted lifting a plant and carrying it a distance of 0.5m, how much work was done?W = ?W = F x DF = 50ND = 0.5m
7W = F x DW = (50N) (0.5m)W = 25 N*mOR25 Joules (J)
9What is Power?Power is the RATE at which work is done.Rate = Time
10Calculating Power Power(P) = Work(W) / time(t) P = W/t P = Force x Distance / timeWork is measured in Joules (J)Time is measured in seconds (s)Power is measure in J/sJ/s = Watts
11A tow truck exerts a force of 11,000N to pull a car out of a ditch A tow truck exerts a force of 11,000N to pull a car out of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck?P = ?P = F x D / t OR P = W/tF = 11,000 ND = 5 mt = 25 s
12P = 11,000 N x 5 m / 25 s P = 55,000Nxm(J) / 25 s P = 2,200 J/s OR watts
13A watt is a relatively small unit of power. One kilowatt (kW) = 1,000 watts (W)One horsepower = 746 watts
14How Machines Do Work? What is a Machine? A machine allows you to do work easier or more effective.HOW?
153 ways in which a machine can make work easier. A machine may change the amount of force you exert. By taking some of the force away from you.The distance over which you exert your force.Or their direction in which you exert your force.
16Remember that in order for work to be done a force must be applied. You have an input force and an output force
17Input force/Output force The force you exert on the machine – input force.The machine in turn applies the force to the object – Output forceThe distance the machine moves after the input force is applied - input distanceOutput distance – the machine exerts a force over another distance, distance object moves
21Mechanical AdvantageThe number of times a machine increases a force exerted on it.Mechanical advantage = output force/ input forceMA = Fo / Fi
22Calculating Mechanical Advantage What is the MA if the input force of 10N is exerted on a hand-held can opener, and the opener exerts an output force of 30N?MA = ?MA = output force / input forceOutput force = 30NInput force = 10N
23MA = 30N / 10NMA = 3The can opener triples your input force.
24Are machines actually efficient? Efficiency – compares the output work to the input work. Efficiency is expressed as a percent. The higher the percent the more efficient the machine.
25Calculating Efficiency Efficiency = Output Work / Input Work x 100%Eff = Wo / Wi Multiplied by 100%We multiply because we end up with a decimal, so we move out decimal two places to the right.
26Example efficiencyYou do 250,000 J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower?Efficiency = ?Eff = output work / input work x 100%Work input = 250,000 JWork output = 200,000 J
27Eff = 200,000J / 250,000J x 100% .8 x 100% eff = 80%
28What would your ideal efficiency of a machine be? 100% efficient
29Simple MachinesInclined planeScrewleverWedgePulleyWheel and axle
30What is a simple machine? Remember a machine makes work easier by changing the force, the direction, or the distance the force is applies.
311. Inclined Plane A flat, sloped surface Allows you to exert your input force over a longer distance.As a result the input force needed is less than the output forceIdeal MA = Length of incline / height of incline
471. A fork is an example of a:pulley wedge wheel and axle 2. A bicycle is an example of a: wheel and axle wedge lever 3. A bathtub is an example of a/an: pulley screw inclined plane 4. A swivel chair is an example of a: lever screw wedge 5. A teeter totter on the playground is a: lever inclined plane pulley 6. You would use a pulley to: cut food hold pieces of wood together help open and close venetian blinds
48Simple Machines and the Human Body ElbowNeckAnkleWedges/mouth
49Compound MachinesA machine that utilizes two or more simple machines.
50Homework You are to make a foldable List all 6 simple machines For each machine show a picture and give its definitionYou will need 4 halves sheets of paper