Chapter Sections: Section 1- What is Work? Section 1- What is Work? Section 2- Mechanical advantage and Efficiency Section 2- Mechanical advantage and Efficiency Section 3- Simple Machines Section 3- Simple Machines that ’ s all folks …

Work! In science, you do “ work ” on an object if you apply a force on the object which causes it to move some distance as a result.

Work … (cont.) Work cannot take place if there is no motion … Work cannot take place if there is no motion …

Work … (cont.) Work cannot take place if the force is not applied in the same direction as the motion … Work cannot take place if the force is not applied in the same direction as the motion … force motion NO work! motionforce work!

Calculating Work The formula for work is: The formula for work is: Work (J) = Force (N) X Distance (m) Work (J) = Force (N) X Distance (m) A “ Joule ” is the amount of work you do when you exert a force of 1 newton in moving an object a distance of 1 meter.

Calculating Work This weight lifter does 2,400 Joules of work in lifting this barbell 2 meters, how much force is he exerting? This weight lifter does 2,400 Joules of work in lifting this barbell 2 meters, how much force is he exerting?

Calculating Work In rearranging the furniture in your bedroom, you exert a force of 25 N to push your dresser 5 meters. How much work have you done? In rearranging the furniture in your bedroom, you exert a force of 25 N to push your dresser 5 meters. How much work have you done?

What is a Machine? A “ machine ” is any device that makes work easier to do or more effective. A “ machine ” is any device that makes work easier to do or more effective.

Machines … Machines make work easier by: Machines make work easier by: Changing the amount of force you have to exert Changing the amount of force you have to exert Changing the distance over which you exert your force. Changing the distance over which you exert your force. Changing the direction in which you exert your force. Changing the direction in which you exert your force.

Input and Output Force When you do work you ’ re applying a force over some distance. Remember, the work done does not change, so if input force decreases then distance must increase (and vice versa). When you do work you ’ re applying a force over some distance. Remember, the work done does not change, so if input force decreases then distance must increase (and vice versa). Input force: The force you exert on a machine Output force: The force exerted by the machine Input force Output force

Efficiency With any machine, some work is wasted overcoming friction. The efficiency of a machine compares output work to input work. With any machine, some work is wasted overcoming friction. The efficiency of a machine compares output work to input work. Efficiency = output work (J)/ Input work (J) Efficiency = output work (J)/ Input work (J)

Efficiency If Billy exerts a force of 300 N to roll a piano up a 6 meter ramp, what is the efficiency of the ramp if the weight of the piano is 1600 N? If Billy exerts a force of 300 N to roll a piano up a 6 meter ramp, what is the efficiency of the ramp if the weight of the piano is 1600 N? One Meter

Mechanical Advantage A machine ’ s “ mechanical Advantage ” refers to the number of times input force is multiplied by a machine. A machine ’ s “ mechanical Advantage ” refers to the number of times input force is multiplied by a machine. In cases when distance is multiplied, M.A. is less than one. In cases when distance is multiplied, M.A. is less than one.

Mechanical Advantage MA = output force (N) ÷ input force (N) MA = output force (N) ÷ input force (N) Mechanical advantage of 1 or more makes work easier because the output force is greater than the input force ( O > I ) Mechanical advantage of 1 or more makes work easier because the output force is greater than the input force ( O > I ) Mechanical advantage of less than 1 will lower the output force, but can make the distance an object moves longer Mechanical advantage of less than 1 will lower the output force, but can make the distance an object moves longer

Mechanical Efficiency A machines “mechanical efficiency” is a measure of how effective a machine system is. Work output can never be greater than work input because the machine loses some efficiency because of friction A machines “mechanical efficiency” is a measure of how effective a machine system is. Work output can never be greater than work input because the machine loses some efficiency because of friction

Mechanical Efficiency ME = Work Output (J) ÷ Work Input (J) x 100 ME = Work Output (J) ÷ Work Input (J) x 100 Work is never lost, work output + work done to overcome friction is = to the work input Work is never lost, work output + work done to overcome friction is = to the work input Mechanical efficiency can be thought of as a comparison between work input and work output Mechanical efficiency can be thought of as a comparison between work input and work output

Six Basic Simple Machines

Levers “ A rigid bar that is free to pivot or rotate around a fixed point. ” “ A rigid bar that is free to pivot or rotate around a fixed point. ” I.M.A. = distance from fulcrum to input force I.M.A. = distance from fulcrum to input force distance from fulcrum to output force

1 st Class Levers

2 nd Class Levers

3 rd Class Levers

The Pulley “… a grooved wheel with a rope, chain, or cable wrapped around it. ” “… a grooved wheel with a rope, chain, or cable wrapped around it. ” I.M.A.= # of ropes supporting the load I.M.A.= # of ropes supporting the load

Pulleys (cont … ) Fixed Pulley- I.M.A.=1 Pulley System- I.M.A.=4 Moveable Pulley- I.M.A.=2

Challenge Question! What is the I.M.A. of this pulley system? What is the I.M.A. of this pulley system? What do you think the actual mechanical advantage is? What do you think the actual mechanical advantage is? ……………Why? ……………Why?

The Wheel and Axle “… made of two circular objects that are fastened together and rotate about a common axis. ” “… made of two circular objects that are fastened together and rotate about a common axis. ” I.M.A.= Radius of wheel I.M.A.= Radius of wheel Radius of axle

Inclined Plane (ramp) “ A flat slanted surface ” that allows you to exert less force over a longer distance. “ A flat slanted surface ” that allows you to exert less force over a longer distance. The ideal mechanical advantage of an inclines plane is: The ideal mechanical advantage of an inclines plane is: I.M.A.=length of incline/ height of incline I.M.A.=length of incline/ height of incline

2.5 meters 1.25 meters What is the Mechanical advantage?

The Wedge “ A device that is thick at one end and tapers to an edge at another end, ” which multiplies your input force. “ A device that is thick at one end and tapers to an edge at another end, ” which multiplies your input force.

to find the MA (mechanical advantage) of a wedge =length of incline (0.5) height of incline A wedge is a simple machine used to push two objects apart. A wedge is made up of two inclined planes. These planes meet and form a sharp edge. This edge can split things apart.

Double Wedge Single Wedge

A Screw “ A screw can be thought of as an inclined plane wrapped around a cylinder. ” “ A screw can be thought of as an inclined plane wrapped around a cylinder. ”

Threads that are close together make the screw easier to turn, but it takes more turns to move a certain distance. It is faster to fasten a screw with threads that are farther apart, but it takes more effort by the user.

QUIZ! Identify the simple machines in these pictures:

How many simple machines can YOU identify here?

“That’s All Folks!”