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“Work and Simple Machines”

Lever Pulley Wheel and Axle

Wedge Screw Inclined Plane

What is work? ®  In science, work is done

when a force causes an object to move in the direction of the force.

®  Even the person in this picture is doing work by “applying force” to make the ball go the distance.

®  Work = force x distance ®  (W= f x d) Work is measured in

“Joules”

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There is a difference between Force and Work……. ® Applying a force doesn’t always result in

work being done. ®  (Suppose you help push a stalled car. You push and push but

the car doesn’t budge. The “pushing” made you tired, but you haven’t done any work on the car, because the car hasn’t moved.You do “work” on the car, when the car actually moves.) Whenever you apply a force to an object and the object moves in the direction of the force, you have done work on the object.

So when is work done on an object? ®  Work is done on an object

if two things happen: ®  A) the object moves as a

force is applied ®  b) the direction of the

object’s motion is the same as the direction of the force.

®  Is this lady in the picture “holding” the suitcases doing work?

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Machines make work easier… ®  A simple machine is a

device that makes work easier by changing the size or direction of the force.

®  Machines are not just cars, big construction equipment, or computers.

®  You use simple machines everyday such as scissors, chopsticks, etc.

The 6 Types of Simple Machines

Lever Pulley Wheel and Axle

Wedge Screw Inclined Plane

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Machines make work easier… ®  A machine is a device that

makes work easier by changing the size or direction of the force and decreasing the effort needed to move an object.

®  Machines are not just big things like cars, trucks or construction equipment

®  You use simple machines everyday such as computers, scissors, chopsticks, etc.

Inclined Plane ®  The Egyptians used simple machines to build the

pyramids. One method was to build a very long incline out of dirt that rose upward to the top of the pyramid very gently. The blocks of stone were placed on large logs and pushed slowly up the long, gentle inclined plane to the top of the pyramid.

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Inclined Planes ®  An inclined plane is a flat

surface that is sloped (higher on one end) *only simple machine that does not move!

®  Inclined planes make the work of moving things easier by increasing the distance.

®  Trade-off is that object must be moved a longer distance but less force is needed!

®  Ex: ramps, stairways, bath tubs, roof of a house and a door stop etc.

Wedges ® A wedge is a pair of two

inclined planes put together back to back. When these 2 planes meet, they form a sharp edge.

® Wedges are used to split/push things apart and hold things in place. They also increase the distance but decrease effort

® Examples includes an ax, a zipper, farm plows, and the edge of knives.

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Screws:

A screw is a simple machine made up of another simple machine. It is an inclined plane wrapped around a cylinder. This also increases the distance while decreasing the force (effort)

The screw has 2 parts. The inclined plane is the thread that wraps around the screw. The cylinder is the long rod.

Levers: ® A lever is made up of a board or bar that

rests on & pivots around a support. The support that holds up the bar is called a fulcrum. Levers are used to apply force to a load. (--A load is “what you are applying the force on”.)

® Levers are divided into 3 classes according to the way the load and effort are arranged around the fulcrum.

Fulcrumà

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Examples of 1st class levers ® Some common 1st class

levers are see-saws, crowbars, pliers, scissors (which use two first-class levers together), and a hammer pulling a nail.

® 1st class levers change the direction the force

® By moving the fulcrum you can create a different type of lever. Other examples of levers include nut crackers, wheel barrows, doors, and bottle openers.

® 2nd class levers increase the force being applied.

Examples of 2nd class levers:

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3rd class levers change the direction of the force. Examples also include tweezers, arms, hammers, & shovels

3rd Class Levers

®  Fixed pulleys change the direction of the force

®  Movable pulleys increase the force

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Wheel and axle ® A wheel and axle is a

simple machine consisting of a wheel that turns on a center post/rod.

®  This machine increases the distance that that the force is being applied but it in turn decreases the amount of force

WHEEL AND AXEL ®  Fans are also

examples of a wheel and axle. The axel is stuck rigidly to a large wheel. Fan blades are attached to the wheel. When the axle turns, the fan blades spin.

® The blades are also incline planes!

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GEARS are Wheel and Axle ® Each gear in a

series reverses the direction of rotation of the previous gear. The smaller gear will always turn faster than the larger gear.