Simple Machines

Agenda Day One Intro to Physics and Simple Machines Review Homework Levers, Wheel and Axle, Pulleys Day Two Review Inclined Plane, Wedge, Screw,

Simple Machines

Home work review Provide handout on physics terminology

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?

What are Simple Machines? 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

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?

Mechanical Advantage It is useful to think about a machine in terms of the input force (the force you apply) and the output force (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 COPY THIS SLIDE FOR HAND OUT

INPUT FORCE OUTPUT FORCE 10 lbs 100 lbs MA = OUTPUT / INPUT COPY THIS SLIDE FOR HANDOUT MA = OUTPUT / INPUT 100 ÷ 10 = MA OF 10

Simple Machines Simple Machines can be put together in different ways to make complex machinery

Work and Simple Machines

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? Motion Force 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

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. A man carries a 20 km grocery bag to his car?

a student carrying a book does NO work on the book because the force and motion are NOT in the same direction

Work = Force x Distance Formula for work 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 COPY THIS SLIDE FOR HANDOUT

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) COPY THIS SLIDE FOR HAND OUT

ANY TIME A MASS IS LIFTED UPWARD, WORK IS DONE. Distance = 5 Meters Any time a mass is lifted upward work is done. The force is the weight of the object. 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 POWER (80 n)(100 m) = 8000 JOULES 8000J/40S= 200Watts Motion Force of 80 Newtons Distance is 100 Meters Time is 40 Seconds

Formulas for simple machines Mechanical Advantage – is a ratio of out put to input Work – Force X Distance, Measured in joules Power – Work / Time, Measured in Watts

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

Wheel and Axle

Wheel and axle With wheels and axles the same is true; the movement of the wheel is converted to a shorter but more powerful movement at the axle. The wheel and axle can be thought of as simply a circular lever, as shown in Figure 3.8. Many common items rely on the wheel and axle such as the screwdriver, the steering wheel, the wrench, and the faucet.

Wheel and Axle 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

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

Pulleys 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 a fixed 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. . Examples of a fixed pulley can be found at the top of a flagpole. A person standing on the ground can raise the flag to the top of the pole and lower it to the ground again due to the fixed pulley. You raise and lower your window blinds with a fixed pulley.

Fixed Pulleys . Examples of a fixed pulley can be found at the top of a flagpole. A person standing on the ground can raise the flag to the top of the pole and lower it to the ground again due to the fixed pulley. You raise and lower your window blinds with a fixed pulley.

Pulleys A moveable pulley is 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. . Examples of a fixed pulley can be found at the top of a flagpole. A person standing on the ground can raise the flag to the top of the pole and lower it to the ground again due to the fixed pulley. You raise and lower your window blinds with a fixed pulley.

Moveable Pulleys . Examples of a fixed pulley can be found at the top of a flagpole. A person standing on the ground can raise the flag to the top of the pole and lower it to the ground again due to the fixed pulley. You raise and lower your window blinds with a fixed pulley.

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

Review of day one materials

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.

What is MECHANICAL ADVANTAGE?

INPUT FORCE MA = OUTPUT / INPUT 100 ÷ 10 = MA OF 10 OUTPUT FORCE 10 lbs 100 lbs COPY THIS SLIDE FOR HANDOUT 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.

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 caused the object to move, otherwise no work was done.

Work = Force x Distance Formula for work 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 COPY THIS SLIDE FOR HANDOUT

What Is 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 POWER (80 n)(100 m) = 8000 JOULES 8000J/40S= 200Watts Motion Force of 80 Newtons Distance is 100 Meters Time is 40 Seconds

Inclined Planes An inclined plane is a flat surface that is higher on one end Inclined planes make the work of moving things easier How were the Pyramids built? A sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed. You can use this machine to move an object to a lower or higher place.  Inclined planes make the work of moving things easier.  You would need less energy and force to move objects with an inclined plane.  http://www.archaeology.org/0705/etc/pyramid.html

Inclined plane & friction Friction is opposition to motion, so if nothing is trying to move there will be no friction. However, friction will be present when motion is attempted, even if the object is not yet moving. There are two different types of friction: static, which acts before the object begins to move, and dynamic, which acts after the object begins moving. Static friction is usually stronger than dynamic friction.

