Day One Intro to Physics and Simple Machines Review Homework Levers, Wheel and Axle, Pulleys Day Two Review Inclined Plane, Wedge, Screw, Agenda
What is a Simple Machine? • A simple machine has few or no moving parts. • Simple machines make work easier
History of Work Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.
Simple Machines Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces. How Pyramids were built?
Early examples that employed simple machines Largest stones ever moved Moving Large Stones Standing up stones How were the pyramids built? Egypt and Mesopotania New Theory on Pyramids Building What are Simple Machines?
Simple Machines • The six simple machines are: • Lever • Wheel and Axle • Pulley • Inclined Plane • Wedge • Screw
Simple Machines • A simple machine is a device that helps make work easier to perform by accomplishing one or more of the following functions: • transferring a force from one place to another, • changing the direction of a force, • increasing the magnitude of a force, or • increasing the distance or speed of a force.
Mechanical Advantage • It is useful to think about a machine in terms of the input force (the force you apply) and the outputforce (force which is applied to the task). • When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.
INPUT FORCE OUTPUT FORCE The farther away from the “Fulcrum” is moved from the “Input Force” the greater the Mechanical Advantage is achieved.
Mechanical Advantage • Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one. • If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10. • In machines that increase distance instead of force, the MA is the ratio of the output distance and input distance. • MA = output/input
INPUT FORCE OUTPUT FORCE 10 lbs 100 lbs MA = OUTPUT / INPUT 100 ÷ 10 = MA OF 10
Simple Machines • Simple Machines can be put together in different ways to make complex machinery
What is work? • In science, the word work has a different meaning than you may be familiar with. • The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.) • The Force must have cause the object to move, otherwise no work was done.
Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • workers pushing a block of stone up and inclined plane
What’s work? The workers are using a force to move the block of stone a distance. Both the force and the motion are in the same direction Motion Force
What’s work? • A scientist delivers a speech to an audience of his peers. • A body builder lifts 350 pounds above his head. • A mother carries her baby from room to room. • A father pushes a baby in a carriage. • A woman carries a 20 kg grocery bag to her car?
What’s work? • A scientist delivers a speech to an audience of his peers. • NO • A body builder lifts 350 pounds above his head. • Yes • A mother carries her baby from room to room. • No • A mother pushes a baby in a carriage. • Yes • A man carries a 20 km grocery bag to his car? • No
a student carrying a book does NO work on the book because the force and motion are NOT in the same direction
Formula for work Work = Force x Distance • The unit of force is newtons • The unit of distance is meters • The unit of work is newton-meters • One newton-meter is equal to one joule • So, the unit of work is a joule
W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?
W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules (W = 20N x 10m)
ANY TIME A MASS IS LIFTED UPWARD, WORK IS DONE. Distance = 5 Meters WORK = (80 n)(5 m) = 400 J Force = 80 Newtons
Power • Power is the rate at which work is done. • Power = Work*/Time *(force x distance) • The unit of power is the watt.
Power = Work*/Time WORK (80 n)(100m) = 8000 JOULES POWER 8000J/40S= 200Watts Motion Force of 80 Newtons Distance is 100 Meters Time is 40 Seconds
Mechanical Advantage – is a ratio of out put to input Work – Force X Distance, Measured in joules Power – Work / Time, Measured in Watts Formulas for simple machines
ARCHIMEDES Lever GIVE ME A PLACE TO STAND AND I WILL MOVE THE EARTH
The Lever • A lever is a rigid bar that rotates around a fixed point called the fulcrum. • The bar may be either straight or curved. • In use, a lever has both an effort (or applied) force and a load (resistant force).
The 3 Classes of Levers • The class of a lever is determined by the location of the effort force and the load relative to the fulcrum.
Levers-First Class • In a first class lever the fulcrum is in the middle and the load and effort is on either side • Think of a see-saw
Levers-Second Class • In a second class lever the fulcrum is at the end, with the load in the middle • Think of a wheelbarrow
Levers-Third Class • In a third class lever the fulcrum is again at the end, but the effort is in the middle • Think of a pair of tweezers
Wheels and Axles • The wheel and axle are a simple machine • The axle is a rod that goes through the wheel which allows the wheel to turn • Gears are a form of wheels and axles
A wheel and axle has a larger wheel (or wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together. When the axle is turned, the wheel moves a greater distance than the axle, but less force is needed to move it. The axle moves a shorter distance, but it takes greater force to move it.Examples: Door Knob, Wagon, Toy Car Wheel and Axle
Pulleys • Pulley are wheels and axles with a groove around the outside • A pulley needs a rope, chain or belt around the groove to make it do work
A pulley is a rope, belt, or chain wrapped around a grooved wheel. Pulleys can be fixed or moveable. The pulley is actually a variation of another simple machine...the lever. A pulley is a circular lever that rotates around its fulcrum. Pulleys
A pulley that is attached to a structure is called afixed pulley. The wheel of a fixed pulley turns, but the pulley itself does not move. A fixed pulley does not multiply the effort force. The distance you apply the effort is the same as the distance the load moves. A fixed pulley changes the direction of effort. When you pull down on the rope, the load moves up. Pulling down is easier than pulling up because you use your body weight when pulling down. Pulleys
Amoveable pulleyis attached to the object you are moving. One end of the rope is attached to a fixed structure overhead. The other end of the rope goes down through the pulley attached to the load and then back up to the top. Pulling on the other end of the rope causes the load to move up. The moveable pulley offers a mechanical advantage even though it does not change the direction of effort. The load is supported by rope on both sides of the pulley, which means that half as much effort is needed to lift the load. You must exert effort twice as far as the load moves. The force needed to move an object is less, but the distance through which the force must move is longer. Pulleys
MA IS EQUAL TO NUMBER OF ROPES SUPPORTING THE MOVABLE PULLEY MA OF 1 MA OF 2 MA OF 3 MA OF 4 SINGLE FIXED SINGLE MOVABLE
Day two *Review Day 1 *Inclined Plane *Wedges *Screws *Gears *Class Activity *Review Day 2
SIMPLE MACHINES, WORK, FORCE, ENERGY & NEWTON'S THREE LAWS OF MOTION • What is a Simple Machine? • A simple machine is any device that transmits the application of a force into useful work. • SIMPLE MACHINES help us make better use of our muscle power to do WORK. • A Machine produces FORCE and controls the direction of Force, it cannot create ENERGY.