Inclined plane

Inclined plane . An inclined plane is a flat surface set at an angle (other than a right angle) against a horizontal surface. An inclined plane is a simple machine with no moving parts. It is simply a straight slanted surface. Some examples of an inclined plane are the playground slide, steps, a ski jump, and a wheelchair ramp

Inclined plane The inclined plane permits you to overcome a large resistance by applying a relatively small force through a longer distance than the load is to be raised. The steeper the slant, the more work it takes to go up the inclined plane. As the slant of an inclined plane decreases, the mechanical advantage increases. It takes less force to raise the object, but the object must move through a longer distance

Inclined plane mechanical advantage To find the MA of an inclined plane, divide its length by its height. MA = length / height 600/100 = 6 MA 600 METERS LENGTH 100 METERS HEIGHT

Inclined plane work To find the WORK of an inclined plane, WORK = Force X Distance 600/100 = 6 MA 50n X 600m = 30,000 Joules 600 METERS LENGTH 100 METERS HEIGHT 50n

Wedges Two inclined planes joined back to back. Wedges are used to split things.

Wedges A wedge uses force to come between two things. A wedge is used for three different types of work: connecting (the nail), splitting (the ax), and tightening (the doorstop.) One end of the wedge tapers to a thin edge and the other end is wide. The longer and thinner a wedge is, the less effort is needed to overcome the resistance force. A very sharp knife requires less effort to cut through a potato because it's blade has been made thinner by sharpening. Try hammering a very thin nail into a block of wood and then try hammering a thick nail into the same block of wood. Which was easier? The thin nail is easier to hammer into the wood because the point of the nail (the wedge) is thinner. INTRO - When you use an inclined plane to do work the inclined plane stays still and the object being acted upon is moving. When using the wedge, the object being acted upon stays still and the wedge is moving. A very sharp knife requires less effort to cut through a potato because it's blade has been made thinner by sharpening. LAST - Try hammering a very thin nail into a block of wood and then try hammering a thick nail into the same block of wood. Which was easier? The thin nail is easier to hammer into the wood because the point of the nail (the wedge) is thinner.

Wedges Inclined planes are commonly put to use in cutting devices and often two inclined planes are put back to back to form a wedge. In a wedge forward movement is converted into a parting movement acting perpendicular to the face of the blade (see Figure 3.6). A zipper is simply a combination of two lower wedges for closing and an upper wedge for opening

Screws A screw is an inclined plane wrapped around a shaft or cylinder. The inclined plane allows the screw to move itself when rotated.

screw

screw Screws are designed to change the direction of effort. The screw's threads move objects up or down as the screw turns. When you turn a screw into a piece of wood in a circle with a screwdriver the screw goes down into the wood. Circular motion is turned into forward motion. This is how a fan creates a current of air to cool you off on a hot day. The blades of your fan are also a type of screw. An inclined plane makes work easier by allowing the work to be done over a longer distance. So does a screw! The closer together the threads of a screw are, the longer the distance over which the effort is exerted, and the more the force is multiplied. Examples of a screw include the lid of your jar of peanut butter, the jack you lift the car with when changing a tire, and airplane propellers.

gears

Spur Gears

Helical gears

Bevel gears

Worm gear

Gear ratio Count the gear teeth to determine exact gear ratios - you just count the number of teeth in the two gears and divide. So if one gear has 60 teeth and another has 20, the gear ratio when these two gears are connected together is 3:1.

Gear rotation When two gears of unequal number of teeth are combined a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship.

Multi gear rotation

review Class activity – In groups find examples of class I, II, and III levers Research how to find the MA of an inclined plane that is 100 meters (L) x 20 meters (H) Complete the Simple Machines Work Sheet

Power = Work*/Time WORK POWER (60 n)(200 m) = 12000 JOULES 12000J/80S= 150 Watts MECHANICAL ADVANTAGE 200/25=8 MA Motion Force of 60 Newtons HEIGHT IS 25 M Distance is 200 Meters Time is 80 Seconds

B A C Gear “B” is rotating “counter clock” wise